Focused General Plan Update
Less than significant.
Brea Core Specific Plan
Less than significant.
No mitigation measures are required. Less than significant.
Threshold AE-d: Create a new
source of substantial light or glare
which would adversely affect day
or nighttime views in the area.
Focused General Plan Update
Less than significant.
Brea Core Specific Plan
Less than significant.
No mitigation measures are required. Less than significant.
Section 4.2, Air Quality
Threshold AQ-a: Conflict with or
obstruct implementation of the
applicable air quality plan.
Focused General Plan Update
Potentially significant.
Brea Core Specific Plan
Potentially significant.
MM AQ-1 Site-Specific Air Quality Analysis and Best
Management Practices. Prior to the issuance of a
grading or construction permit for individual
development projects that are not exempt from
California Environmental Quality Act (CEQA), and in
conjunction with any required CEQA review, future
Significant and
unavoidable.
ATTACHMENT H
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project applicants shall submit to the City of Brea
Planning Division documentation that the project is
consistent with the South Coast Air Quality
Management District (South Coast AQMD) mass daily
significance thresholds and localized significance
thresholds (LSTs) for criteria air pollutant emissions
during construction. A project-specific Air Quality
Analysis quantifying the potential air emissions of
project construction shall be prepared by a qualified
air quality professional. This Air Quality Analysis shall demonstrate that criteria air pollutant emissions are
below the South Coast AQMD mass daily significance
thresholds and LSTs. If the Air Quality Analysis
cannot demonstrate that the project is below the
South Coast AQMD thresholds before mitigation, the
project applicant shall implement practices to reduce
VOC and NOX emissions to the extent necessary to
reduce emissions to below South Coast AQMD
thresholds. Best management practices may include,
but are not limited to:
• Use equipment with engines that meet, at a
minimum, the Tier 4 Final California Emissions
Standards, or electric-powered equipment.
• Use architectural coatings that meet “SuperCompliant” VOC standards (as defined in South Coast AQMD Rule 1113) and California Green
Building Standards Code (CalGreen)
requirements under the mandatory measures, or
pre-coated materials such as bathroom stall
dividers, and metal awnings.
• Minimize idling time either by shutting equipment
off when not in use or reducing the time of idling
to 5 minutes. Provide clear signage that posts
this requirement for workers at the entrances to
the site and at construction offices/trailers.
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• Maintain all construction equipment in proper
working condition according to manufacturer’s
specifications. The equipment must be checked
by a certified mechanic and determine to be
running in proper condition before it is operated.
The project applicant shall provide documentation to the City of Brea detailing the measures that would be implemented and that mitigated emissions would be below South Coast AQMD thresholds.
Measures shall be included in project construction documents, and contractors and subcontractors shall implement the applicable South Coast AQMD measures.
Threshold AQ-b: Result in a
cumulatively considerable net
increase of any criteria pollutant for
which the project region is nonattainment under an applicable federal or state ambient air quality
standard).
Focused General Plan Update
Potentially significant.
Brea Core Specific Plan
Potentially significant.
Mitigation Measure MM AQ-1 is required. Significant and unavoidable.
Threshold AQ-c: Expose sensitive
receptors to substantial pollutant
concentrations.
Focused General Plan Update
Potentially significant.
Brea Core Specific Plan
Potentially significant.
No mitigation measures are required. Less than significant.
Threshold AQ-d: Result in other
emissions (such as those leading
to odors) adversely affecting a
substantial number of people.
Focused General Plan Update
Less than significant.
Brea Core Specific Plan
Less than significant.
No mitigation measures are required. Less than significant.
Section 4.3, Biological Resources
Threshold BIO-a: Have a
substantial adverse effect, either
directly or through habitat
modifications, on any species
identified as a candidate, sensitive,
or special status species in local or
Focused General Plan Update
Potentially significant.
Brea Core Specific Plan
Potentially significant.
MM BIO-1 Pre-project/Activity Biological Resources
Survey/Habitat Assessment. For project sites within
vegetation communities and land covers other than
“Urban/Developed,” as shown on Figure 4.3-2,
Vegetation Communities and Land Cover Types, of
this Program Environmental Impact Report for the
Less than significant.
PEIR 4 April 2026
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regional plans, policies, or
regulations, or by the California
Department of Fish and Game or
U.S. Fish and Wildlife Service.
Brea 2050: Focused General Plan Update and Brea
Core Specific Plan, the following requirements shall
apply. Prior to the issuance of any construction or
clearing, grading, or construction permits for
individual development projects that are not exempt
from California Environmental Quality Act (CEQA),
and in conjunction with any required CEQA review,
the future project applicant shall submit one or more
documents to the City of Planning Division for review
and approval, demonstrating that the project site does
not contain native vegetation, sensitive plants, or
undisturbed soils. Examples of acceptable
documentation include, but are not limited to, the
following:
• Aerial photographs (historic and current)
showing grading, building footprints, paving, and
landscaped areas over time to support
ornamental status, existing landscape plans
• Photographic documentation consisting of
georeferenced or dated photographs.
• Landscaping plans or as-built drawings
demonstrating that vegetation was intentionally
planted as part of site development.
• Field survey results prepared by a qualified
biologist confirming that existing plant species
are ornamental and non-native.
Within the future site-specific project areas exhibiting native vegetation, a site-specific biological resources survey shall be conducted during the project design
phase.
The biological resources survey and habitat
assessment shall be conducted by a qualified
biologist and shall include but not be limited to the
following:
PEIR 5 April 2026
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• An analysis of available literature and biological
databases, such as the California Natural
Diversity Database, to determine sensitive
biological resources that have been reported
historically from the proposed project vicinity.
• A review of current land use and land ownership
within the project vicinity.
• An assessment and mapping of vegetation
communities present within the project vicinity. If
vegetation community mapping has not been
conducted on the site in the previous three
years, updated vegetation mapping shall be
conducted by a qualified biologist as part of the
project planning and environmental review
process. Vegetation communities shall be
mapped according to the Manual of California
Vegetation at the alliance level, and a crosswalk
table with Holland vegetation communities shall
be provided.
• A general assessment of the potential for
aquatic resources, including wetlands and
riparian habitats, to occur on site.
• An evaluation of potential local and regional
wildlife movement corridors.
• A focused habitat assessment to determine if the
Project area supports vegetation communities
that may provide habitat for plant or wildlife
species, to be conducted by a qualified biologist,
to determine the potential for sensitive plant or
wildlife species to occur in or adjacent to the
project area.
• If the project area supports sensitive vegetation
communities, the project proponent shall
implement the following weed control methods to
minimize the establishment and spread of non-
PEIR 6 April 2026
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native and invasive weed species in the planning
area during construction activities:
- Seeds and plant materials used for
revegetation shall be certified weed free.
- Straw materials, such as those used for
erosion control, shall be certified weed free.
The results of the biological survey shall be presented in a biological technical report. The survey report shall map and describe the location and extent of observed
sensitive resources, including sensitive vegetation
communities, plant, and wildlife species within the
areas of potential direct and indirect effects for each project area, direct and indirect impacts associated
with construction and operation of a project, and the
need for further survey, monitoring, or mitigation,
including measures pursuant to mitigation measures
MM BIO-2, MM BIO-3, MM BIO-4, MM BIO-5, MM
BIO-6, and MM BIO-7 of this Program Environmental
Impact Report.
MM BIO-2 Focused Sensitive Plant Species Surveys. If
recommended by the Biological Resources
Survey/Habitat Assessment prepared pursuant to
Mitigation Measure MM BIO-1, focused surveys for
future site-specific development shall be conducted,
as applicable, in suitable habitat, to determine
presence/absence of sensitive plant species on the
project site. Focused sensitive plant surveys shall be
conducted during the species’ specific blooming
periods to determine presence/absence. If sensitive
plant species are mapped within any proposed
construction, access, or staging areas, these species
shall be quantified and flagged, and these areas shall
be modified to avoid direct impacts to mapped
sensitive plant species. If significant impacts to these species are unavoidable, the impact on these species
PEIR 7 April 2026
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shall be reduced to a less than significant level
through implementation of one or a combination of
the following actions, in accordance with a
Conceptual Restoration Plan or acquisition of
mitigation credits, reviewed and approved by the City
of Brea:
• Impacted plants shall be salvaged and relocated
to suitable habitat in an on-site restoration area,
if possible. If relocation to a restoration area is
not practical, the plants shall be relocated offsite to an appropriate location determined by a qualified biologist.
• Seeds from impacted plants shall be collected
for use at a local off-site location, as applicable.
• Off-site habitat that supports the species
impacted shall be enhanced or supplemented
with seed collected on site.
• Comparable habitat at an approved off-site
location shall be determined by a qualified
biologist and preserved for relocation,
enhancement, or transplant of the impacted
sensitive plants.
Mitigation that involves relocation, enhancement, or
transplant of sensitive plants shall include all the
following:
• Conceptual planting plan prepared by a qualified
biologist including grading, planting
specifications, and, if appropriate, temporary
irrigation.
• Planting specifications and fencing and signage
to discourage unauthorized access of the
planting site.
• Monitoring program prepared by a qualified
biologist with clearly stated goals and objectives
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and well-defined performance standards that
result in no net loss of sensitive plant resources.
Final success criteria shall be determined based
on quality, quantity, and species of plant
impacted and in consultation with California
Department of Fish and Wildlife and U.S. Fish
and Wildlife Service depending on the status of
the species. The monitoring program will include
measures for adaptive management detailing
remedial actions if success criteria are not met in
the monitoring time frame. Remedial actions
may include, but are not limited to, supplemental
water, replanting, and herbivore
deterrents/protections.
MM BIO-3 Sensitive Vegetation Communities Impacts
Mitigation. If recommended by the Biological
Resources Survey/Habitat Assessment prepared
pursuant to Mitigation Measure MM BIO-1, a
biological survey shall be conducted to ground-truth
and/or update vegetation communities. Any direct
impacts to sensitive vegetation communities require
mitigation to comply with California Department of
Fish and Wildlife authorizations, as well as the ratios defined in any State or Federal permit(s) issued for
the proposed project
Potential direct impacts to sensitive vegetation
communities resulting from project implementation
shall be mitigated prior to any vegetation clearing or
ground-disturbing activities within the site-specific
areas through one of the following three options:
a. Vegetation communities and land cover types will
be verified in the field during the required
biological survey and will be mapped for impact
analysis;
PEIR 9 April 2026
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b. Compensatory mitigation for sensitive habitats
shall be satisfied through the acquisition of
mitigation bank credits via a resource agencyapproved mitigation site within the site’s specific watershed or by acquisition of other off-site
mitigation credits to be identified and selected in
coordination with CDFW. Prior to implementation
of project construction impacts (e.g., vegetation
clearing or ground-disturbing activities) that
would require compensatory mitigation,
documentation demonstrating the availability of
mitigation credits (i.e., credit ledger) at the
approved mitigation site must be submitted to the
City of Brea for confirmation; or
c. If credits are not available at a resource agencyapproved mitigation site within the site’s specific watershed or through other off-site mitigation
credits, implementation of habitat creation,
restoration, enhancement, or preservation shall
occur through a Habitat Mitigation and Monitoring
Plan developed by a qualified biologist. Under
this option, a Habitat Mitigation and Monitoring
Plan shall be provided and prepared to achieve
no net loss of the resource, be timed in relation
to project impacts, and comply with Federal and
State mitigation requirements.
When proposed mitigation involves habitat
enhancement, restoration or creation, the Habitat
Mitigation and Monitoring Plan shall include all of the following information:
• Conceptual planting plan including planting
zones, grading, and irrigation.
• Seed mix/planting palette.
• Planting specifications.
PEIR 10 April 2026
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• Monitoring program prepared by a qualified
biologist including success criteria that ensure
no net loss of sensitive vegetation
communities. Final success criteria shall be
determined based on quality, quantity, and
type of habitat impacted and in consultation
with CDFW. The monitoring program shall
include measures for adaptive management
plan detailing remedial actions if success
criteria are not met in the monitoring time
frame. Remedial actions may include, but are
not limited to, supplemental water, replanting,
and herbivore deterrents/protections.
For mitigation that involves habitat acquisition, the
Habitat Mitigation and Monitoring Plan shall include
all the following:
• Location of proposed acquisition.
• Description of the biological resources to be
acquired, including support for the conclusion
that the acquired habitat mitigates for the
specific maintenance impact.
• Documentation that the mitigation area would
be adequately preserved and maintained in
perpetuity.
The identification of mitigation site credits shall be
provided to the City of Brea and shall include the
following:
• Location of approved mitigation site.
• Description of the mitigation credits to be
acquired, including substantial evidence that
the acquired habitat mitigates for the specific
maintenance impact.
• Documentation of the credits that are
associated with a mitigation bank, which has
PEIR 11 April 2026
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been approved by the appropriate resource
agencies.
• Documentation in the form of a current
mitigation credit ledger.
MM BIO-4 Habitat Restoration for Temporary Impacts. If
recommended by the Biological Resources
Survey/Habitat Assessment prepared pursuant to
Mitigation Measure MM BIO-1, temporary impact
areas shall be restored to pre-construction
topographic contours and conditions, including the
revegetation of native plant communities, where
appropriate, following disturbance and prior to Project completion. Habitat restoration and erosion control
treatments shall be installed within these short-term
impact areas. Habitat revegetation shall feature native species that are typical of the area, and associated
erosion control best management practices shall
include silt fence and microplastic- and weed-free
straw fiber rolls, where appropriate. The revegetation
areas shall be monitored and maintained by a
qualified biologist or restoration specialist for 25
months to ensure adequate establishment and
sustainability of the plantings/seedings.
Where a project activity involves potential disturbance of non-native invasive plant species (as identified by
the California Invasive Plant Council), these plants
shall be entirely removed immediately, where
feasible, and the removal shall be monitored by the
qualified monitoring biologist to ensure that dispersal of propagules (e.g., seeds and stems) are avoided or
minimized. Where removal of plant roots is not
feasible (e.g., where erosive flows are predicted),
aboveground plant material shall be fully removed
and monitored by the qualified monitoring biologist.
Where aboveground plant material cannot be
PEIR 12 April 2026
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removed (e.g., due to limited access), herbicides shall be applied by a licensed pest control advisor, using
chemicals permitted as safe within aquatic
environments.
MM BIO-5 Qualified Monitoring Biologist. If recommended by the Biological Resources Survey/Habitat Assessment
prepared pursuant to Mitigation Measure MM BIO-1,
a qualified monitoring biologist shall be retained to
implement required monitoring. The qualified
monitoring biologist shall be responsible for the
following monitoring and reporting tasks.
a. Biological Construction Mitigation/Monitoring
Exhibit. Prior to the start of construction within
the future site-specific project areas that have
potential to contain sensitive biological resources,
the qualified monitoring biologist shall submit a
Biological Construction Mitigation/Monitoring
Exhibit, which includes limits of work, proposed
monitoring schedule, bird, focused sensitive
species, or other wildlife surveys/survey
schedules (including general bird nesting and
U.S. Fish and Wildlife Service protocol), timing of
surveys, bird construction avoidance areas/noise
buffers/barriers, other impact avoidance areas,
and any subsequent requirements determined by
the qualified monitoring biologist. The Biological
Construction Mitigation/Monitoring Exhibit shall
include the construction site plan, written and
graphic depiction of the proposed project’s
biological mitigation/monitoring program, and a
schedule for construction activities. Where the
potential for impacts to biological resources is
limited (e.g., construction within a footprint that
consists entirely of previously developed or
disturbed lands), the Biological Construction
PEIR 13 April 2026
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Mitigation/Monitoring Exhibit may be limited to a
pre- and post-maintenance verification inspection
by a qualified biologist. For highly sensitive
resource areas with documented sensitive
biological and aquatic resources present, full-time
biological monitors may be required, as
determined by a qualified biologist. The Biological
Construction Mitigation/Monitoring Exhibit shall be
approved by the City of Brea prior to the start of
construction.
b. Resource Marking/Protection. Prior to the start
of construction activities within the future sitespecific project area, the qualified monitoring biologist shall supervise the placement of orange
construction fencing or similar visible marker,
staking, or flagging along the limits of the
construction area adjacent to sensitive biological
habitats, as shown on the Biological Construction
Mitigation/Monitoring Exhibit to ensure crews
remain within the approved construction limits.
These demarcations shall not be required for
areas with existing barriers, such as chain-link
fencing, along the limits or facilities that are within or adjacent to developed and non-sensitive
habitat areas. This task shall include flagging
plant specimens and delineating buffers to protect
sensitive biological resources (e.g., habitats,
sensitive plant and wildlife species, including
nesting birds) prior to construction.
c. Cover Trenches. The qualified monitoring
biologist shall oversee the construction site so
that cover and escape routes for wildlife from
excavated areas shall be provided daily. All
trenches, holes, and excavations during
construction shall be covered at night as directed
PEIR 14 April 2026
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by the monitoring biologist with plywood, metal
plates, or other means, and if plastic sheeting is
used, the edges must be covered with soils such
that small wildlife cannot access the excavated
hole. Soil piles shall be covered at night to
prevent wildlife from burrowing in. The edges of
the sheeting shall be weighed down by sandbags.
These areas may also be fenced to prevent
wildlife from gaining access. Exposed trenches,
holes, and excavations shall be inspected twice
daily (i.e., each morning and before sealing the
exposed area) by the qualified monitoring
biologist to monitor for wildlife entrapment.
Excavations shall provide an earthen ramp to
allow for a wildlife escape route. The qualified
monitoring biologist shall verify that the contractor
has covered all steep-walled trenches or
excavations prior to the end of construction daily.
If wildlife species are encountered within any
trenches or excavated areas, the qualified
monitoring biologist shall remove them, if
possible, or provide them with a means of escape
(e.g., a ramp or sloped surface at no greater than
a 30-degree angle) and allow the species to
disperse. In addition, the qualified monitoring
biologist shall provide training to construction
personnel to increase awareness of the possible
presence of wildlife beneath vehicles and
equipment and to use best judgment to avoid
killing or injuring wildlife (refer to Mitigation
Measure BIO-5e).
d. Structure and Tree Clearance. Prior to the
issuance of any permit to allow for the removal or
demolition of trees and existing structures within
the survey area (particularly any ornamental trees
and existing buildings in the developed land
PEIR 15 April 2026
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areas), the qualified monitoring biologist shall
conduct clearance surveys to flush out any
wildlife species nesting, roosting, or otherwise
occupying the trees or structures. If wildlife
species are encountered within any of the trees or
structures (outside the general bird nesting
season), the qualified monitoring biologist shall
remove them, if possible, or provide them with a
means of escape and allow the species to
disperse. If tree-roosting bats are suspected, slow
removal by gently pushing the tree over with
heavy equipment is required.
e. Pre-Construction Meeting/Education. Prior to
the start of any construction activity where the site
plan for the construction area indicates that
significant impacts to biological resources may
occur, as determined by a qualified biologist, a
pre-construction meeting shall be held on site
with the following in attendance: City of Brea
representatives (project planner and building
inspector), the construction contractor (if
applicable), and the qualified monitoring biologist.
At this meeting, the qualified monitoring biologist
shall identify and discuss the construction
protocols that apply to the proposed activities and
the sensitive nature of the adjacent habitat with
appropriate project personnel.
At the pre-construction meeting, the qualified
monitoring biologist shall submit to the City of
Brea representatives and construction contractor
a copy of the Biological Construction
Mitigation/Monitoring Exhibit that identifies areas
to be protected, fenced, and monitored. This data
shall include all buffer limits, if applicable.
Prior to the start of construction activities, the
qualified monitoring biologist shall meet with the
PEIR 16 April 2026
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construction contractor and crew and conduct an
on-site educational session regarding the need to
avoid impacts outside the approved construction
footprint and to protect sensitive plants and
wildlife that may occur at the specific facility. This
may include but not be limited to explanations of
the bird and wetland buffers, the flag system for
removal of invasive species or retention of
sensitive plants, and clarification of acceptable
access routes/methods and staging areas
f. Biological Monitoring and Reporting. The
qualified monitoring biologist with stop work
authority shall inspect/monitor the project
construction area in accordance with the
approved Biological Construction
Mitigation/Monitoring Exhibit. This may be limited
to pre- and post-maintenance inspections, weekly
visits, or full-time monitoring, as determined by
the qualified monitoring biologist and the City of
Brea.
The qualified monitoring biologist shall document
monitoring events via a Consultant Site Visit
Record. This record shall be sent to the City of
Brea project manager each month. However, if
weekly reports are submitted as part of a
separate agency permit requirement, these
reports may be forwarded to the City of Brea in
place of Consultant Site Visit Record submittals.
If no deviations from the construction site plan
occur during maintenance, no additional
documentation is required. However, if deviations
from the site plan do occur, such as unanticipated
impacts to sensitive vegetation communities or
unanticipated discharge of pollutants, a final
monitoring report shall be prepared within three
months following the completion of mitigation
PEIR 17 April 2026
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monitoring detailing maintenance and monitoring
that occurred, and any remedial or compensatory
measures taken.
MM BIO-6 Focused Sensitive Wildlife Species Surveys. If recommended by the Biological Resources
Survey/Habitat Assessment prepared pursuant to
Mitigation Measure MM BIO-1, focused surveys for
future site-specific development shall be conducted,
as applicable, in suitable habitat, to determine
presence/absence of sensitive wildlife species within
the proposed survey area. If sensitive wildlife species or their habitat are present or potentially present
based on biological surveys, the following measures
shall be implemented.
a. Crotch’s bumble bee. Habitat assessment
surveys for California Endangered Species Act
(CESA) candidate bumble bee species, with a
focus on Crotch’s bumble bee, followed the
California Department of Fish and Wildlife
(CDFW) methodology from the Survey
Considerations for CESA Candidate Bumble Bee
Species dated June 6, 2023 (CDFW Survey
Considerations) (CDFW 2023). If no Crotch’s
bumble bees are found during the focused
surveys, but the habitat assessment identified
suitable nesting, foraging, or overwintering habitat
on the project site, recommendations outlined in
the CDFW Survey Considerations will be
followed, including recommendations that a
biological monitor be on site during vegetation or
ground-disturbing activities that take place during
any of the Queen and Gyne Flight Period and
Colony Active Period. If Crotch’s bumble bees are
observed, project proponents may propose sitespecific measures to avoid take, or consult with PEIR 18 April 2026
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CDFW to obtain an incidental take permit if take
of CESA-protected bumble bees may occur
during project activities.
b. Western spadefoot and Monarch butterfly. If
western spadefoot or monarch butterfly become
listed prior to implementation of future sitespecific development projects, focused surveys and consultation with the U.S. Fish and Wildlife
Service (USFWS) would be necessary.
c. Western burrowing owl. If suitable habitat for
western burrowing owl is present (annual
grassland and agricultural land), a qualified
biologist shall conduct focused surveys of the site
and a 500-foot buffer, as access allows. If no
burrowing owls are identified, no further
measures are necessary. If burrowing owls are
detected, active burrows shall be avoided using
buffers outlined in the Staff Report on Burrowing
Owl Mitigation, dated March 7, 2012, issued by
CDFW. If avoidance is not possible, the qualified
biologist shall consult with CDFW. No direct
disturbance to burrowing owls or their occupied
habitat shall occur without appropriate
authorization from CDFW.
d. Least Bell’s vireo. If suitable habitat for least
Bell’s vireo is present and clearing, grubbing,
grading, or other construction activities may occur
between March 15 and September 15, the
breeding season of the least Bell’s vireo, a
qualified biologist shall conduct focused surveys
for the presence of the least Bell’s vireo of the site
and areas of potentially suitable habitat within 300
feet or that would be subject to construction noise
levels exceeding 60 A-weighted decibels or to the
ambient noise level if it already exceeds 60 A-
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weighted decibel hourly average. If present,
measures to minimize noise impacts (such as
temporary noise walls/berms) may be required.
Noise levels from construction activities during
the avian breeding season should not exceed 60
decibels (dBA Leq; or the ambient noise level if
they already exceed 60 dBA Leq) at the edge of
the occupied habitat. If complete avoidance is not
feasible, the qualified biologist shall consult with
USFWS. No direct harm to the species shall be
allowed without appropriate authorization from
USFWS.
e. Southwestern willow flycatcher. If suitable
habitat for southwestern willow flycatcher is
present and clearing, grubbing, grading, or other
construction activities may occur between April 15
through September 15, the breeding season of
the southwestern willow flycatcher, a qualified
biologist shall conduct focused surveys for the
presence of the southwestern willow flycatcher of
the site and areas of potentially suitable habitat
within 500 feet. If the species is determined to be
present, consultation per Endangered Species
Act with USFWS would be necessary and no
activities would occur until authorized by USFWS.
No direct harm to the species shall be allowed
without appropriate authorization from USFWS.
f. Sensitive Bat Species. If suitable roosting
habitat (e.g., riparian habitat, snags, wooden
buildings, bridges, etc.) for sensitive bat species
is present, a qualified biologist shall conduct
subsequent focused surveys no less than 14 days
prior to removal or disturbance of vegetation or
buildings. The survey shall consist of visual
and/or acoustic methods as deemed appropriate
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by the qualified biologist. If no bats are detected,
no further measures are necessary. If bat species
are detected during surveys, a site-specific plan
shall be developed by the qualified biologist. The
plan may include, as determined by the qualified
biologist, delaying removal of roost habitat until
after the maternity roosting period and exclusion
of bats from roosting habitat prior to removal of
habitat. The qualified biologist shall consult with
CDFW prior to implementing any exclusion
activities.
g. Other Sensitive Species. Prior to any demolition
work, construction or grading activities within the
future site-specific project areas, pre-construction
surveys for other sensitive wildlife species, such
as reptiles, may be required to determine
presence/absence of sensitive wildlife species
within the proposed survey area.
MM BIO-7 Focused Nesting Bird Surveys. Project activities that may directly (e.g., vegetation removal, clearing
and grubbing, building demolition) or indirectly affect (noise, light, or ground vibration) nesting raptors and other protected bird species shall be timed to avoid
the nesting season (January 15 through September
15). If project activities occur within the nesting
season, the qualified monitoring biologist shall
conduct focused surveys for birds in suitable habitat
to determine presence/absence. Surveys shall occur
within seven (7) days prior to any construction or
grading activities within the future site-specific project areas. Focused sensitive bird surveys shall be
conducted during the species’ specific nesting
seasons to determine presence/absence within the
development footprint plus a buffer, if recommended
by the qualified monitoring biologist (refer to
PEIR 21 April 2026
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mitigation measure MM BIO-5). The survey report
shall map and describe the location and extent of
observed sensitive bird species that would be
impacted within the areas of potential effect for each
project area. If no nesting birds are documented
within the individual activity area, construction shall be allowed to proceed. If nesting birds cannot be
completely avoided, a no-disturbance buffer shall be
established around the active nest, the size of which
will be determined by the qualified monitoring
biologist based on species of bird and specific
construction activities to take place. The size of the
buffer can be reduced in consultation with California
Department of Fish and Wildlife. Any work within the
buffer shall be avoided until the nest is inactive, as
determined by the qualified monitoring biologist.
Threshold BIO-b: Have a
substantial adverse effect on any
riparian habitat or other sensitive
natural community identified in
local or regional plans, policies,
regulations or by the California
Department of Fish and Game or
US Fish and Wildlife Service.
Focused General Plan Update
Potentially significant.
Brea Core Specific Plan
Less than significant.
Mitigation Measure MM BIO-1, MM BIO-3, MM BIO-4 and MM BIO-5 are required.
Less than significant.
Threshold BIO-c: Have a
substantial adverse effect on state
or federally protected wetlands
(including, but not limited to,
marsh, vernal pool, coastal, etc.)
through direct removal, filling,
hydrological interruption, or other
means.
Focused General Plan Update
Potentially significant.
Brea Core Specific Plan
Potentially significant.
Mitigation Measure MM BIO-1 is required.
MM BIO-8 Aquatic Resources Delineation. If potentially
jurisdictional aquatic resources are identified during
pre-project/activity surveys pursuant to mitigation
measure MM BIO-1, a qualified biologist shall conduct
a formal aquatic resources delineation following the
methods outlined in the 1987 U.S. Army Corps of
Engineers Wetland Delineation Manual and
applicable Regional Supplement to the U.S. Army
Corps of Engineers Wetland Delineation Manual to
map the extent of wetlands and non-wetland waters,
Less than significant.
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determine jurisdiction, and assess potential impacts.
The results of the delineation shall be presented in an aquatic resources delineation report. The aquatic
resources delineation report shall be used in
consultation with the U.S. Army Corps of Engineers,
Regional Water Quality Control Board, and California
Department of Fish and Wildlife for necessary
authorization or permit, as described in mitigation
measure MM BIO-9.
MM BIO-9 Potentially Jurisdictional Aquatic Resources
Permitting. Temporary and permanent impacts to the
wetland and non-wetland waters potentially under the
jurisdiction of the U.S. Army Corps of Engineers,
Regional Water Quality Control Board, and California
Department of Fish and Wildlife, shall be authorized
by the U.S. Army Corps of Engineers, Regional Water
Quality Control Board, and California Department of
Fish and Wildlife, as applicable. Approved temporary
and permanent impacts to the potentially Federal and
State jurisdictional aquatic resources in the project
area require compensatory mitigation through
proposed on- or off-site habitat restoration, creation, or enhancement to the satisfaction of the U.S. Army
Corps of Engineers, Regional Water Quality Control
Board, and California Department of Fish and Wildlife
to achieve a no-net loss of Federal and State
jurisdictional wetland and non-wetland waters.
Threshold BIO-d: Interfere
substantially with the movement of
any native resident or migratory
fish or wildlife species or with
established native resident or
migratory wildlife corridors, or
impede the use of native wildlife
nursery sites.
Focused General Plan Update
Potentially significant.
Brea Core Specific Plan
Potentially significant.
Mitigation Measure MM BIO-1, MM BIO-3, MM BIO-4, MM BIO-5 and MM BIO-6 are required.
MM BIO-10 Wildlife Corridor Impact Mitigation. The project shall avoid wildlife movement corridors to the maximum
extent feasible, as determined through biological
surveys and review of best available scientific data.
Less than significant.
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If avoidance is determined to be infeasible, the project applicant shall implement measures to minimize
impacts to wildlife movement corridors, subject to
review and approval by the City and applicable wildlife agencies.
Threshold BIO-e: Conflict with any
local policies or ordinances
protecting biological resources,
such as a tree preservation policy
or ordinance.
Focused General Plan Update
Potentially significant.
Brea Core Specific Plan
Potentially significant.
Mitigation Measures MM BIO-1 through MM BIO-9 are required. Less than significant.
Threshold BIO-f: Conflict with the
provisions of an adopted Habitat
Conservation Plan, Natural
Community Conservation Plan, or
other approved local, regional, or
State habitat conservation plan.
Focused General Plan Update
Less than significant.
Brea Core Specific Plan
Less than significant.
No mitigation measures are required. Less than significant.
Section 4.4, Cultural Resources
Threshold CUL-a: Cause a
substantial adverse change in the
significance of a historical resource
pursuant to Section 15064.5.
Focused General Plan Update
Less than significant.
Brea Core Specific Plan
Less than significant.
No mitigation measures are required. Less than significant.
Threshold CUL-b: Cause a
substantial adverse change in the
significance of an archaeological
resource pursuant to Section
15064.5.
Focused General Plan Update
Potentially significant.
Brea Core Specific Plan
Potentially significant.
MM CUL-1 Archaeological Resources Assessment. Prior to
the commencement of projects not exempt under
California Environmental Quality Act (CEQA)
involving ground-disturbing activities (including
grading, excavation, trenching, boring, or demolition
extending below existing grade) in areas that have
not been previously developed or includes unpaved
areas, the project proponent shall provide an
Archaeological Resources Assessment as part of
project-level CEQA review prepared by a qualified
archaeologist., The assessment shall be prepared
under the supervision of an archaeologist meeting the
Less than significant.
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Secretary of the Interior’s professional qualifications standards in prehistoric and/or archaeology.
The assessment shall include:
• A California Historical Resources Information
System records search at the South Central
Coastal Information Center;
• A review of the Native American Heritage
Commission Sacred Lands File; and
• Evaluation of previous cultural resources
investigations and recorded resources within
and adjacent to the project site.
MM CUL-2 Inadvertent Discovery. If archaeological resources are encountered during ground disturbing activities,
work in the immediate area shall cease and an
archaeologist meeting the Secretary of the Interior’s
professional qualifications standards in prehistoric
and/or archaeology shall be contacted immediately to
evaluate the find(s). If the discovery proves to be
significant as determined by the qualified
archeologist, procedures outlined in Mitigation
Measure MM CUL-6 shall be implemented.
MM CUL-3 Evaluation and Mitigation of Significant
Archaeological Resources. If potentially significant
archaeological resources are identified under
Mitigation Measure MM CUL-1 or MM CUL-2, and
avoidance is not feasible, a Phase II Testing and
Evaluation Program shall be conducted to determine
resource significance prior to ground disturbance.
Phase II investigations shall be conducted by a
qualified archaeologist and in coordination with
affiliated California Native American Tribes, where
applicable.
If archaeological resources are determined to be
significant or unique and cannot be avoided,
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appropriate site-specific mitigation shall be
implemented, which may include a Phase III Data
Recovery Program. Data recovery shall be conducted
in accordance with the Office of Historic
Preservation’s guidelines, including Archaeological
Resource Management Reports: Recommended
Contents and Format and Guidelines for
Archaeological Research Designs.
MM CUL-4 Construction Monitoring in High-Sensitivity Areas.
If the Archaeological Resources Assessment identifies
the project site as highly sensitive for archaeological resources, a qualified archaeologist and a Native
American monitor, approved by a California Native
American Tribe identified by the Native American
Heritage Commission as culturally affiliated, shall
monitor all ground-disturbing activities in sensitive
areas.
Prior to construction, the archaeologist shall conduct a worker environmental awareness training addressing
the identification and protection of archaeological
resources. The Native American monitor shall be
invited to participate.
If archaeological materials are discovered, work shall
cease in the vicinity of the discovery until the
resources are evaluated by the qualified
archaeologist, in coordination with the Native
American monitor and affiliated Tribe(s), as
appropriate. The treatment and final disposition of
materials shall be determined through Tribal
consultation and may include curation, repatriation, or reinterment.
MM CUL-5 On-Call Archaeological Monitoring in ModerateSensitivity Areas. If the Archaeological Resources Assessment identifies the project site as having
moderate sensitivity, a qualified archaeologist shall be PEIR 26 April 2026
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retained on an on-call basis. Pre-construction training shall be provided to construction personnel regarding
procedures for unanticipated discoveries.
If archaeological resources are encountered,
construction shall halt in the immediate area, and the
on-call archaeologist shall evaluate the discovery and
initiate Tribal consultation, where applicable.
Appropriate treatment and disposition of materials
shall be determined in consultation with affiliated
Tribe(s).
Threshold CUL-c: Disturb any
human remains, including those
interred outside of dedicated
cemeteries.
Focused General Plan Update
Less than significant.
Brea Core Specific Plan
Less than significant.
No mitigation measures are required. Less than significant.
Section 4.5, Energy
Threshold EN-a: Result in
potentially significant
environmental impact due to
wasteful, inefficient, or
unnecessary consumption of
energy resources, during project
construction or operation.
Focused General Plan Update
Less than significant.
Brea Core Specific Plan
Less than significant.
No mitigation measures are required. Less than significant.
Threshold EN-b: Conflict with or
obstruct a state or local plan for
renewable energy or energy
efficiency.
Focused General Plan Update
Less than significant.
Brea Core Specific Plan
Less than significant.
No mitigation measures are required. Less than significant.
Section 4.6, Geology and Soils
Threshold GEO-f: Directly or
indirectly destroy a unique
paleontological resource or site or
unique geologic feature.
Focused General Plan Update
Potentially significant.
Brea Core Specific Plan
Potentially significant.
MM GEO-1 Prior to issuance of a grading permit for any project that would involve ground-disturbing activities greater than current foundations present on a given site,
underlain by Quaternary (Pleistocene and Holocene)
terrestrial deposits or older geologic units, or within areas identified as having high or undetermined
Less than significant.
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paleontological sensitivity the project proponent shall retain a qualified professional paleontologist meeting
the qualifications of the Society of Vertebrate
Paleontology to conduct an evaluation to determine
the paleontological sensitivity of the geologic units
affected by the project and whether ground-disturbing
activities would result in a significant impact to
paleontological resources according to current
Society of Vertebrate Paleontology guidelines. The
evaluation shall be submitted to the City of Brea
Community Development Department for review and
approval.
If evaluation determines that the project has the
potential to impact paleontological resources, the City of Brea shall require implementation of
paleontological mitigation measures recommended by
the qualified professional paleontologist to reduce
potential impacts to paleontological resources to a
less than significant level. These measures may
include but not be limited to implementation of a
Worker Environmental Awareness Program, on-site
paleontological monitoring, and fossil salvage and
treatment plans, if applicable. If paleontological
resources are discovered during excavation and/or
construction activities, construction shall stop within 25 feet of the find, and the qualified professional
paleontologist shall be consulted to determine
whether the resource requires further study. The
paleontologist shall make recommendations to the
City of Brea to protect the discovered resources. Any
paleontological resources recovered shall be provided
for curation at a local curation facility such as the Dr.
John D. Cooper Archaeological and Paleontological
Center or other appropriate repository. The City of
Brea Community Development Department shall
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review and approve the qualified professional
paleontologist’s findings and recommendation.
Section 4.7, Greenhouse Gas Emissions
Threshold GHG-a: Generate
greenhouse gas emissions, either
directly or indirectly, that may have
a significant impact on the
environment.
Focused General Plan Update
Potentially significant.
Brea Core Specific Plan
Potentially significant (Cumulative
Only)
MM GHG-1 GHG Reduction Plan for Future Development. As
part of the development review process for individual
development projects that are not exempt from CEQA,
the Brea Community Development Department shall
require a greenhouse gas (GHG) emissions technical
analysis prepared by a qualified environmental
professional for all projects exceeding 190 singlefamily dwelling units, 360 multi-family dwelling units, or 56,000 square feet of non-residential square
footage.1 If the GHG technical analysis shows that
construction- or operational-related GHG emissions
project will meet or exceed the South Coast Air
Quality Management District Interim California
Environmental Quality Act GHG Tier 3 Significance
Threshold of 3,000 metric ton carbon dioxide
equivalent (MT CO2e) and per capita threshold of 1.5
MT CO2e per service population, a GHG reduction
plan shall be prepared to reduce GHG emissions to
below the applicable threshold. The GHG reduction
plan shall include potential mitigation measures from
the California Air Pollution Control Officers Association Handbook for Analyzing Greenhouse Gas Emission
Reductions, Assessing Climate Vulnerabilities, and
Advancing Health and Equity. Mitigation measures
shall be selected based on the nature of the project
and characteristics of the GHG emission source(s).
Potential measures include, but are not limited to the
following:
Significant and
unavoidable.
1 Consistent with SCAQMD methodology for the screening levels in Table 3-3 of the Interim CEQA GHG Significance Threshold Draft Guidance Document (SCAQMD 2008), 190 single-family residential units, 360 multi-family residential units, or 56,000 SF of retail development would generate approximately 3,000 MT CO2e annually, assuming default CalEEMod assumptions for Year 2025. See Appendix D for calculation details.
PEIR 29 April 2026
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• Transportation and Land Use: Mobile GHG
emissions can be mitigated through project site
location and design, including:
− Prioritizing infill development with high
destination accessibility
− Improving destination accessibility
− Orient project toward transit, bicycle, or
pedestrian facility
− Locate project near bike path/bike lane
− Provide bike parking, especially near transit
− Provide traffic calming measures to
encourage pedestrian/bicycle activity
− Create urban non-motorized zones
− Construct or improve bicycle and pedestrian
facilities
− Provide first and last mile services to connect
project to existing transit or community
services, such as a shuttle program
− Implement preferential parking permit
program for ride-share participants
− Provide electric vehicle infrastructure beyond
California Green Building Standards Code
(CALGreen) requirements
− Provide end-of-trip bicycle facilities
− Implement a school pool program
− Implement telecommute and/or alternative
work schedule program
− Implement commute trip reduction programs
− Implement paid parking
− Replace traffic controls with roundabout
where appropriate
− Incorporate park-and-ride lots
− Designate zero emissions delivery zones
− Electrify loading docks
− Install hydrogen fueling infrastructure for
projects that include a fleet fueling component
PEIR 30 April 2026
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• Green Building Measures: Building design
beyond CALGreen requirements can reduce
GHG emissions from energy and water use.
Some strategies include:
− Install whole house fans.
− Install energy-saving lighting, heating, cooling
systems, and appliances.
− Design buildings with passive environmental
controls to maximize natural heating and
cooling.
− Install electric vehicle charging stations to
support clean transportation.
− Provide on-site renewable energy generation
systems and storage
− Install electric heat pumps
− Implement yard equipment exchange
program
− Provide electric yard equipment compatibility,
such as outdoor outlets
− Install green or cool roofs
− Provide high efficiency outdoor lighting
− Install cool pavement
− Eliminate the use of natural gas
− Use reclaimed non-potable water for
landscaping
− Use gray water
− Require low-flow fixtures
− Design water efficient landscaping
− Participate in waste diversion programs
• Project Construction: GHG emissions from
construction can be reduced through sustainable
practices such as the following:
− Recycle demolished construction material
beyond CALGreen requirements.
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− Source wood materials from urban wood
reuse program
− Use local and sustainable building materials
− Use local construction contractors
− Use cleaner-fuel equipment
• Natural/Working Lands: Support carbon
sequestration, reduce urban heat island impact,
and improve access to local food sources
through practices such as the following:
− Make public space available for establishment
of a local farmers market
− Establish areas available for community
gardens
− Expand urban tree planting
− Create new vegetated spaces
Threshold GHG-b: Conflict with an
applicable plan, policy or regulation
adopted for the purpose of
reducing the emissions of
greenhouse gases.
Focused General Plan Update
Less than significant.
Brea Core Specific Plan
Less than significant.
No mitigation measures are required. Less than significant.
Section 4.8, Hazards and Hazardous Materials
Threshold HAZ-a: Create a
significant hazard to the public or
the environment through the
routine transport, use, or disposal
of hazardous materials.
Focused General Plan Update
Less than significant.
Brea Core Specific Plan
Less than significant.
No mitigation measures are required. Less than significant.
Threshold HAZ -b: Create a
significant hazard to the public or
the environment through
reasonably foreseeable upset and
accident conditions involving the
release of hazardous materials into
the environment.
Focused General Plan Update
Less than significant.
Brea Core Specific Plan
Less than significant.
No mitigation measures are required. Less than significant.
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Threshold HAZ -c: Emit hazardous
emissions or handle hazardous or
acutely hazardous materials,
substances, or waste within onequarter mile of an existing or proposed school.
Focused General Plan Update
Less than significant.
Brea Core Specific Plan
Less than significant.
No mitigation measures are required. Less than significant.
Threshold HAZ -d: Be located on a
site which is included on a list of
hazardous materials sites compiled
pursuant to Government Code
Section 65962.5 and, as a result,
would it create a significant hazard
to the public or the environment.
Focused General Plan Update
Less than significant.
Brea Core Specific Plan
Less than significant.
No mitigation measures are required. Less than significant.
Threshold HAZ -e: For a project
located within an airport land use
plan or, where such a plan has not
been adopted, within two miles of a
public airport or public use airport,
result in a safety hazard or
excessive noise for people residing
or working in the project area.
Focused General Plan Update
No impact.
Brea Core Specific Plan
No impact.
No mitigation measures are required. No impact.
Threshold HAZ -f: Impair
implementation of or physically
interfere with an adopted
emergency response plan or
emergency evacuation plan.
Focused General Plan Update
Less than significant.
Brea Core Specific Plan
Less than significant.
No mitigation measures are required. Less than significant.
Threshold HAZ -g: Expose people
or structures, either directly or
indirectly, to a significant risk of
loss, injury or death involving
wildland fires.
Focused General Plan Update
Less than significant.
Brea Core Specific Plan
Less than significant.
No mitigation measures are required. Less than significant.
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Section 4.9, Hydrology and Water Quality
Threshold HYD-a: Violate any
water quality standards or waste
discharge requirements or
otherwise substantially degrade
surface or groundwater quality.
Focused General Plan Update
Less than significant.
Brea Core Specific Plan
Less than significant.
No mitigation measures are required. Less than significant.
Threshold HYD-b: Substantially
decrease groundwater supplies or
interfere substantially with
groundwater recharge such that
the project may impede
sustainable groundwater
management of the basin.
Focused General Plan Update
Less than significant.
Brea Core Specific Plan
Less than significant.
No mitigation measures are required. Less than significant.
Threshold HYD-c: Substantially
alter the existing drainage pattern
of the site or area, including
through the alteration of the course
of a stream or river or through the
addition of impervious surfaces, in
a manner which would result in
substantial erosion or siltation onor off-site; substantially increase the rate or amount of surface runoff
in a manner which would result in
flooding on- or offsite; create or
contribute runoff water which would
exceed the capacity of existing or
planned stormwater drainage
systems or provide substantial
additional sources of polluted
runoff; and impede or redirect flood
flow.
Focused General Plan Update
Less than significant.
Brea Core Specific Plan
Less than significant.
No mitigation measures are required. Less than significant.
PEIR 34 April 2026
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Threshold HYD-d: In flood hazard,
tsunami, or seiche zones, risk
release of pollutants due to project
inundation.
Focused General Plan Update
Less than significant.
Brea Core Specific Plan
Less than significant.
No mitigation measures are required. Less than significant.
Threshold HYD-e: Conflict with or
obstruct implementation of a water
quality control plan or sustainable
groundwater management plan.
Focused General Plan Update
Less than significant.
Brea Core Specific Plan
Less than significant.
No mitigation measures are required. Less than significant.
Section 4.10, Land Use and Planning
Threshold LU-a: Physically divide
an established community.
Focused General Plan Update
Less than significant.
Brea Core Specific Plan
Less than significant.
No mitigation measures are required. Less than significant.
Threshold LU-b: Cause a
significant environmental impact
due to a conflict with any land use
plan, policy, or regulation adopted
for the purpose of avoiding or
mitigating an environmental effect.
Focused General Plan Update
Less than significant.
Brea Core Specific Plan
Less than significant.
No mitigation measures are required. Less than significant.
Section 4.11, Noise
Threshold NOI-a: Generation of a
substantial temporary or
permanent increase in ambient
noise levels in the vicinity of the
project in excess of standards
established in the local general
plan or noise ordinance, or
applicable standards of other
agencies.
Focused General Plan Update
Potentially significant.
Brea Core Specific Plan
Potentially significant.
MM NOI-1 Construction Noise Best Practices. Prior to any construction activity, such as grading, site
preparation, or issuance of building permits, a note
shall be provided on the construction plans indicating
that during construction activities, the project
applicant shall be responsible for requiring
contractors to implement the following measures to
limit construction-related noise to a performance
standard of 80 A-weighted decibel equivalent
continuous sound level at the property line of the
nearest sensitive receptor:
Significant and
unavoidable.
PEIR 35 April 2026
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• Brea City Code, Section 8.20.070, limits
construction activity to the daytime hours
between 7:00 a.m. and 7:00 p.m. on Monday
through Saturday. Construction is not allowed
on Sundays and Federal holidays.
• During the entire active construction period,
equipment and trucks used for the project
construction shall use the best available noise
control techniques (e.g., improved mufflers, use
of intake silencers, ducts, engine enclosures,
and acoustically attenuating shields or
shrouds), wherever feasible.
• Require that impact tools (e.g., jack hammers
and hoe rams) be hydraulically or electrically
powered wherever possible. Where the use of
pneumatic tools is unavoidable, an exhaust
muffler on the compressed air exhaust shall be
used along with external noise jackets on the
tools.
• Stationary equipment such as generators and
air compressors shall be located as far as
feasible from nearby noise-sensitive uses.
• Stockpiling shall be located as far as feasible
from nearby noise-sensitive receptors.
• Construction traffic shall be limited—to the
extent feasible—to approved haul routes
established by the City of Brea.
• Signs shall be posted at the job site
entrance(s), within the on-site construction
zones, and along queueing lanes (if any) to
reinforce the prohibition of unnecessary engine
idling. All other equipment shall be turned off if
not in use for more than five minutes.
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• During the entire active construction period and
to the extent feasible, the use of noiseproducing signals, including horns, whistles, alarms, and bells, shall be for safety warning
purposes only. The construction manager shall
use smart back-up alarms, which automatically
adjust the alarm level based on the background
noise level, or switch off back-up alarms and
replace with human spotters in compliance with
all safety requirements and laws.
• Erect temporary noise barriers, where feasible,
when construction noise is predicted to exceed
the noise standards after other measures have
been considered, or occur at nighttime, or when
the anticipated construction duration is greater
than is typical (e.g., two years or more).
MM NOI-2 Roadway Noise Measures. Before the approval of building permits, project applicants for future
development projects proposed as a result of the
Focused General Plan Update shall evaluate whether
projects would have the potential to exceed any of the
following thresholds based on the Brea General Plan
Community Noise and Land Use Compatibility
standards:
• Greater than 1.5 A-weighted decibel increase
for ambient noise environments of 65 Aweighted decibel Community Noise Equivalent Level and higher.
• Greater than 3.0 A-weighted decibel increase
for ambient noise environments of 60 to 64 Aweighted decibel Community Noise Equivalent Level.
• Greater than 5.0 A-weighted decibel increase
for ambient noise environments of less than 60
PEIR 37 April 2026
Brea 2050: Focused General Plan Update and Brea Core Specific Plan Table ES-2. Summary of Environmental Impacts and Mitigation Measures Impact
Level of Significance
Before Mitigation Mitigation Measure
Level of Significance
After Mitigation
A-weighted decibel Community Noise
Equivalent Level.
A project that would potentially exceed the above
thresholds shall complete a site-specific Noise
Technical Study to determine if the project would
result in a significant increase in traffic noise. This Noise Technical Study shall be prepared by a
qualified acoustical analyst. The following screening
levels may be applied to determine whether a Noise
Technical Study is required: 2
• If existing roadway segments serving the
project have an average daily traffic below
1,800, a Noise Technical Study is required if
the project would potentially double segment
average daily traffic
• If existing roadway segments serving the
project have an average daily traffic of 1,800 or
higher, a Noise Technical Study is required if
the project would generate more than 750
average daily trips
If a significant increase in vehicle noise level is
identified as a result of individual project
implementation, the project shall incorporate buffers
or other noise reduction measures to the extent
feasible to reduce noise levels at affected sensitive
receptors to a normally acceptable noise level.
Reduction measures that shall be considered include
but are not limited to alternative road design, reduced speeds, alternative paving, building retrofits to provide additional noise attenuation, and setbacks or buffers
2 Based on the study area segments, a roadway with 1,800 average daily traffic or higher has the potential to exceed 65 A-weighted decibels and be subject to the 1.5 A-weighted decibel increase thresholds. A more than 750 average daily traffic increase has the potential to result in a 1.5 A-weighted decibel Community Noise Equivalent Level increase.
Roadway segment with below 1,800 average daily traffic would generally not generate noise levels above 65 A-weighted decibel Community Noise Equivalent Level and would be subject to the 3 A-weighted decibel Community Noise Equivalent Level or 5 A-weighted decibel Community Noise Equivalent Level thresholds. A doubling of roadway volume typically results in a 3 A-weighted decibel Community Noise Equivalent Level increase in noise level (Caltrans 2013a).
PEIR 38 April 2026
Brea 2050: Focused General Plan Update and Brea Core Specific Plan Table ES-2. Summary of Environmental Impacts and Mitigation Measures Impact
Level of Significance
Before Mitigation Mitigation Measure
Level of Significance
After Mitigation
before berms and walls. The noise reduction
measures shall be designed by a qualified acoustical
engineer. Where noise reduction measures in the
public right-of-way are infeasible, the project applicant shall conduct outreach to potentially affected sensitive receptors to determine the feasibility of noise
reduction measures on private property, including a
noise barrier or building retrofits. Based on affected
receptor response, a qualified acoustical engineer
shall determine the feasibility of a noise barrier on
private property and/or the extent of required building retrofits. The project applicant shall submit plans to
the City of Brea Community Development Department
for review and approval before the start of any
construction. These plans shall demonstrate that the
proposed noise reduction measures would reduce
traffic noise exposure at sensitive receptors to the
extent feasible.
Threshold NOI-b: Generation of
excessive groundborne vibration or
groundborne noise levels.
Focused General Plan Update
Potentially significant.
Brea Core Specific Plan
Potentially significant.
MM NOI-3 Vibration Best Management Practices. Prior to the start of construction activities requiring a Building
Permit that involve typical construction equipment
within 100 feet of the property line of occupied
neighboring uses or within 165 feet of the property
line of occupied neighboring uses with the use of a
vibratory roller (or equivalent), the project applicant shall identify best management practices to be
implemented by the construction contractor to
minimize vibration levels in accordance with the Brea
City Code, Section 20.20.040, limit to ground
vibration. The best management practices shall be
included in project construction documents, including
the Grading Plans and contract with the construction
contractor. Practices may include but not be limited to the following:
Less than significant.
PEIR 39 April 2026
Brea 2050: Focused General Plan Update and Brea Core Specific Plan Table ES-2. Summary of Environmental Impacts and Mitigation Measures Impact
Level of Significance
Before Mitigation Mitigation Measure
Level of Significance
After Mitigation
• Use only properly maintained equipment with
vibratory isolators
• Operate equipment as far from sensitive
receptors as possible
• Use rubber-tired vehicles as opposed to
tracked vehicles
Threshold NOI-c: For a project
located within the vicinity of a
private airstrip or an airport land
use plan or, where such a plan has
not been adopted, within two miles
of a public airport or public use
airport, exposure of people residing
or working in the project area to
excessive noise levels.
Focused General Plan Update
No impact.
Brea Core Specific Plan
No impact.
No mitigation measures are required. No impact.
Section 4.12, Public Services
Threshold PS-a: Result in
substantial adverse physical
impacts associated with the
provision of new or physically
altered governmental facilities,
need for new or physically altered
fire protection facilities, the
construction of which could cause
significant environmental impacts,
in order to maintain acceptable
service ratios, response times or
other performance objectives.
Focused General Plan Update
Less than significant.
Brea Core Specific Plan
Less than significant.
No mitigation measures are required. Less than significant.
Threshold PS-b: Result in
substantial adverse physical
impacts associated with the
provision of new or physically
altered governmental facilities,
need for new or physically altered
Focused General Plan Update
Less than significant.
Brea Core Specific Plan
Less than significant.
No mitigation measures are required. Less than significant.
PEIR 40 April 2026
Brea 2050: Focused General Plan Update and Brea Core Specific Plan Table ES-2. Summary of Environmental Impacts and Mitigation Measures Impact
Level of Significance
Before Mitigation Mitigation Measure
Level of Significance
After Mitigation
police protection facilities, the
construction of which could cause
significant environmental impacts,
in order to maintain acceptable
service ratios, response times or
other performance objectives.
Threshold PS-c: Result in
substantial adverse physical
impacts associated with the
provision of new or physically
altered governmental facilities,
need for new or physically altered
schools, the construction of which
could cause significant
environmental impacts, in order to
maintain acceptable service ratios,
response times or other
performance objectives.
Focused General Plan Update
Less than significant.
Brea Core Specific Plan
Less than significant.
No mitigation measures are required. Less than significant.
Threshold PS-d: Result in
substantial adverse physical
impacts associated with the
provision of new or physically
altered governmental facilities,
need for new or physically altered
parks, the construction of which
could cause significant
environmental impacts, in order to
maintain acceptable service ratios,
response times or other
performance objectives.
Focused General Plan Update
Less than significant.
Brea Core Specific Plan
Less than significant.
No mitigation measures are required. Less than significant.
Threshold PS-e: Result in
substantial adverse physical
impacts associated with the
provision of new or physically
altered governmental facilities,
Focused General Plan Update
Less than significant.
Brea Core Specific Plan
Less than significant.
No mitigation measures are required. Less than significant.
PEIR 41 April 2026
Brea 2050: Focused General Plan Update and Brea Core Specific Plan Table ES-2. Summary of Environmental Impacts and Mitigation Measures Impact
Level of Significance
Before Mitigation Mitigation Measure
Level of Significance
After Mitigation
need for new or physically altered
other public facilities, the
construction of which could cause
significant environmental impacts,
in order to maintain acceptable
service ratios, response times or
other performance objectives.
Section 4.13, Transportation
Threshold TRA-a: Conflict with a
program, plan, ordinance or policy
addressing the circulation system,
including transit, roadway, bicycle
and pedestrian facilities.
Focused General Plan Update
Less than significant.
Brea Core Specific Plan
Less than significant.
No mitigation measures are required. Less than significant.
Threshold TRA-b: Conflict or be
inconsistent with CEQA Guidelines
section 15064.3, subdivision (b).
Focused General Plan Update
Less than significant.
Brea Core Specific Plan
Less than significant.
No mitigation measures are required. Less than significant.
Threshold TRA-c: Substantially
increase hazards due to a
geometric design feature (e.g.,
sharp curves or dangerous
intersections) or incompatible uses
(e.g., farm equipment).
Focused General Plan Update
Less than significant.
Brea Core Specific Plan
Less than significant.
No mitigation measures are required. Less than significant.
Threshold TRA-d: Result in
inadequate emergency access.
Focused General Plan Update
Less than significant.
Brea Core Specific Plan
Less than significant.
No mitigation measures are required. Less than significant.
Section 4.14, Tribal Cultural Resources
Threshold TCR-a: Cause a
substantial adverse change in the
significance of a tribal cultural
resource, defined in Public
Resources Code section 21074 as
Focused General Plan Update
Potentially significant.
Brea Core Specific Plan
Potentially significant.
MM TCR-1 Provision of Tribal Monitor. Prior to commencement of any ground-disturbing activities for qualifying
development projects in which the potential exists for
Tribal Cultural Resources to be present based on
record searches or tribal knowledge, the project
Less than significant.
PEIR 42 April 2026
Brea 2050: Focused General Plan Update and Brea Core Specific Plan Table ES-2. Summary of Environmental Impacts and Mitigation Measures Impact
Level of Significance
Before Mitigation Mitigation Measure
Level of Significance
After Mitigation
either a site, feature, place, cultural
landscape that is geographically
defined in terms of the size and
scope of the landscape, sacred
place, or object with cultural value
to a California Native American
tribe, and that is: 1) listed or
eligible for listing in the California
Register of Historical Resources,
or in a local register of historical
resources as defined in Public
Resources Code section 5020.1(k);
or 2) a resource determined by the
lead agency, in its discretion and
supported by substantial evidence,
to be significant pursuant to criteria
set forth in subdivision (c) of Public
Resources Code Section 5024.1.
In applying the criteria set forth in
subdivision (c) of Public Resource
Code Section 5024.1, the lead
agency shall consider the
significance of the resource to a
California Native American tribe.
applicant shall coordinate with all interested Staterecognized Tribes in concurrence with the City of Brea as the California Environmental Quality Act
(CEQA) lead agency. A copy of the executed contract
shall be submitted to the City of Brea Community
Development Department prior to the issuance of any
permit necessary to commence a ground-disturbing
activity.
• The Tribal monitor will only be present on-site
during the construction phases that involve
ground-disturbing activities. Ground-disturbing
activities are defined by the Consulting Tribe as
activities that may include, but are not limited
to, pavement removal, potholing or augering,
grubbing, tree removals, boring, grading,
excavation, drilling, and trenching. The Tribal
monitor shall complete daily monitoring logs
describing construction activities, locations, soil
conditions, and any cultural materials identified.
The monitoring shall end when all grounddisturbing activities are completed, or when the qualified archaeologist and/or Tribal monitor
determines that all remaining ground-disturbing
activities have little to no potential for impacting
Tribal Cultural Resources.
• Upon discovery of any Tribal Cultural
Resources, construction activities shall cease
in the immediate vicinity of the find (not less
than the surrounding 100 feet) until the find can
be assessed. All Tribal Cultural Resources
unearthed by project activities shall be
evaluated by the qualified archaeologist and
Tribal monitor. If the resources are Native
American in origin, the Consulting Tribe will
retain Tribal Cultural Resources in the form
and/or manner the Consulting Tribe deems
PEIR 43 April 2026
Brea 2050: Focused General Plan Update and Brea Core Specific Plan Table ES-2. Summary of Environmental Impacts and Mitigation Measures Impact
Level of Significance
Before Mitigation Mitigation Measure
Level of Significance
After Mitigation
appropriate, for educational, cultural and/or
historic purposes.
• If human remains and/or grave goods are
discovered or recognized at the projects site, all
ground disturbance shall immediately cease
within 100 feet of discovery, and the county
coroner shall be notified per Public Resources
(PRC), Code Section 5097.98, and Health and
Safety Code, Section 7050.5. Human remains
and grave/burial goods shall be treated alike
per PRC Section 5097.98(d)(1) and (2).
• Work may continue on other parts of the project
site while evaluation and, if necessary,
mitigation takes place (CEQA Guidelines,
Section 15064.5(f)).
• If a non-Native American resource is
determined by the qualified archaeologist to
constitute as a “historical resource” or “unique
archaeological resource,” time allotment and
funding sufficient to allow for implementation of
avoidance measures, or appropriate mitigation,
must be available. The treatment plan
established for the resources shall be in
accordance with CEQA Guidelines Section
15064.5(f) for historical resources and PRC
Section 21074(b) for unique archaeological
resources.
MM TCR-2 Discovery of Cultural Resources (Not Native
American in Origin): Prior to commencement of any
ground-disturbing activity at the project site, the
project applicant shall retain an archaeologist meeting the Secretary of the Interior’s Professional
Qualifications Standards for Archaeology (National
Park Service [NPS] 1983). If cultural resources that
are not Native American in origin are encountered
PEIR 44 April 2026
Brea 2050: Focused General Plan Update and Brea Core Specific Plan Table ES-2. Summary of Environmental Impacts and Mitigation Measures Impact
Level of Significance
Before Mitigation Mitigation Measure
Level of Significance
After Mitigation
during ground-disturbing activities, construction
activities shall cease in the immediate vicinity of the find (not less than the surrounding 100 feet) until the find can be assessed. If the discovery proves to be
significant as determined by the site archaeologist,
additional work such as data recovery excavation
may be warranted and shall be reported to the City of
Brea Community Development Department.
Section 4.15, Utilities and Service Systems
Threshold UTL-a: Require or result
in the relocation or construction of
new or expanded water,
wastewater treatment or storm
water drainage, electric power,
natural gas, or telecommunications
facilities, the construction or
relocation of which could cause
significant environmental effects.
Focused General Plan Update
Potentially significant.
Brea Core Specific Plan
Potentially significant.
MM UTL-1 Water and Sewer Infrastructure Improvements.
Prior to approval of any discretionary development
permit or issuance of building permits, the project
applicant shall demonstrate compliance with the City
of Brea’s Water Master Plan, and Sewer Master Plan,
as well as all applicable improvement and design
requirements of the City of Brea Public Works
Department and the City’s Capital Improvement
Program (CIP).
As part of the development application review
process, the applicant shall retain a qualified licensed civil engineer to evaluate existing water and sewer
system conditions serving the project site. If the
evaluation identifies any capacity deficiencies or
facility constraints, the applicant shall prepare and
submit the appropriate system testing and modeling
(e.g., water flow testing, water hydraulic modeling,
sewer capacity modeling and capacity analysis) to the
Public Works Department for review and approval.
The modeling shall identify the specific infrastructure upgrades, improvements, and associated costs
required to ensure adequate service capacity and
compliance with City design standards.
The applicant shall construct, or fund the construction of, all improvements identified through the approved
modeling and required by the Public Works
Less than significant.
PEIR 45 April 2026
Brea 2050: Focused General Plan Update and Brea Core Specific Plan Table ES-2. Summary of Environmental Impacts and Mitigation Measures Impact
Level of Significance
Before Mitigation Mitigation Measure
Level of Significance
After Mitigation
Department prior to occupancy or in accordance with
a timing and phasing plan approved by the City. No
development shall be permitted to proceed unless all
required improvements or fair-share contributions are
secured through conditions of approval, improvement
plans, or a development agreement.
Threshold UTL-b: Have sufficient
water supplies available to serve
the project and reasonably
foreseeable future development
during normal, dry and multiple dry
years.
Focused General Plan Update
Less than significant.
Brea Core Specific Plan
Less than significant.
No mitigation measures are required. Less than significant.
Threshold UTL-c: Result in a
determination by the wastewater
treatment provider which serves or
may serve the project that it has
adequate capacity to serve the
project’s projected demand in
addition to the provider’s existing
commitments.
Focused General Plan Update
Less than significant.
Brea Core Specific Plan
Less than significant.
No mitigation measures are required. Less than significant.
Threshold UTL-d: Generate solid
waste in excess of State or local
standards, or in excess of the
capacity of local infrastructure, or
otherwise impair the attainment of
solid waste reduction goals.
Focused General Plan Update
Less than significant.
Brea Core Specific Plan
Less than significant.
No mitigation measures are required. Less than significant.
Threshold UTL-e: Comply with
federal, state, and local
management and reduction
statutes and regulations related to
solid waste.
Focused General Plan Update
Less than significant.
Brea Core Specific Plan
Less than significant.
No mitigation measures are required. Less than significant.
PEIR 46 April 2026
Brea 2050: Focused General Plan Update and Brea Core Specific Plan Table ES-2. Summary of Environmental Impacts and Mitigation Measures Impact
Level of Significance
Before Mitigation Mitigation Measure
Level of Significance
After Mitigation
Section 4.16, Wildfire
Threshold 1: Substantially impair
an adopted emergency response
plan or emergency evacuation
plan.
Focused General Plan Update
Less than significant.
Brea Core Specific Plan
Less than significant.
No mitigation measures are required. Less than significant.
Threshold 2: Due to slope,
prevailing winds, and other factors,
exacerbate wildfire risks, and
thereby expose project occupants
to, pollutant concentrations from a
wildfire or the uncontrolled spread
of a wildfire.
Focused General Plan Update
Less than significant.
Brea Core Specific Plan
Less than significant.
No mitigation measures are required. Less than significant.
Threshold 3: Require the
installation or maintenance of
associated infrastructure (such as
roads, fuel breaks, emergency
water sources, power lines or other
utilities) that may exacerbate fire
risk or that may result in temporary
or ongoing impacts to the
environment.
Focused General Plan Update
Less than significant.
Brea Core Specific Plan
Less than significant.
No mitigation measures are required. Less than significant.
Threshold 4: Expose people or
structures to significant risks,
including downslope or
downstream flooding or landslides,
as a result of runoff, post-fire slope
instability, or drainage changes.
Focused General Plan Update
Less than significant.
Brea Core Specific Plan
Less than significant.
No mitigation measures are required. Less than significant.
GENERAL PLAN AMEND. NO. 2026-01, SP, ZOTA EIR - Page 2 of 2
ATTACHMENT I
Bev Perry
City of Brea
Community Development Department
Planning Division
Email: [email protected]
Re: Comments on the Focused General Plan Update (GPU) and the related Program Environmental Impact Report (PEIR)
Dear City of Brea Planning Staff:
First of all, I ask that the Shute, Mihaly & Weinberger letter of 9/24/25 on behalf of Hills For Everyone for the GPU be included as part of the Areas of Controversy in the PEIR. They were not originally included and they should be, along with the comments in a new letter sent by Shute, Mihaly & Weinberger on 3/30/26.
Besides agreeing with the points raised in the letters listed above, I have to admit that I'm very concerned that while the General Plan states that development in the City's hillside areas are subject to hillside development policies and the City’s goals are to preserve ridge lines, riparian areas, creeks, streams, wetlands, and wildlife habitat; avoid oil production hazards (ongoing and residual); avoid earthquake fault zones; and minimize fire hazards, the GPU allows for 1663 units in the 3325 acres with the Hillside Development designation.
As the Hills For Everyone letter points out, why not explicitly point out that the City would, through a Transfer of Development Rights program, allow owners to convert hillside density rights into a tradable asset that could be provided to infill developers who want more density in the City's core areas? A 30% increase in houses and residents is unsustainable, especially in our hills!
Finally, the GPU doesn't appear to comply with AB 1889 which requires adoption of a wildlife connectivity element (WCE). Brea should develop, as Hills For Everyone has asked several times, a stand-alone WCE for the General Plan. As a city with hillsides on two sides, we should be at the forefront of managing our plant and wildlife movements through the hills.
Sincerely,
Bev Perry
ATTACHMENT J
550 CALIFORNIA STREET, SUITE 1200
SAN FRANCISCO, CA 94104
T: (415) 552-7272 F: (415) 552-5816
www.smwlaw.com
EDWARD T. SCHEXNAYDER
Attorney
[email protected]
March 30, 2026
Via Electronic Mail Only
City of Brea
Community Development Department
Planning Division
Email: [email protected]
Re: Comments on the Focused General Plan Update (GPU) and the related Program Environmental Impact Report (PEIR)
Dear City of Brea Planning Staff:
On behalf of Hills For Everyone, we are submitting these comments on the Draft PEIR for the City’s Focused General Plan Update (GPU) and Brea Core Specific Plan (BCSP) as well as the General Plan Update itself. Hills For Everyone is a non-profit organization that works to protect, preserve, and restore the environmental resources and natural environs of the Puente-Chino Hills and surrounding areas for the enjoyment of current and future generations. The organization has been working in the region since 1978, and, along with the City of Brea, was instrumental in the creation and expansion of Chino Hills State Park.
This firm submitted a letter dated September 24, 2025 on the Notice of Preparation for the Draft PEIR, which provided comments on behalf of Hills For Everyone regarding policy direction that should be included in the GPU as well as suggestions on issues that should be evaluated in the PEIR. However, our letter was not included in Appendix B to the PEIR (NOP Comments) nor was it summarized in PEIR Table 1-1 (NOP Comments Summary), despite us having received confirmation that it was received (See Exhibit A).
The concerns raised in the letter, along with issues that the GPU and PEIR should address, were not included in the “Areas of Controversy” enumerated on p. ES-56 of the PEIR.
We submit these comments to again express Hills for Everyone’s concerns regarding the GPUs potentially significant impacts on the area’s natural resources and the City of Brea
March 30, 2026
environment, and to again reiterate policy suggestions for inclusion in the GPU that can reduce potential environmental impacts.
I. Introduction and Background
As proposed, the Brea GPU and BCSP (“Project”) would allow significant amounts of new development in Brea:
Residential
Units
Population Non-Residential Square
Footage (NRSF)
Jobs
Existing Conditions (2025) 16,345 46,585 21,480,414 51,937 Proposed GPU and BCSP
(2050 horizon)
23,736 67,647 30,587,193 73,709
Increase
(Subject of EIR analysis)
7,391 units
(31% increase)
21,062 persons
(31% increase)
9,106,779 square feet
(30% increase)
21,772 jobs
(30% increase)
This table demonstrates notable changes in the amount of:
• Potential for additional Residential Units and Population in the Hillside Residential, MU-50, Brea 265 Specific Plan, and Proposed Brea Core Study Area GP land use designations; and
• Potential for additional Non-Residential Square Footage and Jobs in the General Commercial, General Industrial, Light Industrial, MU-18, MU-50, Public Facilities, Recreational Commercial, Brea 265 Specific Plan, Brea Industrial Specific Plan, and Proposed Brea Core Study Area GP land use designations.
Increases of roughly 30% in each of the categories above table show the substantial change in the number of people, buildings, and jobs for the City. When examining the environmental impacts of this growth at the programmatic level, the City must disclose all it reasonably can now. The PEIR acknowledges the “EIR can serve to streamline environmental review of future projects.” PEIR at 1-1. In fact, under recentlyadopted State legislation including Assembly Bill 130 (2024), many projects that conform with the General Plan land use designations and associated zoning will be exempt from further CEQA review. Thus, the GPU PEIR analysis may be the first, and last, consideration of environmental impacts from those exempt categories of projects.
For this reason, it is imperative that the PEIR thoroughly and properly analyze and, if necessary, mitigate for, the potential environmental impacts of the development allowed City of Brea
March 30, 2026
under the GPU and BCSP. See Cleveland National Forest Foundation v. San Diego Assn. of Governments (2017) 17 Cal.App.5th 413, 441 (program EIRs must provide sufficient detail to decisionmakers so that they can evaluate a project’s environmental impacts). For this reason, the GPU should include policies and implementation actions that can serve to reduce the environmental impacts of future development through measures that be taken either proactively or in coordination with future projects. CEQA Guidelines § 15126.4(a)(2).
II. General Plan Policy Considerations
The City of Brea has long supported smart development within the City while valuing the recreation, open space, and wildlife habitat conservation areas that lie both within and beyond the City limits. This GPU is the perfect time to acknowledge the City’s past efforts in this area and ensure that the next 20 years are guided by the City’s Community Vision Plan published in 2024, which anticipates that “[b]alanced growth and inclusivity are valued. The natural environment, including open spaces, hillsides and wildlife, is well-preserved. The City also provides essential infrastructure and amenities to meet the needs of current and future community members. Diverse representation in decision-making fosters community cohesion. The City preserves what makes it special, while adapting to a changing world and cultivating a prosperous future for all people who live, work, and visit Brea.” See Community Vision Plan at 1.
Two key Guiding Principles from the Vision Plan are Guiding Principle 5:
Resilience for Future Generations and Guiding Principle 6: Connection to Nature.
Guiding Principle 5 explains how Brea sees itself as a forward-thinking city ready to take on the challenges of a changing climate. This principle states that “[p]roactive measures to combat extreme weather, including shade tree planting, water management practices, and wildfire preparedness, enhance both environmental sustainability and quality of life.
Through these comprehensive efforts, Brea is a resilient, livable community for current and future generations.” See Community Vision Plan at 6. Guiding Principle 6 supports Brea’s commitment to providing recreation and open spaces for human and non-humans alike. This principle recognizes that “[T]he surrounding hills and open spaces further enrich Brea’s outdoor offerings, providing opportunities for sports, leisure, and a deeper connection to nature.” See Community Vision Plan at 7.
This GPU is Brea’s opportunity to adopt policies that align with these Guiding Principles and the City’s long-standing conservation values of protecting the hills. The City has repeatedly demonstrated these values through the its support of the Wildlife Corridor Conservation Authority (WCCA), establishment of Chino Hills State Park, and formation of the Hillside Open Space Education Coalition (HOSEC). Brea’s efforts, in combination with those of other local and regional agencies, have resulted in the City of Brea
March 30, 2026
preservation of significant areas of land in the Puente-Chino Hills corridor. In this GPU, Brea can implement policies and programs that will further the community vision as well as bolster the substantial public investments already made in open space and habitat preservation.
In our NOP comment letter, Hills For Everyone encouraged Brea to adopt GPU policies in four key categories: 1) Discouraging development in hillside areas within the Brea’s Sphere of Influence; 2) Emphasizing both fire safety and wildlife protection at the urban edge that is based on sound science and does not remove more protective habitat cover than is necessary; 3) Bringing the General Plan into compliance with new State laws that prioritize wildlife corridors and habitat connectivity; and 4) Supporting urban greening and climate resiliency. The GPU has established some laudable goals and policies, but its implementing actions fall short of identifying how the aspirational policy statements will become reality. We have identified proposed additional actions or revisions to proposed actions for several General Plan Elements that can better implement the categories listed above. All new language proposed is shown in underline.
A. Policy Direction in the Community Development (CD) Element and Urban Design Framework (Appendix A).
The Community Development Element contains goals, policies, and actions related to hillside development, infrastructure, and growth management, among others.
Hills for Everyone’s primary concern is protecting the area’s diverse hillside areas from development so they may continue to provide habitat and connectivity for the natural flora and fauna in the area. The General Plan recognizes this as an important goal and further notes that “[P]roperties designated Hillside Residential are moderately to severely constrained by unique or significant features such as ridgelines, earthquake faults, steep and/or unstable slopes, creeks, sensitive habitat, sensitive wildlife species, mapped landslides, soil conditions, accessibility issues, and wildland fire hazards. Such properties are subject to the City’s Hillside Zoning Ordinance.” GPU at 40. The GPU further acknowledges that development in these constrained areas is subject to hillside development policies and the City’s goals to preserve ridgelines, riparian areas, creeks, streams, wetlands, and wildlife habitat; avoid oil production hazards (ongoing and residual); avoid earthquake fault zones; minimize fire hazards; require adequate levels of public services; and meet project-related and cumulative infrastructure demands. Id. at
46. Although the Hillside Residential areas are physically constrained, the GPU still allows for the development of 1,663 units in the 3,325 acres with this land use designation. GPU Table CD-2 at 45. The GPU relies entirely on regulating development once it arrives, but the GPU should also contemplate making preservation an City of Brea
March 30, 2026
economically rational choice for property owners. A Transfer of Development Rights (TDR) program would allow owners to convert hillside density rights into a tradeable asset that could be provided to infill developers who want more density in the City’s core areas. A proposed new action is included in the section below.
Existing CD Goals
CD-2: Create a visually appealing and cohesive community that emphasizes high-quality design, celebrates Brea’s distinct character, and fosters a strong sense of place through well-designed spaces, architecture, and streetscapes.
CD-4: Minimize the extent of development in the hillsides and mitigate any adverse consequences associated with urbanization.
CD-6: Promote balanced growth with supporting public services infrastructure.
Existing CD Policies
CD-2.3: Streetscape Design. Provide public space streetscapes that balance aesthetics and functionality, with a focus on the City’s arterial highways, entry gateways, and the Core Area. This includes cohesive design elements such as street furniture, lighting, drought-tolerant landscaping in medians and parkways, and monument signage that enhance Brea’s image and provide a welcoming, visually elevated experience for both residents and visitors.
CD-4.2: Constraints. Base allowable development on the ability of infrastructure, landform, physical constraints, and emergency response capabilities to support new development.
CD-4.3: Natural Grading. Encourage natural grading techniques that blend with existing topography; grading should use rounded contours on slopes to minimize disturbance. Encourage the preservation of the physical shape of the hillsides and views where feasible.
CD-4.4: Hillside Zoning Ordinance. Enforce the City’s Hillside Zoning Ordinance, which establishes standards for permitted density on slopes, subdivision design, ridgeline preservation, grading, retaining walls, and other requirements.
CD-4.5: Regional Coordination. Coordinate with Orange County and emphasize the City’s need to participate in the development review process of projects proposed in surrounding unincorporated areas. Work to ensure that such developments proceed consistent with City standards.
CD-4.6: Natural Fire Breaks. Preserve natural fire breaks through designated Open Space land use.
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CD-6.5: Growth Pattern. Strongly encourage new development in infill locations in a balanced and efficient pattern that reduces sprawl, preserves open space, and creates convenient connections to other land uses and transportation facilities.
Existing CD Actions
CD-4a: Require a constraints analysis for properties zoned Hillside Residential. The constraints analysis shall include a detailed description and mapping of slopes, geologic factors, areas prone to flooding and any sensitive biological resources.
CD-4b : Require continued implementation of the City’s Hillside Zoning Ordinance.
In addition to the goals, policies, and actions in the Community Development Element, the Urban Design Framework (General Plan Appendix A) contains a section of urban design guidelines that pertain specifically to the Hillside Residential “development type.” The General Plan specifically notes that these are recommendations:
• Preserve riparian areas, creeks, streams, wetlands, and wildlife habitat; preserve natural slopes; avoid oil production hazards (ongoing and residual); avoid earthquake fault zones; and minimize fire hazards.
• Revegetate with native and/or naturalized species where grading or other activities have disturbed the site.
• Tree selections and plantings shall utilize non-invasive species and those not prone to high flammability. In general, planting should be drought resistant and control erosion.
• Design unobtrusive dwellings, requiring stepped, single story, and low profile building and roof forms that conform to the hillside topography. Tall building forms that block views and detract from the largely undeveloped character of the hillsides are strongly discouraged.
• Incorporate architectural features that reduce bulk, such as eaves, bay windows, and varied elevations. Naturalistic materials and colors are encouraged. • Restrict construction on environmentally sensitive and visually prominent locations. Dwellings should be sited well below the ridgeline and avoid prominent landforms, site features, drainageways, and vegetation. • Use naturalistic grading techniques that blend grading with the existing topography. Grading should use rounded contours and slopes to minimize the apparent disturbance to the site.
While following these recommendations will help minimize the visual and physical impact of Hillside Residential development, most of the recommendations are City of Brea
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subjective and unenforceable in the context of State Housing law. Developing standards that are written clearly and objectively so that they can be relied upon for determining project consistency (or need for design changes to ensure consistency) is important to make these recommendations effective so that they can guide any future development in the Hillsides.
Proposed Additional Actions:
Establish objective design criteria for development in the Hillside Residential General Plan land use designation and the Hillside Residential Zoning District. The objective criteria should be derived from the recommendations in the Hillside Residential section of the Urban Design Framework.
Define thresholds for permitting development on parcels in Brea’s Sphere of Influence (SOI) that are designated Hillside Residential. Thresholds should include allowing development only when accompanied by a Fire Protection Plan and fuel modification plans, establishing minimum evacuation standards and multiple ingress/egress route requirements, and minimizing impacts to biological resources.
Establish a mapped Conservation Priority Overlay for hillside SOI parcels that meet defined ecological, geologic, or scenic threshold criteria (e.g., average slope >25%, presence of sensitive habitat, location within a mapped wildlife corridor, etc.). Within this overlay, the City shall: (a) make open space preservation the preferred outcome of any annexation discussion; and (b) require an Open Space Deed Restriction or Conservation Easement as a condition of any annexation.
Establish a Transfer of Development Rights (TDR) program that allows development potential to be transferred from high-value conservation lands in the hillsides to appropriate infill receiving zones in the city core (such as the Brea Core Specific Plan Area).
B. Policy Direction in the Community Resources (CR) Element.
The Community Resources Element acknowledges that “woodlands, grasslands, and chaparral areas provide important open space, natural resources, and scenic vistas, but also create fire hazards when development is located in or adjacent to these areas,” explicitly recognizing the tension between fire safety and habitat protection. The Brea Fire Department has set a minimum distance of 170 feet beyond the construction boundary of any property on which a new structure can be built as its fuel modification zone within the designated High Fire Hazard and Very High Fire Hazard Severity Zones.
However, one of concerns is that the 170-foot fuel modification standard is applied as a blanket rule without biological review. Current science (including work from UC City of Brea
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Cooperative Extension and CAL FIRE) supports a risk-based, site-specific approach to fuel modification that can achieve equivalent fire safety with substantially smaller disturbance in certain habitat types. As currently written, there is no distinction between habitat types in the fuel modification zones. The fuel modification requirements should have different standards for thinning in chaparral (which has evolved with fire) than clearing coastal sage scrub (which hosts California gnatcatcher and other listed species) and should be retained to the greatest degree possible. There is also no science-based fireresistant landscaping palette that is required. Fuel Modification Zone B (50 feet, replanting/irrigated) could be replanted with native, fire-resistant species that provide some habitat value, but the fuel modification standards do not require this. The June 2014 Brea fire example in the Safety Element (GPU at 170) demonstrates this is effective, but it is not codified as a standard. These items are suggested new actions to be included in the GPU.
As drafted, the GPU does not appear to comply with Assembly Bill (AB) 1889, which requires adoption of a wildlife connectivity element, or to ensure that wildlife connectivity goals, policies, and actions are included in other elements. To comply with AB 1889, the GPU must, among other things, identify and analyze connectivity areas, permeability, and natural landscape areas, identify and analyze existing or planned wildlife passage features, and consider the impacts of development and the barriers caused by development to wildlife, as defined, and habitat connectivity. Developing a stand-alone Wildlife Connectivity Element for the General Plan would be the most comprehensive approach. Government Code section 65302(d) also requires the City to incorporate information from a state plan on wildlife connectivity and best available science. To ensure compliance with the requirements of AB 1889, the GPU should incorporate recommendations from scientific sources, such as “Maintaining Ecological Connectivity Across the Missing Middle of the Puente-Chino Hills Corridor,” by Dr.
Wayne Spencer at the Conservation Biology Institute. Dr. Spencer’s report builds on several previous ecological and wildlife movement studies in the Puente-Chino Hills, as well as the general literature on wildlife movement corridors where it applies to this valuable corridor. The report is included as Exhibit B to this letter.
AB 1889 also establishes a statewide framework for wildlife crossings and requires state agencies to prioritize them. SR-57 is a significant wildlife movement barrier between the Chino Hills and Puente Hills systems. Putting language in the GPU related to the need to address this barrier will better position Brea to access Caltrans and/or federal wildlife crossing funds. (The Federal Infrastructure Investment and Jobs Act included $350M for wildlife crossings nationally).
The GPU includes a Wildlife Corridor Map (Figure CR-3), which identifies the Puente-Chino Hills Wildlife Corridor, Major Wildlife Movement Corridors, and also City of Brea
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provides a connectivity ranking (from 1 to 5) for lands along the corridor. Figure CR-3 should be updated to address the following key issues:
1) Major Wildlife Movement Corridors identified as a narrow brown line is misleading. In fact, animal movement is not necessarily along a line but rather broad movement areas. The corridors shown do not appear accurate based on decades of collecting data. For example, wildlife does not travel along Carbon Canyon Road where vehicular traffic would be a constant source of noise and danger. When they have other options, animals generally do not choose to go through a housing development like the map depicts in Olinda Village and the line more accurately belongs farther to the east.
Animals do not travel along Telegraph Canyon in Chino Hills State Park on the same dirt road with cyclists and hikers, as is depicted. As an example, Dr. Paul Beier’s mountain lion study from the mid-1990’s tracked a single animal as it traversed the Puente-Chino Hills Wildlife Corridor (see Exhibit C) and Hills For Everyone has plotted data for M317, a single cougar tracked in 2023 (Exhibit D). Figure CR-3 should be updated with more local information on major movement corridors.
2) Where wildlife cross a road is critically important and missing from the map.
There are no cameras along roadways, so the only way we know where they cross is where they are killed. Hills For Everyone has nearly 50 years of observation and photos for Carbon Canyon Road, and the data shows that wildlife cross at the areas shown as circles on the map included as Exhibit E. Other relevant data could come from Caltrans, Orange County Animal Control Services, or The Road Ecology Center run by Dr. Fraser Shilling at UC Davis. Wildlife Crossing information should be reflected on Figure CR-3.
In addition to including more information to comply with AB 1889, the GPU should also clearly demonstrate compliance with Senate Bill (SB) 1425, which mandates that the General Plan include plans and action programs that address:
1) Equitable access to open space, considering social, economic, and racial equity; 2) Climate resilience and other benefits coordinated with the Safety Element; and 3) Rewilding opportunities to preserve and enhance natural ecosystems.
Specific actions proposed to address these requirements are identified below (in underline). Brea’s General Plan already includes those goals, policies, and actions that are not underlined:
Existing CR Goals
CR-3: The preservation and maintenance of open spaces for nature, resource management, recreation, and scenic enjoyment.
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CR-4: A community where visual resources reflect Brea’s natural beauty and help guide responsible development.
CR-5: A resilient ecosystem that safeguards habitats for biological resources and wildlife.
Existing CR Policies
CR-3.1: Open Space Preservation. Continue efforts to preserve open space lands for purposes of habitat protection, resource conservation, flood hazard management, public safety, and overall community benefit in collaboration with neighboring jurisdictions and other relevant agencies.
CR-3.2: Sensitive Species and Habitats. Support the conservation of sensitive species, plant communities, and wildlife habitats to the maximum extent feasible through open space dedication, creative site design, and other workable actions.
CR-3.3: Hillside Preservation. Continue efforts to conserve sensitive hillside, ridgelines, canyons, and open space areas in accordance with standards set forth in the Brea City Code.
CR-3.4: Mature Vegetation. Encourage all entities involved in development, redevelopment and landscape maintenance to avoid removing mature vegetation.
Promote the inclusion of a variety of sizes of new vegetation in projects to balance initial aesthetic landscape value with the long-term health and sustainability of the landscape.
CR-3.5: Rewilding. Explore rewilding opportunities and other ecological restoration projects aimed at increasing biodiversity and restoring natural processes.
CR-3.6: Open Space Education. Work with State, Federal, and community partners to develop educational and other materials that promote the preservation and conservation of Brea’s natural resources, to the extent practical.
CR-5.7: Wildlife Corridors. Encourage the preservation of critical wildlife corridors and habitat connectivity, including as part of the development review process.
CR-5.8: Urban Canopy. Preserve and expand the urban canopy of trees and vegetation throughout the community to help reduce urban heat, improve air quality, reduce stormwater runoff, enhance aesthetics, and support biodiversity.
Existing CR Actions
CR-3a: Assess development proposals for potential impacts to important geologic and scenic landform features pursuant to the California Environmental Quality Act (CEQA). Require appropriate mitigation measures, including environmentally sensitive site planning and grading, revegetation and open space dedication, for significant impacts. Consider important topographical features, watershed areas, City of Brea
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ridgelines, soils, and potential erosion problems in the assessments. Ensure the new development is compatible to adjacent open space lands.
CR-3b: Reassess the City’s Hillside Zoning Ordinance to minimize the encroachment of new development near areas of open space, especially sensitive areas.
CR-3c: Collaborate with Federal, State, regional, local, non-profit environmental and conservation organizations, and private entities to conserve, protect, and enhance open spaces and natural resources throughout Brea’s Planning Area.
CR-4a: Assess development proposals, including those in Brea’s SOI, for potential impacts to important visual resources pursuant to CEQA. Require appropriate mitigation measures for all significant impacts. Consider important ridgelines, creeks, open space, views of the surrounding hillsides, and light and glare effects.
CR-4b: Maintain and apply existing design standards to preserve views, vistas, and defining natural features along prominent roadways and visually sensitive areas.
CR-5a: Maintain a buffer area between natural waterways and urban development to protect water quality and riparian areas, as deemed necessary.
CR-5d: Work with local, regional, State and Federal partners to seek funding for wildlife corridor improvements such as dry wedges, culverts, overcrossings at priority locations with high instances of roadkill.
CR-5e: Evaluate the potential to implement a Dark Sky ordinance or other similar regulatory mechanism.
CR-5f: Continue to maintain the City’s tree inventory and use it to periodically identify areas where the urban canopy can be expanded and prioritize these areas for new tree plantings. Establish an inventory-based citywide street-tree lifecycle program with the following elements:
• Prune street trees on a 3–5 year cycle and reserve annual funds for removal/succession planting with the goal of a “No Net Loss” urban canopy standard.
• Establish a citywide tree canopy target. The target measurement should be set to be a measurable improvement over existing conditions and should establish annual planting quotas to meet the target.
• Prioritize street tree planting in the census tracts identified as low-income on Figure CD-5, with annual Council reporting.
• Require tree replacement ratios of greater than 1:1 for both public and private property street tree removals.
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Proposed Additional Actions:
Limit the extension of public services and utility infrastructure into the City’s SOI (water, sewer, roadways) to reduce increasing fire risks and minimize other environmental impacts.
Establish standard conditions of approval (or establish and apply Wildlife Overlay Zoning) to subdivision/zoning approvals to require measures that will help ensure the implementation of measures to maintain connectivity and permeability for wildlife movement. There are many useful standards that should be adopted, including:
• Cluster development, including building pads and driveways, to minimize the perimeter edge of the neighborhood. Require the remainder of the parcel to be protected in an open-space/conservation easement that connects to off-site open space; no fences, structures, night lighting, or turf within the easement area;
• Dark-Sky Lighting. Full cutoff, motion-activated where feasible; 0.1 footcandle maximum at the open space border.
• Bird-Safe Design. For façades within 300 ft of open space, treat at least 90% of glazing with patterns, and prohibit reflective glass.
• Mechanical Noise. Locate HVAC/pool equipment away from open space and enforce a maximum noise volume of 45 dBA at the property line. • Wildlife-Permeable Fuel Modification Plans. Wildfire-safe fuel modification zones must maintain visual cover (allow patches 2-3 feet in height) and avoid complete denudation.
• Establish standards for wildlife-safe barriers and fencing adjacent to open space that requires a minimum of 50% permeable fencing (no continuous solid walls) with a minimum of 6 inches of ground clearance and that restrict grading/retaining walls that block known wildlife corridors.
Require that any project proposed within an identified wildlife movement corridor shall be subject to a Wildlife Movement Impact Analysis prepared by a qualified wildlife biologist, demonstrating that the project will maintain or enhance corridor function.
Identify and prioritize locations where roads, drainage channels, and other linear infrastructure fragment wildlife movement corridors within the City limits or SOI.
The City shall: (a) include wildlife crossing feasibility in all future road design, improvement, or reconstruction projects on roads crossing or adjacent to identified wildlife corridors; (b) require development projects that widen or realign roads in City of Brea
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corridor areas to fund wildlife crossing infrastructure proportional to their impact; and (c) coordinate with Caltrans on SR-57 and SR-142 crossings.
Require that all fuel modification plans within mapped Fire Hazard Severity Zones (FHSZs) be prepared to: (a) map all sensitive vegetation communities within the proposed fuel modification zone; (b) identify the minimum modification footprint necessary to achieve the required fire protection standard for each zone band; (c) specify that native, fire-resistant, locally-appropriate species be used in all replanting areas; and (d) demonstrate that the cumulative habitat removal for the project does not exceed the minimum necessary to achieve the adopted fire protection standard.
When resurfacing or replacing culverts within known wildlife corridors or habitat linkages, upgrade to wildlife-passable crossings and add guiding fencing and native vegetation.
Ensure that at least 90% of residents live within a 10-minute walk (½ mile) of a park or publicly accessible open space, prioritizing disadvantaged or under-served neighborhoods or census tracts identified as low-income on Figure CD-5.
Require universal design, wayfinding, shade/heat relief, and fee-free programming in communities with the greatest park gaps.
In addition to identifying additional public open space in the City’s denser areas as development intensifies, prohibit conversion of parks/open space serving disadvantaged or under-served neighborhoods without replacement of equal or better quality/access so that there is no net loss of community open space.
Prioritize nature-based solutions (floodplain reconnection, wetland/creek restoration, urban tree canopy, cool pavements) to minimize/mitigate flood, heat, wildfire, and drought risks. (Cross-reference to Public Safety Element) Establish a Rewilding and Ecological Restoration Program that identifies, prioritizes, and implements habitat restoration projects on public and private lands to increase biodiversity, restore native species, and reconnect fragmented ecosystems.
Specify locally native, drought-tolerant plant palettes; prohibit invasive species in public landscapes; encourage reintroduction of keystone/native pollinator habitats where feasible. No trees or other plant species that are on the California Invasive Plant Council (Cal-IPC) Invasive Plant list or on their “watch list” for invasiveness are permitted.
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C. Policy Direction in the Public Safety (PS) Element.
The Public Safety Element has a section on Climate Change and Resiliency Planning, which recognizes that the City of Brea can implement policies at the local level to help the community adapt to climate change. See GPU at 211. However, the City must adopt further policies and actions for it to create “A community resilient to changing environmental patterns, including severe weather events and other adverse effects on public health, well-being, and safety,” as stated by Goal PS-5.
Hills For Everyone’s concerns about the issues covered in the PS Element are as follows:
• Urban tree canopy is mentioned but no quantified target is provided. The GPU sets no specific canopy coverage goal, no urban heat island reduction target, and no implementation program with budget or timeline for expanding the tree canopy.
Urban greening can be a significant climate resilience tool. • The GPU mentions maximum feasible beneficial use of stormwater, but there are no green infrastructure standards for new development (e.g., minimum bioswale or permeable paving requirements), no LID requirements beyond baseline NPDES, and no policy explicitly linking stormwater management to climate adaptation. • No urban cooling targets or standards for heat island mitigation. Given the intensity of Southern California heat events and the documented urban heat island effect in developed flatlands adjacent to natural areas, the plan should include cool pavement, cool roof, and urban shade standards for new development. • Climate-adaptive landscaping is not sufficiently specified. The GPU requires “native, non-invasive landscaping” but does not require climate-adaptive species selection, does not address phasing out non-native turf, and does not connect landscaping requirements to the water supply assessment (PEIR Appendix M) or to expected future precipitation variability.
Existing PS Policies
PS-1.10: Standards for New Development. Require ongoing brush management, fuel management/modification defensible space, fire resistant landscaping, visible home and street addressing and signage, and other project design features for new development located in High and Very High Fire Hazard Severity Zones as part of the review process.
PS-2.2: Hillside Development. In areas subject to the City’s Hillside Zoning Ordinance, require a full site-specific geologic study to consider effects of the proposed development on adjacent upslope and downslope areas as well as on the site itself.
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PS-3.9 Open Space Area. Preserve open space areas for flood mitigation when possible.
PS-5.11: Extreme Heat Vulnerabilities. Encourage new developments, major remodels, and redevelopments to address urban heat island issues and reduce urban heat island effects for the proposed project site and adjacent properties.
PS-6.6 Emergency Evacuation Routes and Access. Work with the Fire Department and Police Department to define minimum standards for evacuation of residential areas, particularly in HFHSZs and VHFHSZs, and to maintain, update, and regularly exercise emergency access, protocols, and evacuation routes to assess their effectiveness under a range of emergency scenarios. If areas with inadequate evacuation routes are identified develop appropriate mitigation measures, improvement plans, or education programs to ensure safe evacuation.
Existing PS Actions
PS-1d: Assess site constraints when considering land use designations near wildlands to avoid or minimize wildfire hazards as part of a land use update or amendment.
PS-6g: When evaluating public safety impacts of new developments, the methodology shall consider the following at minimum; however, the City may allow alternate methodology on a case-by-case basis:
• Service Demand Units (SDUs) estimated by land-use type and intensity • Population/employee growth and special risk factors (e.g., WUI, hazardous occupancies, vertical development)
• Network travel-time isochrones and station coverage impacts relative to public safety Service Level Objectives (SLOs)
• Unit-Hour Utilization (UHU) and workload balancing by company • Facility/apparatus/staffing triggers when thresholds are exceeded Proposed Additional Actions:
Adopt a Heat and Air Quality Improvement Plan that contains:
• Cool Pavement standards and pavement resurfacing with shade tree/street tree planting quotas per linear mile.
• Cooling networks with shaded routes and designated cooling centers. • Subsidies or incentives for cool walls and cool roof retrofits. • Methods to integrate metrics for minimizing heat impacts into capital improvement programming.
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III. The Draft Program EIR Biological Resources Mitigation Measures Must Be Strengthened.
The PEIR’s finding of potentially significant impacts obligates the City to adopt legally adequate mitigation measures, and CEQA requires all mitigation measures be adopted simultaneously with, or prior to, Project approval. Mitigation measures may not be deferred when their effectiveness is uncertain or when deferral would prevent the EIR from disclosing the potentially significant impacts of those measures. Sacramento Old City Ass’n v. City Council of Sacramento, 229 Cal.App.3d 1011, 1027-29 (1991).
Uncertainties regarding the mitigation of impacts must be resolved before a lead agency may make the required CEQA findings; an agency may not rely on mitigation measures of uncertain efficacy or feasibility. Kings County Farm Bureau v. City of Hanford, 221 Cal.App.3d 692, 727 (1990). An agency may defer preparation of a plan or completion of a study only when the agency commits itself to satisfying specific performance standards that will ensure avoidance of any significant effects. Id.
Several of the proposed mitigation measures in this PEIR need additional specificity and performance standards to ensure they are fully enforceable and effective at reducing impacts to less-than-significant levels; particularly with respect to wildlife connectivity and hillside habitat areas. The following recommendations are offered to strengthen the clarity, enforceability, and ecological effectiveness of the mitigation framework.
A. Clarify and Strengthen Pre-Construction Survey Requirements.
Mitigation measures requiring pre-construction biological surveys (MM BIO-1, -2, -3, -6, and -7) should be revised to establish minimum survey protocols, including: 1) the specific types of surveys that are required (general biological survey, focused species surveys, jurisdictional delineations), and 2) identifying seasonal timing requirements tied to species detectability. The measures should also specifically require that surveys be conducted prior to any site disturbance, including grading, vegetation clearing, or fuel modification (as opposed to the current “before construction” language that exists in some measures), require that survey results be documented in a report submitted to and approved by the City prior to issuance of grading permits, and, where sensitive resources are identified, the measures should require mandatory avoidance and minimization to the maximum extent feasible, rather than leaving such determinations to later discretionary judgment.
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B. Establish Clear Performance Standards for Habitat Protection and Replacement.
Where impacts to sensitive habitats (e.g., riparian areas, coastal sage scrub, or other native vegetation communities) may occur, mitigation measures should be revised to include: 1) quantifiable mitigation ratios (e.g., 2:1, 3:1, or higher depending on habitat sensitivity); 2) clear requirements that mitigation lands be located within the same ecological region, functionally equivalent or superior in habitat value, and protected in perpetuity through conservation easements or similar mechanisms; and 3) metrics for evaluating the success of restoration efforts that include the minimum amount of native plant cover and the required monitoring duration (e.g., 5–10 years or until success criteria are met).
C. Strengthen Measures Protecting Wildlife Movement and Connectivity.
To ensure the long-term preservation of wildlife movement and connectivity corridors, MM BIO-1 should be revised to more clearly detail the requirements of “an evaluation of potential local and regional wildlife movement corridors” (PEIR at 4.3-60).
The measure should specifically require that discretionary projects avoid siting development within identified or potential wildlife movement corridors to the maximum extent feasible. Where avoidance is not feasible, the measure should require maintenance of minimum corridor widths based on best available science, the use of wildlifepermeable fencing (e.g., avoidance of solid walls), minimizing lighting adjacent to corridors, and the installation of wildlife overcrossings or properly-sized undercrossings where roads intersect movement areas.
D. Limit Reliance on Future Discretionary Determinations.
Several mitigation measures currently rely on phrases such as “if determined necessary” or “as appropriate.” While some flexibility is appropriate at the program level, the measures would be strengthened by identifying specific triggers for when mitigation is required and defining minimum required actions. Furthermore, to ensure long-term effectiveness, mitigation measures should include any ongoing monitoring requirements, annual reporting to the City if appropriate, and adaptive management provisions, requiring corrective actions if the performance standards identified in the mitigation measures are not met. By incorporating clear performance standards, reducing reliance on future discretionary determinations, and strengthening protections for wildlife connectivity—particularly in hillside areas—the City can enhance both the environmental outcomes and the overall defensibility of the PEIR.
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In addition to the points raised above regarding the mitigation measures, we also point out two corrections that should be made to PEIR Figure 4.3-5 (Wildlife CorridorNCCPs Map): the Shell/Metropolitan Water District HCP and the Orange County Transportation Authority NCCP/HCP should both be added to the figure. A map of the Shell/MWD HCP is included as Exhibit F and the OCTA NCCP/HCP is included as Exhibit G.
IV. Conclusion
The proposed GPU and BCSP are an important opportunity for Brea to commit to actively discouraging development in hillside areas within the Brea’s Sphere of Influence, emphasizing both fire safety and wildlife protection at the urban edge, bringing the General Plan into compliance with new State laws that prioritize wildlife corridors and habitat connectivity, and supporting urban greening and climate resiliency. The development envisioned in the GPU and BCSP will have significant impacts, and implementing the policy suggestions and mitigation measure revisions in this letter will serve to ameliorate those effects and provide a benefit to all of Brea.
Please notify Hills For Everyone and this office of the release of the Final GPU/BCSP and the Final PEIR, and provide us all notices for any hearings, staff reports, briefings, meetings, and other events related to the Project.
Respectfully yours,
SHUTE, MIHALY & WEINBERGER LLP
Edward T. Schexnayder
cc: Claire Schlotterbeck, Hills For Everyone
Exhibits:
A: Confirmation receipt of September 24, 2025 NOP comment letter submittal.
B: Maintaining Ecological Connectivity Across the “Missing Middle” of the PuenteChino Hills Wildlife Corridor, prepared by Dr. Wayne D. Spencer of the Conservation Biology Institute (2005).
C: Coordinates for Cougar Tagged M6, prepared by Dr. Paul Beier, exhibit prepared by Hills For Everyone.
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D: Plotted Data Points for Cougar Tagged M317.
E: Locations of Wildlife Crossing Fatalities, prepared by Hills For Everyone.
F: Shell/Metropolitan Water District HCP map.
G: Orange County Transportation Authority NCCP/HCP map. 2045394.1
Exhibit A
1 Kristi Bascom
From: Brea2050 <[email protected]>
Sent: Wednesday, September 24, 2025 8:46 PM
To: Kristi Bascom
Cc: [email protected]; Schlotterbeck, Claire; Edward T. Schexnayder; Brea2050 Subject: RE: CEQA Comments for Brea 2050: Focused GPU and BCSP Hello,
This is to acknowledge the receipt of the NOP comments.
Thank you.
Sincerely,
Community Development | Planning
P: 714-990-7674 | E: [email protected] | W: www.brea.generalplan.org City of Brea | 1 Civic Center Circle | Brea, California 92821 The City Hall is closed alternating Fridays.
Please click 2025 Calendar for City Service Hours/Alternate Fridays Closed.
From: Kristi Bascom <[email protected]>
Sent: Wednesday, September 24, 2025 2:06 PM
To: Brea2050 <[email protected]>
Cc: [email protected]; Schlotterbeck, Claire <[email protected]>; Edward T. Schexnayder <[email protected]>
Subject: CEQA Comments for Brea 2050: Focused GPU and BCSP Dear City of Brea Planning StaƯ,
On behalf of our client, Hills For Everyone, we submit the attached comment letter on the Notice of Preparation (NOP) for the forthcoming EIR on the City of Brea’s Focused General Plan Update (GPU) and Brea Core Specific Plan (BCSP).
2 Please confirm that this email has been received and inform me directly if you have any trouble accessing the attached PDF.
Kind regards,
Kristi Bascom
Kristi Bascom, AICP
Urban Planner
Shute, Mihaly & Weinberger LLP
396 Hayes Street
San Francisco, CA 94102-4421
o: 415/552-7272 x 202 c: 925/872-6327
www.smwlaw.com | A San Francisco Green Business
Exhibit B
Maintaining Ecological Connectivity
Across the “Missing Middle”
of the
Puente-Chino Hills Wildlife Corridor
Final Report
July 2005
The Conservation Biology Institute provides scientific expertise to support conservation and recovery of biological diversity in its natural state through applied research, education, planning, and community service.
Maintaining Ecological Connectivity
Across the “Missing Middle”
of the
Puente-Chino Hills Wildlife Corridor
Final Report
Prepared by:
Wayne D. Spencer, Ph.D.
815 Madison Avenue
San Diego, CA 92116
Prepared for:
Resources Legacy Fund Foundation
555 Capitol Mall, Suite 650
Sacramento, CA 95814
July 2005
Puente-Chino “Missing Middle” Analysis
Conservation Biology Institute ii July 2005
Table of Contents
Page
Acknowledgements ................................................................................................................ iv Executive Summary.................................................................................................................v Methods................................................................................................................................v Results............................................................................................................................... vii Discussion.......................................................................................................................... ix Conclusions and Recommendations ....................................................................................x Introduction..............................................................................................................................1 Report Objectives.................................................................................................................2 Study Area ................................................................................................................................4 Biogeography.......................................................................................................................4 Previous Studies...................................................................................................................4 Methods...................................................................................................................................10 Reconnaissance..................................................................................................................10 Target Species....................................................................................................................11 Defining Geographic Units, Barriers, and Filters ..............................................................14 Analyses — Assessing Existing and Future Functionality................................................18 Results .....................................................................................................................................20 Functionality of Geographic Units.....................................................................................20 Summary of Overall Corridor Function.............................................................................31 Future Corridor Functions..................................................................................................35 Discussion................................................................................................................................40 Functions and Benefits of Wildlife Corridors....................................................................40 Assessing Connectivity Pros and Cons..............................................................................40 Mitigating Road Effects.....................................................................................................43 Conclusions and Recommendations.....................................................................................45 Conservation and Restoration Priorities for the Missing Middle ......................................45 References Cited.....................................................................................................................49 Puente-Chino “Missing Middle” Analysis
Conservation Biology Institute iii July 2005
Page
Maps
Map 1. Study area showing the Missing Middle of the Puente-Chino Hills Wildlife Corridor................................................................................................3 Map 2. Geographic units of the Puente-Chino Hills Wildlife Corridor……………... 15 Map 3. Conservation and restoration priorities in the vicinity of Missing Middle...... 46 Figures
Figure 1. The Puente-Chino range of hills juts into the heavily urbanized Los Angeles Basin from the tip of the Santa Ana Mountains range……………………...… 1 Figure 2. View northwest across Coal Canyon Wildlife Underpass…......................... 23 Figure 3. View northeast across Tonner Bridge and Highway 57…………………….. 25 Figure 4. View northwest across Segment 3 and Harbor Boulevard to Segment 4, indicating general trends in wildlife movements……………………………. 27 Figure 5. Conceptual development plan for the Shell-Aera Master Planned Community………………………………………………………………… 35
Figure 6. Aerial photograph showing City of Industry’s proposed Tres Hermanos reservoir and new road in Tonner Canyon…………………………………... 37 Photos
Photo 1. View east under the Tonner Bridge…………………………………………. 26 Photo 2. View southeast across the Harbor Boulevard “deathtrap”…………………. 28 Tables
Table 1. Summary of previous studies of wildlife populations and movements in the Puente-Chino Hills study area………………………………………………... 5
Table 2. Characteristics of geographic units comprising the Puente-Chino Hills Wildlife Corridor……………………………………………………………. 21
Table 3. Characteristics of roads crossing the Puente-Chino Hills Wildlife Corridor... 22 Table 4. Functional classification of geographic units for supporting target species populations and movements…………………………………………………. 33
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Acknowledgements
Conservation Biology Institute (CBI) thanks the following individuals and organizations for support and contributions to this report. Financial support was provided by Resources Legacy Fund Foundation, with special thanks to Maureen Rose and Ed Hastey. Rick Rayburn (California State Parks) was responsible for involving CBI in this important project and provided early guidance on its goals. Claire Schlotterbeck (Hills For Everyone) provided essential information, advice, contact information, and inspiration, and Melanie Schlotterbeck (The Trust for Public Land) provided GIS data, photographs, advice, information, contacts and other valuable input. Dan Wooldridge (Waters and Faubel) provided copies of various reports and plans reviewed in this report. Andrea Gullo and Amy Henderson (Puente Hills Landfill Native Habitat Preservation Authority) also provided data, reports, and other useful information. Geary Hund, Claire Schlotterbeck, Melanie Schlotterbeck, and Amy Henderson reviewed a draft of this report and offered valuable corrections and clarifications to the contents. The following CBI employees assisted in preparing this report: Heather Rustigian, with oversight from Jim Strittholt, prepared GIS maps and calculations; John Bergquist provided Keyhole screen captures used as illustrations; and Mike White and Jerre Stallcup reviewed and helped produce the report.
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Executive Summary
The Puente-Chino Hills Wildlife Corridor is a peninsula of mostly undeveloped hills jutting about 42 km (26 miles) from the Santa Ana Mountains into the heart of the densely urbanized Los Angeles Basin. Intense public interest in conserving open space here has created a series of reserves and parks along most of the corridor’s length, but significant gaps in protection remain.
These natural habitat areas support a surprising diversity of native wildlife, from mountain lions and mule deer to walnut groves, roadrunners, and horned lizards. But maintaining this diversity of life requires maintaining functional connections along the entire length of the corridor, so that wildlife can move between reserves—from one end of the hills to the other.
Already the corridor is fragmented by development and crossed by numerous busy roads, which create hazards and in some cases barriers to wildlife movement. Proposed developments threaten to further degrade or even sever the movement corridor, especially within its so-called “Missing Middle.” This mid-section of the corridor system, stretching from Tonner Canyon on the east to Harbor Boulevard on the west, includes several large properties proposed for new housing, roads, golf courses, and reservoirs. Such developments would reduce habitat area and the capacity to support area-dependent species and, if poorly designed, could block wildlife movement through the corridor.
This report builds on an impressive array of previous ecological and wildlife movement studies in the Puente-Chino Hills, as well as the general literature on wildlife movement corridors as it applies to this unique peninsula of wildness. It supplements the existing information with an analysis of gaps in protection—with special focus on the vulnerable Missing Middle—and recommends conservation and management actions to prevent further loss of ecological connectivity and retain native species.
Methods
I performed a meta-analysis of corridor function using existing scientific information on the distribution and movement patterns of wildlife species in the study area, as supplemented by field reconnaissance and examination of aerial and satellite imagery. Following the lead of previous researchers, I segmented the range of hills into nine geographic units by roads and other breaks in habitat contiguity. From southeast to northwest these are:
• A biological “core” area (defined below), represented by the Santa Ana Mountains; • Seven segments of the functional Puente-Chino Hills Wildlife Corridor (from southeast to northwest: 1-Chino, 2-Carbon-Tonner, 3-Shell-Aera, 4-Powder-Schabarum, 5-San Miguel, 6-East Whittier, 7-West Whittier); and
• One isolated patch off the tip of the range of hills (Whittier Narrows), which is effectively disconnected from the functional corridor segments by major roads and urban barriers.
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The Missing Middle consists of the western portion of Segment 2 (including the large and biologically diverse Tonner Canyon) and all of Segment 3 (Shell-Aera property and adjacent lands between Highway 57 and Harbor Boulevard). The eastern portion of Segment 2 (between Tonner and Carbon Canyons) is largely conserved already, but Tonner Canyon and Shell-Aera are unprotected and threatened by development projects.
Each of the nine geographic units was initially characterized for how it appears to function in supporting populations of target species, including mountain lion, mule deer, bobcat, coyote, coast horned lizard, and greater roadrunner, as well as in the richness of its reptile and amphibian community. The following coarse-scale definitions apply to these units:
• Core areas must be larger than 2,000 sq. km and capable of supporting a population of 20 adult mountain lions (the most area-dependent target species). Due to large size and relatively low “edge effects,” a core area will support the greatest diversity of species and should support populations of all target species. The Santa Ana Mountains are the only core in the study area. This core serves as a source for mountain lions and other species to enter the corridor system.
• Subcores are smaller (but at least 60 sq. km) and capable of supporting a population of bobcats, the second-most area-dependent target species. Subcores can sustain populations of most target species and have moderate to high species diversity. Corridor Segment 1 (Chino Hills between Highways 91 and 142) is the only subcore, although Segment 2 appears to function as an extension of this subcore, as discussed below. • Patches are smaller than 60 sq. km, but may support small numbers of bobcats and significant populations of other target species. Patches may also provide significant livein or move-through habitat for mountain lions and bobcats, whose home ranges may cover multiple geographic units. Most segments in the corridor system are patches, but they vary greatly in size (from about 1.5 to 44.3 sq. km), vegetation composition, isolation by roads, and ability to support target species.
The roads delimiting these segments were next characterized for their effects on target species movements—as barriers, semi-permeable “filters,” or highly permeable filters. Based on the scientific literature and field reconnaissance, each road was assessed for how easily target species can cross it, the availability and effectiveness of crossing structures (e.g., bridges and underpasses), and relative frequency of roadkill. Roads considered highly permeable to wildlife movement allow adjacent segments to function as one larger segment, such that two areas originally classified as separate patches may effectively serve as one larger patch (summing the area of adjacent units), or even a subcore, for certain target species.
I assigned each newly defined unit, or composite unit, a function relative to supporting individuals or populations of each target species based on unit size, habitat composition, and other factors, as follows:
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• Population — capable of supporting a breeding population of at least 20 adults and potentially serving as a source of individuals that disperse into other units. • Subpopulation — capable of supporting at least two but less than 20 breeding individuals.
Subpopulations may exchange individuals with other areas within a larger metapopulation (a set of partially isolated populations linked by occasional dispersal) and may provide individuals to recolonize habitat patches in case of local extirpation. • Home Range Part — incapable of supporting at least two breeding individuals on its own, but may provide live-in habitat (e.g., foraging or resting cover) and form a part of one or more individuals’ home range(s).
• Move-through — not contributing significant live-in habitat for a species as part of a functional home range, but capable of accommodating movements between more substantial units within a home range, or potentially used for dispersal between other habitat units.
This system for characterizing geographic units and movement impediments was used to assess how the overall corridor system functions to support target species, and how these functions might change with potential development scenarios, such as new roads or housing that could add movement barriers or reduce wildlife carrying capacity in corridor segments.
Results
Existing Corridor Function
The Puente-Chino Hills Wildlife Corridor appears functional for at least larger mammals and birds, although tenuously so in the Missing Middle (due to several barrier or near barrier roads) and across smaller Segments 4 and 5 (due to their small size, strong edge effects, and high human and pet activity). Essentially all roads in the study area are considered barriers or at least strong filters to movements by many reptiles, amphibians, and small mammals; however, most birds and larger mammals currently can move between all segments either at-grade (with mortality risks) or via critical road-crossing structures. Despite many crossing constraints through the corridor, especially in and just west of the Missing Middle, target species are confirmed or highly likely to occur in all seven Puente-Chino Hills corridor segments, except for coast horned lizard, which may already be absent (or will disappear in the future) west of Highway 57.
Individual mountain lions are capable of traversing the length of the corridor, albeit at some risk of roadkill, and one or more lions still hunt as far west as the western Puente Hills (known locally as the Whittier Hills). Most other target species (e.g., bobcats, roadrunners) appear to persist throughout the corridor as metapopulations that are connected genetically and demographically by at least occasional dispersal between geographic units.
Carbon Canyon Road (between Segments 1 and 2) and Turnbull Canyon Road (between Segments 6 and 7) are considered highly permeable to at least larger mammals and birds, so I Puente-Chino “Missing Middle” Analysis
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merged Segments 1 and 2 to form a larger Chino-Tonner subcore, and I merged Segments 6 and 7 to form a larger Whittier Hills patch. The most critical road-crossing structures are the Coal Canyon Wildlife Underpass (connecting the Santa Ana Mountains Core to the Chino Hills under Highway 91); a box culvert under Carbon Canyon Road known to be used by bobcat and other species; the Tonner Canyon Bridge on Highway 57 (the only viable crossing beneath this busy freeway for deer, mountain lion, bobcat, and other species); and the Colima Service Tunnel (used by bobcat, deer, coyote, and other species to cross under Colima Road between San Miguel Canyon and the Whittier Hills). In addition, a new wildlife tunnel is being built under Harbor Boulevard (between Segments 3 and 4) at a location well-documented as a roadkill “death trap.” There appears to be a gradient of declining amphibian and reptile diversity and evenness moving west from the Chino Hills, probably due to increasing edge effects coupled with increasing distance and number of barriers and filters that must be crossed the farther west one moves from source habitats in the east. A similar gradient may exist for other taxa, such as small mammals, that are similarly limited in their dispersal abilities.
Given the length of the corridor relative to species movement abilities, the capacity of corridor segments to support many species depends both on
• The potential for individual movement between each set of adjoining segments (a function of roads and road-crossings), and
• Having sufficient live-in habitat along the way to support populations or subpopulations that contribute dispersing individuals.
The greater a segment’s distance from units supporting populations or subpopulations of a species, the lower the probability that the segment can continue supporting a species. If the distance between occupied segments becomes too great, or if barriers prevent inter-segment movement, local extinctions are inevitable in the isolated segments. Thus, any reduction in the capacity of segments to support populations or subpopulations increases the probability of local extinctions in that segment, as well as in all other “downstream” segments to the west.
Habitats in the Missing Middle are critical to maintaining overall corridor function. The Tonner Canyon area serves as an extension of the large Chino-Tonner subcore, with significant live-in habitat that can contribute dispersing animals to move into other segments. Likewise, Segment 3 (Shell-Aera) presumably supports significant numbers of target species that disperse (currently at some risk) across Harbor Boulevard into Powder Canyon (Segment 4) and beyond.
Future Scenarios
I assessed the likely effects of several proposed development projects in the Missing Middle on species persistence through the corridor system. This qualitative assessment uses the conceptual model developed above, based on how projects might affect the capacity of geographic units to support populations or individuals and the ability of individuals to cross between units. The projects include a new residential community, a series of reservoirs, and a major new road.
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All three proposed developments have the potential to extirpate target species from large portions of the Puente-Chino Hills Wildlife Corridor. By impeding species movements or metapopulation dynamics, a project’s impacts on species persistence may extend far beyond project boundaries, potentially rippling through the range of hills to eliminate wildlife populations as far west as the Whittier Hills (10-12 km west of the Missing Middle). The proposed Shell-Aera Master Planned Community would seriously degrade the ability of Segment 3, and all segments farther west, to support target species, especially mountain lion and bobcat.
This would have cascading effects on flora and fauna in all segments from this point west.
A plan by the City of Industry to build three water reservoirs in Tonner Canyon could also have substantial adverse impacts on corridor function. Although a reservoir or other development in upper reaches of Tonner Canyon might not greatly affect corridor function, any development in middle and especially lower Tonner Canyon could have severe impacts on corridor function, especially if wildlife use of the Tonner Canyon Bridge (to cross Highway 57) is reduced. Any development that blocks access through the bridge area would make Highway 57 a complete barrier to many species and would likely lead to wildlife extirpations in segments farther west.
At the very least, creation of these reservoirs would reduce the size of the Chino-Tonner subcore and its capacity as a source of animals that disperse into the rest of the corridor system.
Finally, plans by the City of Industry to build a new road running the length of Tonner Canyon could split the Chino-Tonner subcore in two, potentially isolating about 21.2 sq. km of habitat from this currently large and contiguous source habitat. The road would probably require major cut and fill to construct and could render disfunctional the critical Tonner Bridge wildlife undercrossing. This would almost surely result in the rapid loss of mountain lion and bobcat from more westerly segments, with cascading effects through the ecological community. Deer and other species would also likely disappear from westerly segments over a longer time period.
A full impact analysis for any of these proposed projects should address cumulative impacts on wildlife populations and movements through the corridor. Among these cumulative impacts would be inducement of further development, such as additional residential, commercial, or industrial development along the road. Increases in traffic and roadkill should also be analyzed and mitigated for. Any combination of two or more of these projects, even if well designed, would likely render the Puente-Chino Hills Wildlife Corridor non-functional west of Chino Hills State Park, regardless of mitigation.
Discussion
The scientific literature on the functions and values of wildlife corridors is huge and growing.
Movement corridors connecting reserves or larger “core areas” of habitat have been documented to counter many adverse effects of isolation by fragmentation on species and ecological processes. Some critics have argued that there are costs as well as benefits to conserving corridors and that, under certain circumstances, creating or maintaining corridors could harm some species or communities. However, the overwhelming weight of scientific evidence is that maintaining connectivity is beneficial, especially for those species and ecological communities Puente-Chino “Missing Middle” Analysis
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for which connectivity “is the natural state of things.” Most arguments against corridors boil down to nothing more than cautions against viewing them as conservation panaceas.
Nevertheless, I reviewed the following arguments made against corridor conservation as they apply to the Puente-Chino Hills Wildlife Corridor:
1. Corridors may serve as conduits for the spread of deleterious species;
2. Corridors may spread detrimental processes, such as wildfire or disease, among reserve areas;
3. Corridors may facilitate movements by highly mobile and adaptable animals (like coyotes), but may not help more sedentary or at-risk species;
4. Corridors could attract wildlife into edge-affected habitats with high mortality rates; and
5. Corridor conservation may be more expensive or less beneficial than other options, such as increasing the size or management of core reserves.
Critical review of these concerns for the Puente-Chino Hills Wildlife Corridor finds them irrelevant or insignificant in this case; at least, the biodiversity benefits of conserving the corridor far outweigh any potential for harm.
Mitigating the adverse effects of roads, including barrier effects and increased mortality, is essential to maintaining corridor functions. The scientific literature on effective mitigation actions, especially wildlife road-crossing structures, is also large and growing, with many success stories. The main types of structures, from most to least effective, are vegetated landbridges (wildlife overpasses), bridges, underpasses, and culverts. Vegetated overpasses are quieter than underpasses, maintain ambient conditions, seem less intimidating for some species than dark tunnels, and have proven highly successful in the U.S., Canada, and Europe for a wide variety of wildlife species. Bridges are also highly effective, especially if wide and open with natural vegetation growing beneath, such as under the Tonner Bridge. Culverts and other tunnellike structures can be effective for some species, but only very large culverts (such as box culverts and equestrian tunnels) are effective for larger mammals. Earthen flooring is preferable to concrete or metal. Regardless of crossing type, wildlife fencing is crucial for keeping animals off the road and for funneling them toward the crossing structure. Vegetative cover near the entrances also increases wildlife use of crossing structures.
Conclusions and Recommendations
Given the huge investment already made to maintain the Puente-Chino Hills Wildlife Corridor, additional conservation investment in the Missing Middle seems not only prudent, but essential if society believes the continued presence of deer, bobcats, roadrunners, and other wildlife is desirable in this unique peninsula of wild in a sea of development. My recommendations for how to do this are largely concordant with previous recommendations by other biologists.
I recommend conserving all of Segment 3 (the Shell-Aera property) and at least the middle and lower portions of Tonner Canyon, including prohibiting any new road or other development that Puente-Chino “Missing Middle” Analysis
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would fragment this critical habitat block or degrade in any way the utility of the Tonner Bridge as a wildlife underpass. I also emphasize the following recommendations for improving roadcrossing structures and reducing roadkill.
A. Add wildlife fencing on either side of Carbon Canyon Road to reduce roadkill and encourage wildlife to use existing culverts, especially the concrete box culvert near the entrance to Chino Hills State Park. Add another wildlife crossing structure (bridge or vegetated over-crossing), designed to accommodate all large mammals, as mitigation for any future road upgrades.
B. Prohibit any development that would increase traffic under the Tonner Bridge or add any new impediments (structures, lights, noise, etc.) to the vicinity of the bridge. Restore riparian vegetation along Tonner Creek, where degraded by oil development activities.
Fence along Highway 57 if monitoring suggests road mortality is high.
C. Secure rights to install wildlife fencing along both sides of Harbor Boulevard to reduce roadkill and ensure maximum utility of the wildlife tunnel being built here. Plant screening vegetation on either side of the tunnel to provide cover to wildlife approaching the entrances.
D. Secure remaining “at-risk” parcels in the narrow, constricted portion of the corridor between Powder Canyon and Hacienda Boulevard. Enlarge or otherwise improve the existing equestrian tunnel under Hacienda Boulevard to enhance its use by wildlife, including adding screening vegetation on the western end. Add wing fencing on either side of the tunnel to help funnel wildlife to it. Do not fence extensively along Hacienda Boulevard, unless coupled with new crossing structures, because most large mammals currently cross at-grade. Consider building a wildlife overpass (a vegetated wildlife bridge) over Hacienda Boulevard, taking advantage of steep slopes rising up from either side of the road, as mitigation for any future road improvements that would increase traffic volume or speed.
E. Maintain and improve the Colima Service Tunnel as a critical wildlife underpass. Add fencing or screening vegetation if necessary, based on further site-specific inspection or monitoring. Limit actions that would increase disturbance in the vicinity of the Service Tunnel from sunset to sunrise, such as artificial lighting or nighttime traffic or recreational uses through the tunnel.
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This loss would be doubly unfortunate given the tremendous public investment already made to conserve and restore biological open space and unfettered wildlife movement through this range of hills—from the Coal Canyon wildlife underpass at Highway 91, through Chino Hills State Park, Powder Canyon, Schabarum Park, and other private and public open space dedications to the western end of the Puente Hills (known locally as the Whittier Hills1). According to the California Department of Parks and Recreation, nearly a quarter billion dollars have already been expended or committed to acquiring and restoring natural open space in the Puente-Chino Hills Wildlife Corridor (http://hillsforeveryone.org/state_investment_table.htm). But the benefits of these existing investments is severely threatened by proposed development projects— including new roads, housing developments, golf courses, and reservoirs.
These threats are most urgent in the so-called “Missing Middle” of the corridor—from Tonner Canyon on the east (mostly owned by the City of Industry) to Harbor Boulevard on the west (Map 1). No major reserves are yet established in this broad midsection of the Puente-Chino Hills, and connectivity is threatened by a major new housing development, a proposed road, and a series of new dams and reservoirs that would flood Tonner Canyon. Should one or more of these projects sever functional connectivity, reserves farther west (e.g., Habitat Authority Wilderness Preserve, Powder Canyon, and Schabarum Regional Park, among others) could lose key species and suffer further ecological degradation.
This report reviews available scientific evidence on wildlife movement corridors, reserve design, and local biological resources to define conservation priorities for maintaining connectivity from one end of the corridor to the other. It focuses on the Missing Middle, because this portion is least protected and is at most immediate risk of further degradation. The purpose of this analysis is to identify (a) those portions of the Missing Middle whose conservation would most contribute to continued wildlife movement and ecosystem health throughout the corridor system, and (b) remedial actions that would most improve the situation for native wildlife—such as retrofitting existing roads with wildlife crossing structures to reduce roadkill and improve movement opportunities.
Report Objectives
• Synthesize the science of wildlife movement corridors as it pertains to the Puente-Chino Hills Wildlife Corridor.
• Analyze existing conditions and potential future conditions for the persistence and movement of wildlife populations in the corridor system. • Recommend conservation and management priorities to sustain and improve connectivity through the Missing Middle and hence the greater Puente-Chino Hills Wildlife Corridor.
1 Although “Whittier Hills” is not an official geographic name recognized by the U.S. Geological Survey, the western portion of the Puente Hills is known locally as the Whittier Hills, and previous researchers have used this place name. I therefore also use Whittier Hills to refer to the hills west of Colima Boulevard.
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Map 1. Study area showing the Missing Middle of the Puente-Chino Hills Wildlife Corridor.
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Study Area
This study considers two nested study areas (Map 1): the entire Puente Hills-Chino Hills Wildlife Corridor, extending about 42 km from the Santa Ana Mountains to the San Gabriel River, and the so-called “Missing Middle” of this larger landscape. The Missing Middle is that section of the Puente-Chino Hills Wildlife Corridor from Harbor Boulevard on the west to and including Tonner Canyon on the east. The Missing Middle is largely unconserved and is threatened by a variety of development projects.
Biogeography
The Puente-Chino Hills are the northernmost extension of the Peninsular Mountain Range, which begins in Baja California, Mexico. They are a topographic expression of the 500-km-long Whittier-Elsinore fault system, pushed up between the Whittier and Chino sections of this major slip-shear fault system. The geologically dramatic origins of the hills also contribute to their relatively undeveloped status, because steep slopes, earthquakes, landslides, tar pits, and active and former oil wells have tended to limit development, at least until recently.
The hills rise from the flat Los Angeles Basin, at less than 100 m (300 ft) elevation, to over 540 m (nearly 1,800 ft) at San Juan Hill. The regional climate is mild and Mediterranean, which contributes to the high diversity of species in coastal Southern California. Vegetation in the hills is a mosaic of open grasslands (which have been affected by grazing over the years), coastal sage scrub, chaparral, oak woodlands, riparian scrub, riparian woodlands, and rare California black walnut woodlands—a grossly under-protected resource that could be considered an “endangered habitat.” These communities support flora and fauna relatively typical of the biodiversity in Southern California—which is remarkable given that the hills are entirely surrounded by the largest urbanized area in the U.S.
Previous Studies
The Puente-Chino Hills represent one of the most closely scrutinized and intensively researched wildlife movement corridors in Southern California, if not North America. Its existence and importance are well appreciated by the local populace, with 53% of local residents having “heard of the wildlife corridor in the Puente Chino Hills area” and 83% in favor of maintaining the corridor (51% “strongly” supported this) (Decision Research 2003). The area’s flora, fauna, and ecological functions are well studied, with a number of intensive studies of wildlife distributions and movements covering all or substantial portions of the area (Table 1). In 1994 an entire scientific conference was focused on the biological functions and values of this unique range of hills (Natural Resources in the Puente Hills-Chino Hills Corridor: Implications for Land Use and Planning. A symposium at Whittier College, March 18-19, 1994)2 .
2 Abstracts of papers presented at this conference can be found at http://www.hillsforeveryone.org/PDF Files/whittier college symposium.pdf.
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Assess likely movement routes and constraints.
Entire PuenteChino Hills Wildilfe Corridor from the Santa Ana River to the San Gabriel River.
Field reconnaissance, walking the length of the corridor to assess likely movement routes and constraints. Incidental observations of wildlife sign and roadkill.
At least one pathway without complete obstruction existed for large mammals, from the Santa Ana River to the Whittier Hills, in 1994-95, but with several significant constraints. The most critical impediment was Harbor Blvd. and adjacent development. Movement across Interstate 605 to the San Gabriel River (Whittier Narrows Recreation Area) considered “highly improbable.” Conserve land to connect existing reserves (especially in the middle portions of the Corridor); restore native vegetation; retrofit undercrossings at problem roads, especially Harbor Blvd., with tunnels or bridges to reduce roadkill and improve connectivity for large mammals.
Noss et al. 1997
All vertebrate wildlife
Assess importance of Coal Canyon linkage to maintaining viable species populations in the Santa Ana Mountains and Puente-Chino Hills.
Entire PuenteChino Hills Wildlife Corridor and Santa Ana Mountains.
Literature review, field reconnaissance, and analysis of which species’ populations were likely to benefit from protecting and improving the Coal Canyon linkage and underpass.
Coal Canyon is the last viable linkage between the Chino Hills and Santa Ana Mountains. At least 21 vertebrate species have populations <500 individuals in the Puente-Chino Hills, and at least four of these have <50 breeding adults. Risks of extirpation from the hills would increase for all these species in the absence of the Coal Canyon corridor. The corridor also benefits species in the Santa Ana Mountains, especially the mountain lion and several grassland species. Mountain lion and bobcat would likely be the first species adversely affected by loss of the corridor.
Protect and restore a functional undercrossing at the Coal Canyon interchange with Highway 91. Remove pavement and restore natural soils, vegetation, and drainage through the undercrossing, and install wildlife fencing to funnel wildlife off the highway and through the underpass.
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Table 1. Continued. Conservation Biology Institute 6 July 2005 Reference Target Species Major Focus Study Area Methods Relevant Results Recommendations Haas and Crooks 1999, Haas 2000, Haas and Turschak 2002 Large and mediumbodied mammals
How landscape variables and underpass characteristics affect the distribution and relative abundance of target species in the study area, and the frequency of underpass usage by each species.
Entire PuenteChino Hills Wildlife Corridor, from Santa Ana River to Whittier Hills.
Field methods: scat transects, remote-triggered camera stations, and baited track stations. Statistical analyses:Correlated probability and frequency of species use with landscape variables (e.g., corridor width, % wild) and underpass characteristics.
Bobcat and long-tailed weasel were negatively associated with habitat fragmentation. Fragmentation was negatively associated with probability of underpass usage by coyote, bobcat, and long-tailed weasel, and negatively associated with the frequency of use by bobcat. Underpass dimensions were important in determining probability of use by deer and gray fox, and with frequency of use in coyote, gray fox, deer, and domestic cat, with more open underpasses used most. The amount of natural cover surrounding the underpass entrance was important for bobcat. Fencing and roadway dividers were most effective on coyote use of underpasses. Overall, the probability of an underpass being used depends primarily on landscape characteristics,
while its frequency of use depends primarily on underpass dimensions.
Bobcats are an excellent target species for conservation in the study area. Habitat acquisition and restoration should be concentrated in the narrowest portion of the corridor and at chokepoints along roadways. Existing underpasses should be surrounded by natural cover and use fencing to direct wildlife under the roadway. Future underpasses should be large and situated as far from residential areas as possible.
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Table 1. Continued. Conservation Biology Institute 7 July 2005 Reference Target Species Major Focus Study Area Methods Relevant Results Recommendations Cooper 2000 Breeding birds Determine distribution of breeding land birds to identify priority conservation areas.
Entire PuenteChino Hills Wildlife Corridor, from Santa Ana River to Whittier Hills.
Point counts and walking transects to determine presence/absence.
California gnatcatcher, cactus wren, and other rare or declining species documented in diverse locations. Greater roadrunner widespread but not common; most commonly observed in middle portions of the Corridor. California quail found throughout study area except smallest fragments. Burrowing owl apparently extirpated from the study area during the 1990s. Several areas of high-quality habitats supporting diverse avifauna identified.
Conserve three priority areas based on size, threats, and support of declining species: (a) coastal sage scrub in northern Brea and Yorba Linda (southern portion of Missing Middle); (b) extensive grassland and savannah south of Rowland Heights (northern portion of Missing Middle); (c) grasslands of upper Tonner Canyon (northeastern portion of Missing Middle).
PCR et al. 2000
General wildlife
Analyze the Puente Hills area as a Significant Ecological Area (SEA) recognized by the County of Los Angeles.
That portion of the study area within Los Angeles County, from the Whittier Narrows to Tonner Canyon.
No original field studies; review and analysis of existing information.
The area meets several designation criteria as an SEA, including that it is regionally important to many resident and migrating species, especially large mammals, wintering raptors, and songbirds, in large part due to regional connectivity.
Retain connectivity and linkage values between major canyons of the SEA, and especially at choke points and major road crossings.
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Table 1. Continued. Conservation Biology Institute 8 July 2005 Reference Target Species Major Focus Study Area Methods Relevant Results Recommendations Lyren 2001 Coyotes and bobcats
Home range and movement characteristics, roadkill, and underpass use by bobcats and coyotes.
Primarily along SR 71 and adjoining areas occupied
by telemetered
animals.
Radio telemetry (29 coyotes, 4 bobcats); roadkill surveys along SR-71.
Home ranges of about half of all telemetered animals overlapped SR71, indicating frequent road crossing by individuals. Most animals crossing
the road were documented using underpasses; coyotes used underpasses more than bobcats. Coyote use of underpasses seemed suppressed by traffic volume. No bobcats were found road-killed; coyotes frequently were road-killed, with concentrations where no wildlife fencing was present along road.
Wildlife fencing should be used to funnel wildlife to underpasses.
Schlotterbeck 2001
Large and mediumbodied mammals; reptiles and amphibians.
Assemble existing data from Haas and Crooks 1999 and Case and Fisher 1998 into a GIS database.
Entire PuenteChino Hills Wildlife Corridor, from Santa Ana River to Whittier Hills.
No original field studies. Interviews with previous researchers and compilation and analysis of existing field data.
See entries for Haas and Crooks (1999) and Case and Fisher (1998) below. A comprehensive GIS database of their results was made available for research and monitoring.
Conservation and restoration of numerous lands, and proper management of these lands, is essential to stave off further species losses and ecological collapse in the Puente and Chino Hills.
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Table 1. Continued. Conservation Biology Institute 9 July 2005 Reference Target Species Major Focus Study Area Methods Relevant Results Recommendations Haas et al. 2002, Case and Fisher 1998 Reptiles and amphibians
Determine distribution and diversity of herpetofauna; identify management needs to maintain diversity.
Scattered locales across the PuenteChino Hills Wildlife Corridor, from Chino Hills State Park to Whittier Hills.
Field methods:Pitfall drift-fence arrays and snake traps. Statistical analyses: Several measures of species richness and diversity analyzed relative to landscape position.
Species richness and diversity were generally highest in the Chino Hills (22 species) and Whittier Hills (14 species), with lower levels in the narrower, more fragmented areas between (10-12 species). The number of sensitive species declined from seven in the Chino Hills to four in the Whittier Hills, and the western limit for some species lies somewhere between Chino Hills and Whittier Hills. Several species (e.g., coast horned lizard, western skink, red diamond rattlesnake) showed decreased population densities moving west through the corridor.
Maintain habitat linkages to maintain gene flow and reestablishment of populations if localized extinctions occur.
PCR 2002 General
wildlife, with focus on large mammals.
Assess onsite biological resources and wildlife movement corridors to understand constraints to development on the ShellAera property.
Shell-Aera property and immediate vicinity; representing the western half of the Missing Middle (between SR-57 and Harbor Blvd.).
Sign reconnaissance; unbaited track stations, camera stations, and scat surveys focused on expected corridors and bottlenecks, such as road crossings; analysis of roadkill records.
Documented use of Shell-Aera property by deer, bobcat, coyote, roadrunners, and other native wildlife. Greatest evidence of wildlife movement was concentrated from the southeast corner of the property (associated with Tonner Bridge) to the northwest corner (associated with Drainage 26 and an area of high roadkill on Harbor Blvd.). Documented primary and secondary movement corridors across the property.
N/A--This biological constraints analysis describes existing conditions on the property and does not present recommendations.
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Methods
This study synthesized and updated existing information on wildlife distribution and movements in the Puente-Chino Hills Wildlife Corridor (see Table 1) to serve as a “meta-analysis” of overall corridor function and of the role that each portion of the corridor plays in supporting native wildlife and wildlife movement. After analyzing existing conditions, I also considered how land-use changes in the Missing Middle could affect the continued persistence of wildlife populations throughout the corridor and in each portion of the corridor. The analytical process involved
1. Selecting a suite of target species for which there is sufficient local information to assess distribution and movements;
2. Defining geographic units of the corridor system and assessing their functions in supporting these target species;
3. Assessing the roads that segment the study area as potential barriers or filters to movement; and
4. Assessing how the current functionality of these segments could change with various development scenarios.
Reconnaissance
The analysis of existing literature was supplemented with reconnaissance surveys in the field as well as using satellite imagery, high-resolution aerial photographs, and digital photographs taken during flyovers by Melanie Schlotterbeck. In particular I used the Keyhole program (www.keyhole.com) to perform a “virtual reconnaissance” of the study area, including properties where physical access was not possible. Keyhole3
allows a user to zoom, pan, tilt, rotate, and
otherwise explore a three-dimensional digital model of the Earth’s surface covered with high resolution satellite imagery (2004-5 color images at 1-m resolution) and Geographic Information System (GIS) data that can be layered onto this imagery. This proved to be an ideal tool for “exploring” the terrain prior to the field visit, and while reviewing previous studies in the area, to determine how topography, vegetation, development, and other landscape features might influence target species movements. By zooming in, rotating, tilting, and moving along this virtual landscape, a wildlife biologist can readily see where steep terrain, road cuts, bridges, vegetation, housing developments, and other landscape features would tend to funnel movements by larger species across the study area. (For example, I predicted, based on Keyhole reconnaissance, that the stretch of Harbor Boulevard just south of Wellington Lane would be a deadly road crossing for large mammals, which was later confirmed by personal observations in the field and my literature review.)
3 Reduced-resolution screen captures of Keyhole imagery are used to illustrate landscape issues throughout this report.
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After extensive exploration of the study area using Keyhole, GIS, and high-resolution aerial imagery, I visited the study area on March 2, 2005. I drove all roads crossing the area, stopping to investigate road-crossing structures (bridges, culverts, etc.), walking sections of trails, and looking for wildlife and wildlife sign. I photographed key locations, roadkills, habitat conditions, and other pertinent scenes, and noted signs of wildlife on aerial photographs.
Because my fairly cursory field observations strongly reinforced the quantitative results of more intensive studies (see Table 1), they are not presented in detail, but are cited as supporting or supplemental evidence for the results and recommendations of these previous studies.
Target Species
It is important to clearly define what species and ecological processes are expected to benefit from a wildlife movement corridor (Rosenberg et al. 1997, Beier et al. in press). Target species were selected based on data availability (see Table 1) and how well they reflect overall corridor function or serve as indicators of habitat fragmentation and movement constraints. They include species that require large areas to survive, are most susceptible to extirpation by habitat fragmentation, are most susceptible to roadkill, or for which roads may serve as physical barriers. In addition, previous studies provide some more general measures of ecosystem health and corridor function, such as species richness for amphibians and reptiles (Haas et al. 2002) and avifauna (Cooper 2000).
Although it is tempting to think of one or a few larger mammal species as most obviously served by movement corridors, the ecological effects are far broader than any single species or set of species. Ultimately, the objective of securing and managing the Puente-Chino Hills Wildlife Corridor is more than ensuring that mountain lions can continue roaming the area (although that is certainly one objective)—it is ensuring that healthy ecological communities can continue to thrive and support the broadest possible range of native species.
Mountain Lion
The mountain lion or puma (Puma concolor) is the top carnivore in Southern California. It is a true “keystone” species whose presence helps maintain ecological balance by controlling populations of deer and other prey (Soulé and Terborgh 1999, Crooks and Soulé 1999).
Mountain lions require huge contiguous habitat blocks to persist, with individual lions roaming home ranges as large or larger than the entire Puente-Chino Hills study area. Only contiguous habitat areas large enough to support at least 20 individuals—about 2,000 sq. km in Southern California—are expected to support lion populations over even the short term (Beier 1993, Beier et al. in press). Due to demographic instability and inbreeding concerns, even populations meeting these criteria, such as the population of about 20 adult lions occupying the 2,070-sq.-km Santa Ana Mountains Range, must be connected to even larger populations for long-term persistence (Beier 1993).
Although the Puente-Chino Hills are too small (at about 163 sq. km) to support a population of mountain lions on their own, one to several lions live totally or partially within the hills as an Puente-Chino “Missing Middle” Analysis
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extension of the larger Santa Ana Mountains population (Beier 1993, Noss et al. 1997). The Coal Canyon wildlife underpass on Highway 91 was restored specifically to ensure the continued presence of these large predators in the Puente and Chino Hills, thus ensuring a more healthy and balanced ecosystem (Noss et al. 1997). Lions have been detected all the way to the westernmost portions of the corridor (Whittier Hills) in recent years (A. Henderson, A. Gullo, and C.
Schlotterbeck, personal communications).
Lions are very prone to roadkill. During Beier’s (1993, 1995) study of mountain lions in the Santa Ana Mountains, vehicles killed 33% of the population, including four lions killed at one road-crossing during a 2-year period. Thus, mountain lions are good focal species for conservation planning in the study area, due to their keystone status, large area requirements, dependence on intact corridors, and susceptibility to roadkill.
Bobcat
Bobcats (Lynx rufus) are excellent indicators of functional landscape connections at the scale of interest in the Puente-Chino Hills study area (Crooks 2002, Haas 2002, Tigas et al. 2002, Riley et al. 2003). In Southern California, bobcat home ranges average about 2 to 6 sq. km, and population densities average about 1.1 to 1.6 bobcats per sq. km (Riley et al. 2003, Lembeck 1978, Lyren 2001). The probability of bobcat occurrence in a habitat patch is directly related to both the size of the patch and its isolation from other patches (Crooks 2002), with patches as small as 10 sq. km highly likely to support a few individuals if they are close enough together (within 1 km or less) and adequately connected to allow inter-patch movement (Crooks 2002).
Using radio telemetry in the Santa Monica Mountains, Riley et al. (2003) found habitat blocks as small as 3.15 sq. km to support a few individuals, as long as movement was possible to larger, source population areas. Taking into account variation in habitat quality, Beier et al. (in press) concluded that contiguous habitat blocks of about 60 sq. km are necessary to support potential source populations of 20-25 adult bobcats over the short term in Southern California. Noss et al. (1997) estimated that a population of less than 50 bobcats inhabited the Puente and Chino Hills and less than 500 bobcats inhabited the Santa Ana Mountains. Haas (2002) found bobcats to be associated with wider portions of the Puente-Chino Hills, with lower densities in narrower segments. He concluded that bobcats used smaller segments primarily as “move-through” rather than “live-in” habitat.
Bobcats are behaviorally secretive and tend to avoid roads and other human disturbances, although they remain quite susceptible to roadkill. Bobcats are less likely to use road underpasses than coyotes, especially narrow underpasses or underpasses near residential areas, and so may be better indicators of high-quality road-crossing structures for wildlife.
Coyote
Coyotes (Canis latrans) are more adaptable, more abundant, and less averse to fragmentation than bobcats and mountain lions—and thus less dependent on high-quality landscape connections. Nevertheless, coyotes are important to maintaining ecological balance (Crooks and Puente-Chino “Missing Middle” Analysis
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Soulé 1999) and are good indicators of problem road-crossings, as many are killed on roads in the study area and elsewhere (Lyren 2001, Haas 2000, Robertson et al. 1995). Concentrations of coyote roadkills provide good indicators of potential crossing locations for other species, including bobcats, mountain lions, and mule deer. Noss et al. (1997) estimated a carrying capacity of roughly 60 adult coyotes for the Puente and Chino Hills and less than 500 in the Santa Ana Mountains.
Mule Deer
Mule deer (Odocoileus hemionus) are the primary prey of mountain lions and require relatively large habitat areas to support populations. Although they adapt to living in close proximity to humans, and are found in portions of the study area that are effected by fragmentation and development edges (Haas 2000), they are prone to roadkill and highly selective of road-crossing structures. In general, deer will use only the largest, most open types of structures (bridges or very open box culverts) within well-vegetated habitat areas to cross under (or over) roads (Haas 2000, Clevenger and Waltho 1999, Evink 2002). Noss et al. (1997) estimated that about 400 mule deer may inhabit the Puente and Chino Hills and about 4,000 may inhabit the Santa Ana Mountains.
Greater Roadrunner
Greater roadrunners (Geococcyx californianus) are associated with coastal scrub and open brush mosaics in coastal Southern California. They are highly susceptible to roadkill (Unitt 2004) and particularly sensitive to habitat fragmentation, rapidly disappearing from isolated habitat patches (Unitt 2004, Crooks et al. 2001, Soulé et al. 1988, Garrett and Dunn 1981). Soulé et al. (1988) and Crooks et al. (2001) identified the roadrunner as the most sensitive to habitat fragmentation of eight scrub-dwelling species they addressed in San Diego County. Crooks et al. (2001) found roadrunners persisting in only one of 34 canyons isolated by urbanization, and estimated that the roadrunner has a good chance of persisting only in patches 1.6 sq. km or larger. Based on more exhaustive surveys, Unitt (2004) concluded that this underestimates roadrunner sensitivity to isolation; he suggested that even 4.0-sq. km patches may be too small to sustain populations for long. As snakes and lizards are important prey, roadrunners may decline with reductions in reptile diversity and abundance.
Cooper (2000) reported that roadrunners are scattered in association with scrub habitats throughout the Puente-Chino Hills study area, with particular concentrations in the hills north of Brea and Yorba Linda (including significant portions of the Missing Middle). He estimated there were more than 50 breeding pairs (100 adult individuals) living in the Puente and Chino Hills.
Coast Horned Lizard
The coast horned lizard (Phrynosoma coronatum) was once common and widely distributed in coastal sage and chaparral habitats of Southern California, but has been extirpated from much of Puente-Chino “Missing Middle” Analysis
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its former range by habitat loss and fragmentation (Fisher et al. 2002). This species is highly impacted by edge effects, such as invasions by the nonnative Argentine ant, which eliminates the native harvester ants that comprise more than 95% of the horned lizard’s diet (Suarez et al. 2000). Argentine ants are closely associated with human-altered (especially irrigated) landscapes in Southern California, but can invade hundreds of meters into native scrub habitats; their adverse effects on native invertebrate populations ripple through the ecological community with devastating effects on biological diversity (Suarez et al. 1998). Thus, horned lizards serve as good indicators of relatively intact ecological webs and processes or, conversely, of the adverse effects of habitat fragmentation and edge effects on ecological communities (Fisher et al. 2002). They are also highly susceptible to roadkill and trampling. Case and Fisher (1998) and Haas et al. (2002) found coast horned lizards in the Chino Hills, as far west as the ridges between Carbon Canyon and Tonner Canyon (near the Olinda Landfill), but did not detect them at points farther west. Therefore, this species may already be extirpated, or likely will be soon, in corridor segments west of Highway 57 due to isolation of populations by roads and high mortality in remaining habitat areas.
Other Target Resources
The above target species certainly do not comprise a complete list of resources subject to loss due to habitat fragmentation and associated effects. They serve as indicators for a much more diverse community of organisms, and were chosen largely on this basis as well as the availability of distribution data in the study area. In addition to these species, I examined information on the diversity and abundance of reptiles and amphibians (from Case and Fisher 1998, Haas et al. 2002) and birds (Cooper 2000), and considered, at least qualitatively, the effects of habitat fragmentation on other species and ecological processes in the study area.
Defining Geographic Units, Barriers, and Filters
Although the entire study area serves as a wildlife movement corridor at a gross scale, it functions more like a peninsula of somewhat discrete habitat blocks segmented by roads and other discontinuities (Haas 2000, Haas and Crooks 1999, Schlotterbeck 2001, Robertson et al. 1995). The Puente-Chino Hills Wildlife Corridor was therefore subdivided into discrete geographic units based on habitat contiguity and intervening roads. Each unit, including the Santa Ana Mountains (the core area from which the corridor system projects) and the isolated terminal segment at the Whittier Narrows (Robertson et al. 1995), was given a geographic name to facilitate comparison (Map 2). Following Haas and Crooks (1999), the seven units between these two extremes (or between Highway 91 and Interstate 605) were also numbered 1 to 7, from east to west. These seven segments comprise the functional Puente-Chino Hills Wildlife Corridor system. They are convenient for comparing results across the various field studies and for assessing how each segment, and the habitat breaks between them, contribute to overall functionality of the corridor system. These segments are therefore useful tools for conservation planning.
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Map 2. Geographic units of the Puente-Chino Hills Wildlife Corridor.
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Initial Classification of Geographic Units
Each geographic unit was first classified by the primary role it appears to play in the overall functioning of the wildlife corridor system—as a biological core, subcore, patch, or isolate.
These functional categories, defined below, reflect the relative size and contiguity of the units and their ability to sustain populations or facilitate movements of target species, as supported by literature and results of previous wildlife studies here. These definitions are tailored to this particular study, based on well established conventions in reserve design (e.g., Noss 1987, Meffe and Carroll 1997, Soulé and Terborgh 1999), and modified slightly from concepts and definitions developed for the South Coast Missing Linkages project—a science-driven approach to conserving landscape connectivity throughout the South Coast ecosystem (Beier et al. in press). The most significant deviation from the definitions of Beier et al. (in press) is the inclusion of an intermediate-sized “subcore” class (which corresponds to a “patch” in Beier et al. in press).4
• Core — A core area must be large enough (> 2,000 sq. km) to sustain populations of most or all target species without the need for frequent immigration from other areas, and should have relatively high biological diversity and a low proportion of edge. Core areas support source populations of target species, which may contribute individuals to other, less substantial, blocks of habitat. Basically, a core should be large enough to support a population (at least over the short term) of the most wide-ranging and area-dependent target species, which in this case is the mountain lion. • Subcore — Subcores are contiguous blocks of habitat at least 60 sq. km, but less than 2,000 sq. km (corresponding to a “patch” as defined by Beier et al. in press). Subcores are too small to sustain a population of mountain lions in isolation, but large enough to support a population of bobcats with at least occasional dispersal. Subcores may support one or a few individual mountain lions, or at least provide significant “live-in” habitat as part of one or more lion home ranges. Subcores are more edge-effected than cores and may sustain lower overall species diversity, but can nevertheless represent significant source populations for numerous other target species, such as roadrunners, coyotes, and horned lizards.
• Patch — Patches, at less than 60 sq. km, are smaller and more edge-effected than subcores and are expected to support overall lower numbers and diversity of species. In isolation, patches may be too small to support a population of bobcats, and perhaps other target species having intermediate area requirements, although they could support a small number of such species or at least represent live-in or move-through habitat for individuals of such species. Although they may support populations of less area-
4 Concepts like “core” and “corridor” are species- and scale-dependent, such that what might be considered a movement corridor for one species (e.g., mountain lion) can be core “live-in” habitat for other species (e.g., lizards, songbirds, or rodents). This entire study area is widely recognized as a “wildlife corridor,” even though numerous on-the-ground travel routes, population concentrations, etc., can exist within this overall corridor system at finer resolution.
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dependent target species, patches may serve mainly as dispersal stepping stones (or “move-through” habitat) for individuals of larger species (like mountain lions) moving between larger geographic units.
• Isolate — An isolate is any patch that is separated from another geographic unit by barriers to movement for target species. For example, the Whittier Narrows are separated from the Whittier Hills by Interstate 605, other significant roads, and commercial development, and are considered functionally isolated from the corridor for nearly all reptiles, amphibians, and mammals (Haas and Crooks 1999, Haas et al. 2000, Robertson et al. 1995, personal observations).
Note that these initial landscape categories were defined based primarily on the needs of the most area-dependent target species (mountain lion and bobcat). However, such concepts as “core” and “patch” can also be defined separately for each target species, based on their own requirements. Thus, a patch of habitat too small to support mountain lions could represent a “core” population area for less area-dependent species, like the roadrunner or horned lizard.
Such species-specific issues were treated in more detail in later analytical steps.
Classifying Barriers and Filters to Movement
Roads and other discontinuities in habitat were also classified based on their relative effects on movements and population distributions of species, as follows:
• Barriers and Near Barriers — Roads or other discontinuities between geographic units that are never (for barriers) or rarely (for near barriers) crossed by target species. Barriers effectively isolate target species populations on adjacent habitat units from one another, while near barriers may separate subpopulations into a “metapopulation” system, with individuals occasionally dispersing between subpopulations in different units. For wideranging species like bobcats or mountain lions, barriers or near barriers may define one boundary of a home range, as individuals recognize it as the edge of available habitat.
Major freeways and associated physical features (e.g., embankments, drainage improvements, retaining walls, lane dividers, fences, wide areas devoid of vegetation) create impassible barriers for nearly all ground-dwelling species, unless sufficient crossing structures (e.g., bridges, culverts, vegetated over-crossings) facilitate movements (Beier et al. in press, Evink 2002, Haas 2002, Lyren 2001). For example, the concentration of roads and commercial developments associated with Interstate 605, separating Whittier Hills from Whittier Narrows, represents a barrier for most or all target species. Near barriers are similar, but they may have one or more crossing structures that can be used by at least some target species; or target species may occasionally cross atgrade, on the road surface (perhaps at high risk of roadkill). Highway 57 and Harbor Boulevard are examples of near barriers in the study area. Both have high traffic volumes and physical characteristics that discourage crossings, except at one excellent bridge crossing at Tonner Canyon (for Highway 57) and one stretch where wildlife cross Harbor Boulevard at-grade—albeit with frequent roadkill.
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• Filter (Permeable and Highly Permeable) — Filters are discontinuities in habitat connectivity that are readily to moderately crossable by most but not all target species.
For example, two-lane paved roads with low traffic volumes and little associated development are readily crossed by larger mammals (although there may be occasional roadkill); but other species, like horned lizards, may be reluctant to cross or may suffer high roadkill. Thus, such roads serve to “filter” some species out of the community of wildlife crossing between adjoining habitat units. Several permeable to highly permeable roads cross the study area, such as Turnbull Canyon Road through the Whittier Hills (between Segments 6 and 7). The larger mammals, roadrunners, and some reptiles probably cross this road at-grade with little hesitation, and individual home ranges may straddle it. However, some smaller or more sedentary species may have their populations segmented by this road into subpopulations, with only occasional cross-road dispersal.
Analyses — Assessing Existing and Future Functionality
For each target species, I followed the following analytical steps:
1. I assigned each of the nine geographic segments to one of the functional categories (core, subcore, patch) as if each functioned independently of the others (i.e., as if roads separating the units acted as barriers or near barriers to dispersal). This initial categorization was based exclusively on unit size. For example, any unit less than 60 sq. km would be considered a patch if it functioned independently of other units in supporting a target species.
2. I assessed each road separating the units to determine whether it acted as a barrier (or near barrier) or filter (permeable to highly permeable). If a road was not considered a barrier/near barrier for a target species, and the two units it separated appeared to function as one larger unit for that species, the area of the two units was summed and the function of the new composite unit was reassessed. For example, if the composite unit exceeded 60 sq. km, it was considered to function as a subcore rather than two separate patches.
3. Based on this revised, species-specific functionality assessment, I assigned each newly defined unit (or composite unit) a function relative to supporting individuals or populations of each target species based on unit size, habitat composition, and other factors gleaned from the literature and field reconnaissance. These species-specific functions were defined as follows:
• Population — capable of supporting a breeding population of at least 20 adults and potentially serving as a source of individuals that disperse into other units. • Subpopulation — capable of supporting at least two but less than 20 breeding individuals. Not likely to be a reliable source population, but may exchange individuals with other areas within a larger metapopulation (a set of partially isolated Puente-Chino “Missing Middle” Analysis
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populations linked by occasional dispersal) and may provide individuals to recolonize habitat patches in case of local extirpation.
• Home Range Part — incapable of supporting at least two breeding individuals on its own, but may provide live-in habitat (e.g., foraging or resting cover) and form a part of one or more individuals’ home range(s).
• Move-through — not contributing significant live-in habitat for a species as part of a functional home range, but capable of accommodating movements between more substantial units within a home range, or potentially used for dispersal between other habitat units.
4. This classification system was used to assess likely effects of future scenarios on wildlife populations or movements, such as (a) adding new roads or development that would introduce new barriers or reduce the size of a functional unit, or (b) adding or improving wildlife crossing structures that would allow two independent units to serve as one larger one.
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Results
Functionality of Geographic Units
Table 2 summarizes characteristics of the geographic units, including their size, vegetation composition, known or inferred presence/absence of target species, initial functional classification (core, subcore, patch), and reserve status (conserved/unconserved). Only the Santa Ana Mountains unit met the definition of a core area (larger than 2,000 sq. km and capable of supporting a mountain lion population). The Chino Hills between Highways 91 and 142 met the definition of a subcore (60-2,000 sq. km and capable of supporting a population of bobcats). Six other segments of the Puente-Chino Hills Wildlife Corridor met the definition of patch, but with great variation in their capacity to support wildlife and wildlife movements. The disjunct Whittier Narrows met the definition of an isolate.
Table 3 summarizes pertinent characteristics of the major roads dividing these units, with a focus on their role as barriers or filters to wildlife movement. Following below is a more detailed, unit-by-unit review of the information, concerning how each unit appears to function in supporting wildlife populations and movements, considering the effects of intervening roads and other factors. This review starts with the Santa Ana Mountains Core Area, then describes the seven segments of the functional Puente-Chino Hills Wildlife Corridor, and ends with the isolated Whittier Narrows.
Santa Ana Mountains (Core)
At about 2,070 sq. km, wildlands in the Santa Ana Mountains comprise the only true core in the study area. They support a high diversity of wildlife in a relatively intact and healthy representation of Southern California’s South Coast ecosystem (Spencer et al. 2001), including substantial populations of all the target species. Noss et al. (1997) estimated populations of breeding adults in the Santa Ana Mountains at about 4,000 mule deer, 15-20 mountain lions, up to 500 bobcats, and more than 500 coyotes. These populations are large enough to persist, at least in the short term, within the Santa Anas without immigration from other habitat areas— although at least the mountain lion needs occasional immigration from adjacent mountain ranges to persist in the long term (Noss et al. 1997, Beier 1993). Of course, all species and ecosystem functions benefit from connectivity to other wildlands. The breeding population of about 15-20 mountain lions serves as a source of lions moving into the Puente-Chino Hills via the Coal Canyon Underpass (Beier 1995, Noss et al. 1997).
The Santa Ana core area is separated from the Chino Hills by busy Highway 91 and associated developments. However, the Coal Canyon Wildlife Underpass was restored specifically to mitigate this strong barrier to movements and appears to be functional (Figure 2).
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Segments of the Functional Puente-Chino Hills Wildlife Corridor Santa Ana
Mountains Chino
CarbonTonner Shell-Aera Powder- Schabarum San Miguel E. Whittier W. Whittier Whittier Narrows Segment Number N/A 1 2 3 4 5 6 7 N/A Size (sq. km.) ~2,070 85.6 44.3 13.3 5.7 1.5 5.2 7.1 ~4.5 Vegetation Mosaic Shrubland 51.3% 51.9% 45.2% 48.9% 57.1% 43.4% 67.0% Grassland 36.5% 29.4% 37.7% 21.0% 31.8% 36.1% 17.1% Woodland 12.1% 18.7% 17.2% 30.1% 11.4% 20.4% 15.9% Wetland N/A
0.1% 0.1% 0.0% 0.0% 0.0% 0.0% 0.0%
N/A
Spp. Presence/Absence* Mountain lion P P P P? P? P? P P A? Bobcat P P P P P P P P A? Coyote P P P P P P P P P? Mule deer P P P P P P P P ? Roadrunner P P P P P? P? P P ? Coast horned lizard P P P A? A? A? A? A? A? Biological Function core subcore large patch patch patch small patch patch patch isolate Reserve Status substantially conserved
substantially
conserved
Carbon Cyn
partly
conserved,
Tonner Cyn
unprotected &
threatened
unprotected
& threatened
partly
conserved,
partly
threatened
partly
conserved,
partly
threatened
substantially
conserved
substantially
conserved
substantially
conserved
*See Table 1 for supporting literature. P = confirmed present; A = likely absent; ? = presence or absence inferred by indirect evidence and geographic context, but no confirmatory data found.
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Conservation Biology Institute 22 July 2005 Table 3. Characteristics of roads crossing the Puente-Chino Hills Wildlife Corridor. Road Geographic Units Separated Critical Crossing Structures* Characteristics Effect on Movements SR 91 Santa Ana/Chino Coal Canyon Wildlife Underpass
Major, 6-lane freeway with heavy traffic and significant physical barriers to wildlife.
Barrier, except for Coal Canyon Underpass
Carbon Canyon Rd. (SR 142)
Chino/Carbon-Tonner Square box culvert near
Chino State Park entrance.
Busy 2-lane highway through mostly wild open space. Moderate-high coyote roadkill. Few physical barriers.
Permeable filter, with some roadkill (esp. coyote). Mix of at-grade crossings and culverts, at least one used by bobcat.
SR 57 Carbon-Tonner/ShellAera Tonner Canyon Bridge Major 6-lane freeway with heavy traffic and significant physical barriers to wildlife. Barrier except for Tonner Canyon Bridge, with documented use by deer, bobcat, and coyote.
Harbor Blvd. Shell-Aera/PowderSchabarum Harbor Blvd. Wildlife Tunnel (proposed) Major 4-lane arterial with heavy traffic and significant barriers to wildlife. High roadkill. Barrier, except for occasional at-grade crossing, with very high roadkill. Hacienda Blvd. Powder-Schabarum/San Miguel
none (except a littleused equestrian tunnel that could be improved) Busy 2-lane road with steep slopes and cut banks, but several at-grade crossing areas.
Filter, with moderate roadkill risk.
Colima Rd. San Miguel/East Whittier Colima Service Tunnel Busy 4-lane road with physical barriers, including fences that may help funnel wildlife to undercrossing.
Filter, with relatively low roadkill due to fences and a well-used undercrossing with known use by deer, bobcat, and coyote.
Turnbull Canyon Rd.
East Whittier/West Whittier
none Winding, 2-lane road with light traffic
through wild habitat.
Highly permeable filter, with at-grade crossings in wild open space.
Interstate 15 & Workman Rd.
West Whittier/Whittier Narrows
none Major 6-lane freeway with heavy traffic, plus
other major and minor roads, commercial development, and other physical barriers to wildlife.
Barrier to essentially all ground-dwelling species.
*Includes only those structures used by diverse target species and especially larger mammals. Numerous smaller culverts that may serve some target species also occur, as do some larger equestrian tunnels that are in landscape positions not favoring use by target species. See Haas (2000) and Robertson et al. (1995) for a more comprehensive review of crossing structures in the study area.
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undoubtedly reflect the larger size of Segment 1 (and adjoining Segment 2) compared with other segments, its proximity to the Santa Ana Mountains Core, and the increasing number of barriers and filters encountered moving west from this source area through the corridor. Similar patterns in diversity, abundance, and evenness measures would be expected for other taxa (e.g., birds, small mammals, insects, plants) if comparable data were available to document them.
Segment 1 is largely conserved already as Chino Hills State Park, although efforts continue to increase the size and buffering of this important reserve area. It is separated from Segment 2 by Carbon Canyon Road (Highway 142). This busy 2-lane road suffers some roadkill, especially coyote (Robertson et al. 1995), but is generally quite permeable to target species due to extensive, naturally vegetated land on both sides, lack of development over much of its length, and availability of several undercrossings. The most significant undercrossing is a 1.4-m (4.5-ft) high square box culvert used by bobcats and other target species (Robertson et al. 1995). This road is therefore classed as a permeable filter, allowing Segments 1 and 2 to function as one larger subcore for most species and ecological processes. Notably, Haas et al. (2002) and Case and Fisher (1998) recorded coast horned lizards on both sides of Carbon Canyon Road, but not farther west along the corridor.5
Corridor Segment 2—Carbon-Tonner
This large (44.3 sq. km) patch appears to function more as an extension of the Chino Hills subcore, being separated only by permeable Carbon Canyon Road (see previous). It is biologically diverse and supports all target species, including the westernmost observations of horned lizards by Haas et al. (2002) and Case and Fisher (1998). The southern portion of Segment 2 (including lower Carbon and Tonner Canyons and associated ridges) has been identified as a conservation priority for birds due to its support of several regionally rare or declining species, including greater roadrunners, loggerhead shrike, cactus wren, California gnatcatcher, grasshopper sparrow, and sage sparrow, among others (Cooper 2000). The northern portion of the segment (upper Tonner Canyon) is also rated as a conservation priority for birds, including golden eagle, burrowing owl, northern harrier, cactus wren, tricolored blackbird, and grasshopper sparrow, among others (Cooper 2000). Tonner Canyon also supports significant California walnut woodlands.
The eastern half of Segment 2 contains the western slopes and ridges of the Carbon Canyon landscape and is partially conserved as part of Chino Hills State Park and the Firestone Scout Reservation. The western half of this segment, containing most of Tonner Canyon, is unconserved and threatened by several proposed developments. Tonner Canyon is almost entirely owned by the City of Industry, which proposes a new road along the east side of Tonner Canyon (Map 2) and new water reservoirs within the canyon. This threatened half of the segment comprises the eastern portion of the Missing Middle.
5 During my literature review, I found no recent confirmed records for coast horned lizards farther west than a ridge between Carbon and Tonner Canyons near Olinda Landfill (Haas et al. 2002). However, one table in a draft report (LSA 2005) listed the species as “observed” in the Whittier Hills, although another table in the same reference indicated the horned lizard as potentially present but not observed there.
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used crossing structures. An existing equestrian tunnel, that is infrequently used by target species, could be improved with fencing and revegetation (Haas 2000 and personal observations). Hacienda Boulevard has several at-grade crossing concentrations and trails (Haas 2000, Robertson et al. 1995, personal observations), which are probably associated with moderate roadkill. I rated this as a permeable filter, as it is crossable by most target species; however, it may act as a strong filter due to these and other constraints, and it represents a bottleneck to movement in need of improvement (Haas 2000).
Corridor Segment 5—San Miguel
This is the smallest (1.5 sq. km) segment of the entire corridor system. Along with the narrow constriction in the west end of Segment 4, this segment represents the narrowest habitat constriction along the wildlife corridor system (0.5 to 1.0 km wide). It is also perhaps the most disturbed by humans and their pets, particularly on northern slopes (Haas 2000, Robertson et al. 1995). Haas recorded low use by target species (no bobcat use) on the northern portions of this segment, along the Skyline Trail, but high levels of cats, dogs, striped skunks, and raccoons. The abundance of these mesopredators that are adapted to human environments often reflects low presence of coyotes and other large predators, which suppress these species when present (Crooks and Soulé 1999), as well as higher human influences and edge effects. Haas (2000) recorded bobcat activity in the southern portion of the segment, in association with less disturbed areas of San Miguel Canyon and near Skyline Drive. He noted that the transects with the greatest bobcat activity were also those with the lowest dog activity. Haas surmised (as did Robertson et al. 1995) that large mammals travel along Skyline Drive and descend into San Miguel Canyon towards the Colima Service Tunnel (discussed below). Low density housing in this segment, especially near Hacienda Boulevard, may reduce habitat quality for target species, but does not present barriers to movement (Haas 2000, Robertson et al. 1995). For some target species, Segment 5 may function primarily as move-through habitat, although a few coyotes and bobcats probably forage in San Miguel Canyon.
Segments 5 and 6 are divided by Colima Road, a fairly busy 4-lane road winding through a mix of open space and scattered housing. Although flanked by steep slopes, some fences, and other movement impediments, there are several at-grade crossing areas, which are associated with high coyote roadkill (Haas 2000, Robertson et al. 1995). One good under-crossing structure exists at a service tunnel near the southern edge of the habitat area (Colima Service Tunnel). Bobcats, coyotes, and deer use this tunnel (Robertson et al. 1995, Haas 2000, Haas and Turschak 2002), and they continued using it even after a dramatic increase in recreational uses of the tunnel and vicinity by humans and dogs during 2001-2002 (Haas and Turschak 2002). Most wildlife species use the tunnel between sunset and sunrise, whereas human and dog use occurs almost exclusively during daylight (Haas and Turschak 2002). Conserving and improving this tunnel for continued wildlife use, especially at night, is a conservation priority.
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Corridor Segments 6 and 7—East Whittier and West Whittier The wildlife corridor widens again in the Whittier Hills from the narrow and constrained Segments 4 and 5. Segments 6 and 7 are separated by Turnbull Canyon Road, which appears to be the most permeable road analyzed in the study area. It is a narrow, 2-lane road with relatively light traffic, winding through fairly undisturbed wildlands. Haas (2000) recorded no roadkills here and did not consider Turnbull Canyon Road a barrier or major hazard to mammals.
Likewise, Robertson et al. (1995) did not consider Turnbull Canyon Road a significant impediment to movement, which corresponds with my field observations. Consequently, Segments 6 and 7 are discussed here together as one continuous geographic unit (Whittier Hills).
The Whittier Hills support significant biological values despite their location at the terminus of the range of connected wildlands, far from the Santa Ana Mountains Core. This area had the highest levels of deer and bobcat activity recorded by Haas (2000), and higher species richness of reptiles and amphibians than narrower segments farther east (Haas et al. 2002). Mountain lion presence has recently been confirmed in the area by several lion-predated goats and deer, and at least one likely lion scat (Haas 2000; A. Henderson, C. Schlotterbeck, and A. Gullo, personal communications).
However, monitoring results also show that the Whittier Hills have lost some species and may be close to losing more due to their distance from core areas and numerous intervening barriers and filters to movement. For example, despite the relatively high total number of reptile and amphibian species they recorded here, Haas et al. (2002) also found the Whittier Hills to have the lowest overall evenness in the study area (Haas et al. 2002). This evenness finding means that the local herpetofauna consists of a few abundant species plus many less abundant species, in contrast to the Chino Hills, where high evenness indicated healthy populations of most species.
Those species detected in low numbers in the Whittier Hills may represent remnants of dwindling populations, possibly on their way to extirpation with little hope of being “rescued” by new colonists from other areas (Brown and Kodric-Brown 1977) due to the great distances and numerous barriers involved. Moreover, the Whittier Hills support fewer sensitive species of reptiles and amphibians than the Chino Hills, as various species drop out in an apparent east-west gradient from the Chino Hills through the wildlife corridor to the Whittier Hills (Case and Fisher 1998, Haas et al. 2002).
The Whittier Hills are separated from the Whittier Narrows by an array of formidable barriers, including Workman Road, Interstate 605, and a wide, unbroken surface of buildings and pavement. Together, these create a near total barrier to movement for all target species.
Whittier Narrows (Isolate)
Because it is functionally isolated from the Puente-Chino Hills Wildlife Corridor, I did not investigate this area in detail. Although this matrix of wetland and disturbed upland habitats probably supports some coyotes (a semi-isolated subpopulation?), it is unlikely to support other target species in perpetuity.
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Summary of Overall Corridor Function
In general, the Puente-Chino Hills Wildlife Corridor appears to be functional for at least larger mammals and birds, although tenuously so in the Missing Middle (due to several barrier roads and near barrier roads) and across smaller Segments 4 and 5 just west of the Missing Middle (due to their small size, strong edge effects, and high human and dog activity). Essentially all roads in the study area are considered barriers or at least strong filters to movements by many reptiles, amphibians, and small mammals, although most birds and larger mammals currently can move between all segments either at-grade (with mortality risks) or via critical crossing structures. Despite constraints in many locations along the corridor, target species are confirmed or highly likely to occur in all seven corridor segments, except for the coast horned lizard, which may already be absent, or will disappear in the future, west of Highway 57.
Mountain lions are capable of traversing the length of the corridor, albeit at some risk of roadkill, and one or more lions still hunt as far west as the Whittier Hills. Most other target species probably persist over the length of the corridor as metapopulations, with subpopulations segregated among geographic units by the presence of barrier or near barrier roads. These subpopulations may be linked demographically and genetically by occasional dispersal, or by within-home range movements of some individuals, depending on each species’ ability to navigate roads and crossing structures. For example, bobcats apparently have small subpopulations living in the Whittier Hills and within Segment 3 (Shell-Aera), and a larger source population living within the Chino Hills (Segments 1 and 2). Some individual bobcats probably have home ranges completely or partially within smaller segments (e.g., 4 and 5) between these more substantial habitat areas; or they occasionally move through the smaller segments, between larger ones, and thus keep the overall metapopulation interconnected demographically and genetically. This metapopulation persistence depends on both occasional cross-road movements (i.e., functional road-crossings) and sufficient patch size and habitat quality to sustain small subpopulations within segments.
Haas et al. (2002) described a gradient of declining diversity and evenness of reptile and amphibian species, moving west from the Chino Hills. This must be attributed to higher mortality and edge effects in the more fragmented portions of the study area, exacerbated by the greater distance and increasing number of barriers and filters that must be crossed as one moves farther west from source populations. This pattern of decreasing biological diversity in the western portions of the corridor is likely to be mirrored by other taxa that respond similarly to distance and barrier effects, such as small mammals. In terms of metapopulation dynamics, if a local population or subpopulation dwindles or disappears from one segment (e.g., Whittier Hills), it is less likely to be “rescued” by colonists from other segments (e.g., Chino Hills) the farther away it is from the source population and the greater the number of intervening barriers and filters. Hence, the farther west a segment lies, the greater the likelihood of local population declines or extirpations, at least for less mobile species (Haas et al. 2002).
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Table 4 summarizes the conclusions from the preceding review of geographic units and roads and presents a conceptual model of how each geographic unit (or composites of adjoining units lacking barriers) appears to function in supporting populations of target species within this segregated landscape. This table integrates diverse information, including published estimates of home ranges and densities of target species in Southern California, results of the monitoring studies summarized in Table 1, variation in habitat quality and mortality factors throughout the study area, and professional judgment. The carrying capacity estimates (in parentheses for some species) are rough approximations only, intended as order-of-magnitude estimates of the capacity of each geographic unit to support populations or subpopulations of target species, or to function as part of one or more home ranges, or to function as pass-through habitat between other units.
Where adjoining segments are considered to function as one unit for a particular target species (e.g., if individuals readily cross roads and populations are not considered segmented by them), the area of those segments is summed. Thus, Segments 1 and 2 are combined to form new Segment 1/2 (Chino-Tonner), because Carbon Canyon Road is quite permeable for most species.
Likewise, Segments 6 and 7 (the Whittier Hills) appear to serve as one contiguous geographic unit for nearly all target species, except the horned lizard, which is likely absent.
Vertical lines separating adjacent segments in Table 4 represent roads considered to segment populations for a given species. However, note that even where barrier roads do not prevent movement between adjoining segments, those segments may be treated separately in the table’s classification of segment function for a target species. For example, although the roads bounding Segment 5 are not considered mountain lion barriers, Segment 5 is rated separately as “passthrough habitat” for lions (due to small size and edge constraints), whereas Segment 4 and combined Segments 6/7 are considered foraging habitat and therefore parts of a functional home range for one or two lions that pass through Segment 5 to reach them. Similarly, although Colima Road is not a strong barrier to movement for bobcats, coyotes, or deer, narrow and edgeeffected Segments 4 and 5 likely support, at most, small subpopulations (a few resident individuals) or portions of a few individual home ranges for these species, whereas the larger and more contiguous Whittier Hills unit can support more robust and sustainable subpopulations.
By reading across the rows of Table 4 for any species, one can envision how the presence of species is maintained throughout the corridor via individual movements and metapopulation dynamics, with each segment (or combination of segments) serving as stepping stones along the way (either for an individual of a wide-ranging species like mountain lion—which may traverse the entire corridor—or over several generations for smaller species, whose individuals may move over only one or a few segments in a lifetime). For example, the only source population for mountain lions is the Santa Ana Mountains Core. The one to three resident lions that use the combined Chino-Tonner unit would not be there without this core population or the Coal Canyon Wildlife Underpass (Beier 1993, Noss et al. 1997, Haas 2000). One or more of these resident lions at least occasionally use Segment 3 (Shell-Aera) as foraging or pass-through habitat as a portion of their home range (made possible by the Tonner Bridge between Segments 2 and 3).
From there, one or more lions occasionally forage in or move through Powder Canyon (Segment 4) and San Miguel Canyon (Segment 5) to forage in the Whittier Hills (combined Segments 6/7).
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Segments of the Functional Puente-Chino Hills Wildlife Corridor 1/2–Chino-Tonner 6/7–Whittier Hills
Santa Ana Mtns
Core Area 1-Chino
2-CarbonTonner 3-Shell-Aera 4-Powder- Schabarum 5-San Miguel 6-E. Whittier 7-W. Whittier Whittier
Narrows
(Isolate)
Unit Size (sq. km) 85.6 44.3 5.7 1.5 5.2 7.1 Summed Size ~2,070
129.9 13.3 7.2 12.3
~4.5
Target Species Mountain lion Pop (15-20) Subpop (1-3) HR Part (1-2) HR Part (1-2) Pass-thru HR Part (1-2) Absent Bobcat Pop (100-400) Pop (20-50) Subpop (2-10) Subpop/HR Part (2-5) Subpop (5-15) Absent? Coyote Pop (200-500) Pop (20-50) Subpop (5-12) Subpop/HR Part (2-7) Subpop (15-25) Subpop? Mule deer Pop (2,000-4,000) Pop (100-300) Subpop (10-25?) Subpop/HR Part (5-15) Subpop (15-30) Absent? Roadrunner Pop (hundreds) Pop (20-100) Subpop (?) Subpop (?) HR Part (?) Pop(?) Absent? Coast horned lizard Pop (thousands) Pop (hundreds?) Pop (hundreds?) Absent? Absent? Absent? Absent? Absent? Absent? Pop = capable of supporting a breeding population of >20 individuals and potentially serving as a source population via dispersal to other segments.
Subpop = capable of supporting 2-19 individuals as part of a metapopulation connected by at least occasional dispersal between other segments.
HR Part = could comprise part of one or more individual home ranges in concert with adjoining areas, but by itself is unlikely to support a breeding pair. Pass-thru = used for movement between adjoining units, but unlikely to support individual life requisites (foraging, breeding, etc.) or a home range.
SR 57
Harbor Blvd
Colima Rd
SR 91
I- 605
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If any of the critical road crossings becomes non-functional, lions would no longer use more westerly segments, because no segments are capable of supporting a population of lions in isolation (other than the Santa Ana Mountains Core). Moreover, if any segment is reduced in size or quality to become only move-through habitat (rather than live-in habitat), the probability of lions using this unit, or any units lying further west, would drop considerably. Hence, maintaining lions in the Whittier Hills ecosystem depends not only on maintaining the possibility of unimpeded movement by individuals along the corridor, but also on maintaining substantial live-in habitat along the way.
Similarly, subpopulations in the Whittier Hills of bobcats, mule deer, roadrunners, and, to a lesser extent, coyotes exist in part due to other population or subpopulation segments (i.e., source habitats) along the corridor. Thus, the substantial habitat blocks in Segments 2 and 3 are important to continued presence of target species many kilometers away in the Whittier Hills.
Substantial reduction in the carrying capacity of any one segment increases the probability of species losses in other segments. Thus, for example, the large area of Segment 3 (Shell-Aera) is a major potential contributor to the continued presence of bobcats, mule deer, mountain lions, roadrunners, and many other species in the Whittier Hills, especially if habitat quality is increased and road crossings are improved.
To summarize, the ability of westerly segments of the corridor to support species depends both on (1) the potential for individual movement between each set of adjoining segments (a function of roads and road crossings), and (2) having sufficient live-in habitat along the way to support populations or subpopulations that contribute dispersing individuals. The greater the distance from or between source populations, the lower the probability of a habitat patch or group of patches to continue supporting that species. If the distance between occupied segments becomes too great, or if barriers prevent inter-segment movement, local extinctions are inevitable in the isolated segments. Thus, any reduction in the capacity of segments to support populations or subpopulations increases the probability of local extinctions in that segment, as well as in all other “downstream” segments to the west.
Importance of the Missing Middle to Corridor Function
This understanding of overall corridor function highlights the importance of the Missing Middle as a part of larger home ranges for more area-dependent species and for maintaining species use of segments farther west. Although there has been much attention to maintaining or improving road-crossing structures and avoiding new impediments to movement, there should be equal attention to maintaining functional habitat blocks, capable of supporting source populations of target species, within the Missing Middle. Currently, the eastern half of the Missing Middle (Tonner Canyon) serves as an extension of the large Chino-Tonner subcore, contributing dispersing individuals of target species to other segments. Likewise, Segment 3 (Shell-Aera), although somewhat smaller and degraded by grazing, undoubtedly supports significant numbers of target species that disperse (at some risk) across Harbor Boulevard into Powder Canyon and beyond.
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Although this conceptual plan appears to show approximately half the property as open space, it is clear that this open space represents far less than 50% of the property’s biological value, due to severe fragmentation and edge effects, disruption of movements, and elimination of live-in habitat. Much of the open space would be totally isolated between bubbles of development and roads, such as the open space bubble on the west side of Highway 57. This and other open space patches would be completely isolated from other habitat areas, removing their capacity to support target species and other native wildlife. Moreover, the narrow and highly convoluted bits of open space depicted in this plan would suffer severe edge effects, greatly reducing the area’s ability to support wildlife and ecological processes. As just one example, Argentine ants routinely invade several hundred meters from suburban edges into native scrub habitats, and even farther in moist drainages and canyons (Suarez et al. 1998). The open space bubbles are all less then 1 km across—much less in many places. Consequently, most if not all of the open space depicted in Figure 5 will be invaded by Argentine ants, which eliminate numerous native arthropods, plants, and vertebrates (such as the horned lizard) in a process of ecological collapse already well-documented in Southern California ecosystems (Suarez et al. 1998). In conclusion, only a minor fraction of remaining habitat will remain biologically useful in this proposed development area, and even that would be highly degraded relative to existing conditions.
The conceptual plan appears to be sensitive to wildlife movement needs in its depiction of a continuous “Wildlife Corridor” across the property, from Tonner Bridge through Drainage 26, to the location of the new wildlife tunnel being constructed under Harbor Boulevard. However, this characterization, apparently based on the primary movement corridor across the property as mapped by PCR (2002), is simplistic and biologically misleading. As concluded in the above review of corridor functions, long, narrow gauntlets of “move-through” habitat will not ensure continued functionality of the corridor system, which depends heavily on retaining the large blocks of live-in habitat in the Missing Middle. The mapped open-space corridor is about 4.5 km long and averages less than 500 m wide, which is insufficient to provide reliable live-in habitat for mountain lions and bobcats, for example. This is especially true considering that Segments 4 and 5 are also rather narrow and edge-effected, with marginal capacity to support foraging mountain lions or a subpopulation of bobcats. The overall result would be about 13 km of mostly linear, edge-effected, move-through habitat for these species, from live-in habitat east of Highway 57 to the next reliable foraging or subpopulation area in the Whittier Hills. The likelihood of continued movements by at least bobcats and mountain lions between Tonner Canyon and Whittier Hills would therefore drop dramatically with this development scenario.
In conclusion, this proposed housing development would seriously degrade the ability of Segment 3, and all segments farther west, to continue supporting target species, including mountain lion and bobcat. This would have cascading effects on flora and fauna in segments farther west, especially when considered in context with the relatively small and edge-effected Segments 4 and 5 it connects to on the west. Mule deer populations may, at least temporarily, increase in westerly segments like the Whittier Hills, due to removal of mountain lions from the system. In the short term, this may result in increased car-deer collisions on local roads; but in the long term, even deer are likely to disappear from all segments west of Highway 57 due to isolation of this relatively small population.
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area (northeast of the Firestone Scout Reservation), although supporting some target species and other wildlife, is mostly open grassland and somewhat degraded in habitat quality. Although a reservoir confined to this upper area would incrementally reduce the size of this segment and its capacity to support target species populations, it is far enough removed from the primary corridor connection across the Missing Middle that it would have less effect on overall corridor function than other developments I considered. However, any development (for reservoirs or other purposes) in middle and especially lower Tonner Canyon could have severe impacts on corridor function, especially if they reduced use of the Tonner Canyon Bridge on Highway 57.
Any development that blocked access to or through the bridge area would make Highway 57 a barrier to wildlife and likely lead to wildlife extirpations in segments farther west.
At the very least, creation of these reservoirs would incrementally reduce the size of what is now a large Chino-Tonner subcore. Tonner Canyon, representing the westernmost portion of this subcore, is the primary source habitat for animals dispersing into the rest of the corridor system to the west. Hence, the location of this project would magnify its relative impact on continued corridor function by increasing the distance wildlife would have to move from source habitat areas to other segments.
Proposed City of Industry Road
Figure 6 also shows an approximate, conceptual alignment for a proposed road parallel to Tonner Canyon (see also Maps 1 and 2). Although I found no specifications for this road or associated development, it would appear to be a major throughway connecting Highway 57 (from the existing Tonner Bridge intersection) to Highway 60 across the widest portion of the PuenteChino Hills Wildlife Corridor. Based on its location, the road would require major cut and fill to construct. Perhaps most troubling is its connection at the critical Tonner Bridge wildlife undercrossing. Depending on design, this is highly likely to render this last remaining corridor connection non-functional for mountain lion, deer, bobcat, and numerous other species. Even if this connection could be engineered to retain a functional wildlife undercrossing, the road could severely impact wildlife populations and movements along a broad front. A series of additional undercrossings (or overcrossings) and extensive wildlife fencing would need to be incorporated along the length of the road, or else most of Tonner Canyon would be isolated between two barrier roads (this one and Highway 57) or wildlife would suffer severe roadkill impacts.
Approximately 21.2 sq. km of grasslands, forests, and shrublands would be segregated from the large and valuable Chino-Tonner subcore, incrementally diminishing its capacity to support wildlife populations. At best, what is now a broadly contiguous block of habitat would be reduced to a narrow and more edge-effected funnel across the Olinda Landfill to the Tonner Bridge.
Cumulative Effects
A full impact analysis for any or all of these proposed projects would need to address cumulative impacts on wildlife populations and movements through the corridor, which is beyond the scope of this report. Among these cumulative impacts would be inducement of further development, Puente-Chino “Missing Middle” Analysis
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such as additional residential, commercial, or industrial development along the road. Increased traffic (and hence roadkill) would also need to be analyzed and mitigated for. Any combination of two or more of these projects would likely render the Puente-Chino Hills Wildlife Corridor non-functional west of Olinda Landfill, regardless of mitigation.
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Discussion
Before summarizing conservation and restoration recommendations for the Missing Middle, this section reviews the literature on the functions and benefits of wildlife corridors in conservation, including criticisms of corridor conservation.
Functions and Benefits of Wildlife
Corridors
Landscape linkages and wildlife movement
corridors vaulted to the forefront of conservation
thinking in recent decades, in response to rising recognition that habitat fragmentation is a principal cause of species extinction and endangerment (Willis 1974, Diamond 1975, Wilson and Willis 1974, Noss 1983, Wilcox and Murphy 1985, Forman 1991, Harrison 1992, Rosenberg et al. 1997). Habitat connections or movement corridors connecting reserves or larger “core areas” of habitat are thought to counter many adverse effects of isolation by fragmentation on species and ecological processes (Preston 1962, Noss 1983, 1987, Soulé 1991, Meffe and Caroll 1994, Rosenberg et al. 1997, Soulé and Terborgh 1999, Beier et al. in press). Although some critics have argued that there are costs as well as benefits to conserving corridors, and that under certain circumstances creating or maintaining corridors could even harm some species or communities (e.g., Simberloff and Cox 1987, Simberloff et al. 1992, Hess 1994), the overwhelming weight of scientific evidence is that maintaining connectivity is generally beneficial, especially for those species and ecological communities for which connectivity “is the natural state of things” (Soulé and Terborgh 1999). Certainly, for most species and ecological communities, maintaining connectivity is less risky than losing connectivity (Hobbs 1992, Beier and Noss 1998, Soulé and Terborgh 1999).
Assessing Connectivity Pros and Cons
This section reviews specific arguments for and
against conserving corridors and how they apply to the
Puente-Chino Hills. As elaborated below, in most
cases, arguments against corridor conservation are
really just cautions against applying corridors as a
panacea for conservation, in recognition that there may be special cases where connecting reserves could cause more harm than good or where other approaches to conservation may be more effective or cost-effective (for example, enlarging core reserves rather than connecting existing reserves). These special cases do not apply to the Puente-Chino Hills Wildlife Corridor, where maintaining connectivity would clearly provide net benefits for biological diversity and ecosystem health in these hills. Given that the weight of scientific evidence favors connectivity here, whether and how connectivity can be assured is a societal issue not addressed in this scientific treatment. “Those who would destroy the
last remnants of natural
connectivity should bear the
burden of proving that corridor
destruction will not harm target
populations.”
Paul Beier & Reed Noss (1998)
“Connectivity is not just another
goal of conservation: it is the
natural state of things.”
Michael Soulé & John Terborgh (1999)
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The potential disadvantages of creating or maintaining wildlife movement corridors include several ecological arguments and one financial argument (Simberloff and Cox 1987, Simberloff et al. 1992, Hobbs 1992, Hess 1994):
1. Corridors may serve as conduits for the spread of deleterious species, like invasive pests, weeds, or predators.
2. Corridors may serve to spread detrimental processes—such as wildfire or disease—to or among reserve areas.6
3. Corridors may facilitate movements by highly mobile animals between reserves even without corridors. (Or, these species may be overly abundant in urban interface areas due to imbalanced ecological conditions.) But corridors may not help movement for more sedentary or at-risk species, for which other conservation approaches may work better than corridors.
4. Corridors could act as population “sinks” (Pulliam 1988), attracting individuals from higher quality habitat areas into edge-effected habitats where death rates exceed birth rates. If this effect is strong enough, it can reduce the regional abundance of the species, or even increase extinction probabilities for a rare species.
5. Corridors may be expensive to create or maintain and may not represent the optimal allocation of limited funding relative to, for example, increasing the size or management of existing core areas.
Note that in one way or another, all of these potential disadvantages hinge on relative comparisons of potential risks and benefits of maintaining vs. losing connectivity. Also, as pointed out by numerous researchers, the risks and benefits of corridors will vary by species. In the sections below, I briefly evaluate these potential disadvantages as they may apply within the Puente-Chino Hills Wildlife Corridor for target species of interest.
Conduits for Deleterious Species
It is difficult to envision how any deleterious species might increase its distribution or adverse effects due to conserving additional lands in this existing archipelago of open space reserves.
Connecting these areas with additional conservation would not increase rates with which annual weeds, Argentine ants, rats, house mice, or other potential pest species invade open space areas relative to existing conditions. Sources of such deleterious species are nearly ubiquitous in Southern California, due to existing human land use patterns. Maintaining an existing open space corridor system would not facilitate expansions of such species, either from the more urbanized western portions of the study area into the Santa Ana Mountains, or vice versa, and may even help counter further invasions (relative to more roads or development in the area).
6 Although wildfire and disease are natural disturbance processes in ecosystems, changes wrought by humans, such as habitat fragmentation and increased fire frequencies in urban interface areas, may create situations where these natural processes cause unnatural harm to biological resources. Corridors could help spread these deleterious effects.
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Conduits for Deleterious Processes
Again, it is difficult to conceive how maintaining connectivity in this context could contribute to the spread of deleterious processes. This argument is generally based on the assumption that a new corridor is being created (e.g., connecting what are naturally unconnected habitat areas) rather than maintaining “the natural state of things” with an existing, natural corridor (Beier and Noss 1998). As with the argument concerning deleterious species, this seems not to be an issue for the Puente-Chino Hills Wildlife Corridor. Although diseases or parasites may be carried between habitat segments by wildlife, this already occurs and always did. Although fires may spread from one segment to another under certain conditions, the area is already highly segmented by fire breaks in the form of existing roads and other discontinuities. In fact, given the nature of Southern California’s most destructive wildfires, which are driven by Santa Ana wind conditions (Keeley and Fotheringham 2001, Keeley et al. 1999, Halsey 2004), fire provides a stronger argument for not building more homes in wildland areas, rather than an argument for not conserving wildland areas.
Ineffectiveness for Rare or Sedentary Target Species
This is clearly a non-argument for the Puente and Chino Hills. Target species selected for review in this report, including both rare and common species, are highly sensitive to habitat fragmentation and benefit from corridor conservation (e.g., Beier 1993, Beier et al. in press, Crooks 2002, Ng et al. 2004). Although some rare or more sedentary species may not benefit directly from corridor conservation here (e.g., some reptile and amphibian species already lost from western segments of the corridor), the ecological benefits that accrue from corridor conservation for the remaining flora and fauna are indisputable. Indeed, research in the PuenteChino Hills Wildlife Corridor reinforces other research indicating that more common, insensitive, and “pesky” wildlife like skunks and raccoons actually increase in density with reductions in larger carnivores like mountain lions and bobcats, due to losses of landscape connectivity (Haas 2000, Crooks and Soulé 1999). Countering this process of “meso-predator release” (Crooks and Soulé 1999), and the cascade of species losses and other adverse ecological changes that it can bring, is a strong argument for maintaining the Puente-Chino Hills Wildlife Corridor for mountain lions, coyotes, and bobcats.
Population Sinks
This is a legitimate argument that deserves analysis. It may be that, especially for species highly prone to roadkill, mortality in the Puente and Chino Hills is elevated relative to larger, more contiguous areas like the Santa Ana Mountains. It is conceivable that the corridor therefore serves as a “population sink” (Pulliam 1988), where animals enter the corridor from larger or higher quality habitats, only to be killed. However, the potential for this effect to substantially reduce regional wildlife populations in the Santa Ana Mountains seems remote. Moreover, the benefits of these species living within the Puente and Chino Hills, even with elevated mortality rates, are immense, both to ecological health and to quality of life for local human residents.
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Suboptimal Conservation Investment
This is a non-argument for this study area. Given the current wildland-development pattern that exists, there is no alternative to corridor conservation and restoration for retaining species populations and maintaining healthy ecological processes in this area. Although one could argue that further investment in conserving these hills could be better spent elsewhere (e.g., enlarging larger wilderness reserves in Southern California mountains), this would come at the detriment of maintaining a unique ecological classroom full of wildlife in close proximity to millions of people craving a connection with nature. According to the California Department of Parks and Recreation, nearly a quarter billion dollars have already been spent on open space conservation in the Puente and Chino Hills, and this investment could be for naught if additional conservation fails to secure a continuous corridor from the Santa Ana Mountains to the Whittier Hills.
Mitigating Road Effects
Roads or the traffic they carry kill animals directly
(roadkill), disrupt natural migration and movement
patterns, interfere with species communication, change
water runoff and flow patterns, and create air, water, and soil pollution (Trombulak and Frissell 2000, Forman and Deblinger 2000, Jones et al. 2000, Reijnen et al. 1997). During Beier’s (1993, 1995) study of mountain lions in the Santa Ana Mountains, vehicles killed 33% of the population, including four lions killed at one road-crossing during a 2-year period.
The growing awareness of road impacts on environmental health and imperiled species has created a burgeoning literature on efforts to mitigate these effects with improved wildlife roadcrossing structures. Wildlife crossing structures have proved successful in the United States and elsewhere (Transportation Research Board 2002). The main types of structures, from most to least effective, are vegetated land-bridges, bridges, underpasses, and culverts.
About 50 vegetated wildlife overpasses, ranging from 50 m (164 ft) to over 200 m (656 ft) wide, have been built in Europe, Canada, and the U.S. (Evink 2002, Forman et al. 2003). Soil (0.5 to 2 m deep) covers the overpasses, which are planted, usually with native vegetation (Jackson and Griffin 2000). Overpasses are quieter than underpasses and maintain ambient conditions (Jackson and Griffin 2000), so they may be less intimidating for some species than dark tunnels.
In Banff Provincial Park, large mammals preferred overpasses to other crossing structures (Forman et al. 2003). Similarly, birds, butterflies, and other open-air wildlife are more likely to use overpasses than underpasses.
Bridges are also effective crossing structures, especially if wide enough to permit growth of both riparian and upland vegetation along stream banks (Jackson and Griffin 2000, Evink 2002, Forman et al. 2003). Bridges with greater openness ratios are generally more successful than low bridges and culverts (Veenbaas and Brandjes 1999, Jackson and Griffin 2000). The Tonner Bridge is a good example of a broad, open bridge with natural vegetation beneath. My observations reinforce those of previous biologists that maintaining access through this structure, “Nothing is worse for sensitive
wildlife than a road.”
Reed Noss
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and perhaps improving habitat conditions on either side, is critical to the flow of large mammals across the Puente-Chino Hills landscape.
Although inferior to bridges, culverts and other tunnel-like structures can be effective for some species (Jackson and Griffin 2000). Only very large culverts (such as box culverts and equestrian tunnels) are effective for large mammals (Lyren 2001, Haas 2000, Gloyne and Clevenger 2001). Gloyne and Clevenger (2001) suggest that underpasses for ungulates should be at least 4.27 m high and 8 m wide, with an openness ratio of 0.9 (where the openness ratio = height x width/length). Earthen flooring is preferable to concrete or metal (Evink 2002).
In places where a bridged, vegetated under-crossing or over-crossing is not feasible, placing pipe culverts alongside box culverts can help serve movement needs of both small and large animals.
Special crossing structures that allow light and water to enter the structure have been designed to accommodate amphibians.
Noise, artificial night lighting, traffic noise, and other disturbances can deter animal use of a crossing structure (Yanes et al. 1995, Clevenger and Waltho 1999, Forman et al. 2003). Shrub or tree cover can help funnel wildlife to a passage while hiding them or making them feel more secure when approaching crossing structures (Evink 2002, Forman et al. 2003). Regardless of crossing type, wildlife fencing is necessary to funnel animals towards road-crossing structures and keep them off the road surface (Falk et al. 1978, Ludwig and Bremicker 1983, Feldhammer et al. 1986, Haas 2000, Lyren 2001, Forman et al. 2003). Earthen one-way ramps can allow animals that wander into the right-of-way to escape over the fence (Bekker et al. 1995, Forman et al. 2003).
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Conclusions and Recommendations
Conservation and Restoration Priorities for the Missing Middle Based on the analysis of corridor function, Map 3 shows locations of priority conservation and restoration actions in and near the Missing Middle. This is by no means a comprehensive summary of all necessary and sufficient actions to maintain or improve biological conditions throughout the Puente-Chino Hills landscape. Rather, it focuses on those locations and actions that seem most critical to maintaining functional connectivity across the Puente-Chino Hills Wildlife Corridor based on the metapopulation analysis.
These recommendations are redundant with those from previous studies, especially concerning the need to secure and improve unimpeded movement by large target species across roads. This should not be surprising, because information on the characteristics and functioning of these corridor segments is quite consistent across studies. Perhaps the greatest benefit of the metaanalysis provided in this report is a renewed focus on the need to conserve not just unimpeded movement, but an archipelago of relatively large habitat blocks with sufficient carrying capacity to ensure continued presence of viable populations through this range of hills. Road-crossings are just one part of the story.
Priority Conservation Lands
Conserving intact habitat blocks within the red-hatched lands on Map 3 is essential to maintaining functional metapopulation dynamics for target species throughout the Puente-Chino Hills Wildlife Corridor. As supported by the geographic unit analysis, the capacity of Segments 2 and 3—from Chino Hills State Park to Harbor Boulevard—to support robust populations of target species and live-in habitat for mountain lions is essential to keeping these species in the study area, all the way to Whittier Hills. Essentially all of the Shell-Aera property, and at least the lower 1/2 to 2/3 of the City of Industry lands in Tonner Canyon, are of high priority for conservation.
Note that the line separating high-priority conservation lands in mid- to lower Tonner Canyon from upper Tonner Canyon is somewhat arbitrary. But the farther up Tonner Canyon one goes, the less essential habitat becomes for ensuring corridor functionality. (Note, however, that Cooper [2000] considered upper Tonner Canyon a high conservation priority for native birds, especially grassland species like raptors and grasshopper sparrows.) I established the northeast boundary of the Tonner Canyon high-priority conservation area primarily to consolidate a contiguous reserve along with the existing Firestone Scout Reservation and Chino Hills State Park. Extending this boundary farther north would increase biological benefits even more, but with decreasing marginal returns for corridor function.
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Map 3. Conservation and restoration priorities in the vicinity of Missing Middle.
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Essentially all of the Shell-Aera property west of Highway 57 is extremely high priority for conserving corridor integrity. Based on metapopulation analysis, conserving a “move-through corridor” across this property, as depicted in Figure 5, is not enough to ensure continued target species presence through the corridor system. Given this segment’s location between two nearbarrier roads, and the relatively narrow and constrained status of Segments 4 and 5 to the west, securing a large, intact habitat block capable of supporting populations or subpopulations of target species is essential here. Moreover, this segment could benefit greatly from habitat management and restoration to increase carrying capacity for target species, and thereby to decrease the probability of species extirpations here and all the way to the Whittier Hills.
Priority Crossing Improvements
Map 3 shows five priority road-crossing improvements with magenta circles, labeled A through E from east to west. Most of these recommendations have already been made by others (e.g., Haas 2000), and some may already have been acted on or are in planning stages. At the risk of redundancy, I nevertheless recommend the following improvements in these general locations.
Refer to Haas (2000) for additional recommendations and details:
A. Add wildlife fencing on either side of Carbon Canyon Road to reduce roadkill and encourage wildlife to use existing culverts, especially the concrete box culvert near the entrance to Chino Hills State Park. Adding another wildlife crossing structure, designed to accommodate all large mammals, would be even better. Given that traffic on this 2- lane road is increasing due to increasing development in the vicinity (Haas 2000), any future road upgrades should incorporate bridges or other very open wildlife crossing structures as mitigation. A variety of smaller under-crossings with funneling fences, specifically designed to accommodate smaller reptiles, amphibians, and mammals, should also be considered to improve connectivity for these species.
B. Prohibit any development that would increase traffic under the Tonner Bridge or add any new impediments (structures, lights, noise, etc.) to the vicinity of the bridge. Restore riparian vegetation along Tonner Creek, where degraded by oil development activities.
Fence along Highway 57 if monitoring suggests road mortality is high.
C. A wildlife underpass tunnel is to be constructed here under Harbor Boulevard, but recommended fencing has apparently not been allowed by a property owner (A.
Henderson, personal communication). Secure rights to install wildlife fencing along both sides of Harbor Boulevard to reduce roadkill and ensure maximum utility of the wildlife tunnel. Plant native shrubs and trees on either side of the tunnel to provide cover to wildlife approaching the entrances. Consider adding smaller under-crossings and funneling fences to accommodate smaller reptiles, amphibians, and mammals.
D. Secure remaining “at-risk” parcels in this narrow, constricted portion of the corridor, west of Powder Canyon and Schabarum Regional Park. Enlarge or otherwise improve the existing equestrian tunnel to enhance its use by wildlife, including adding screening Puente-Chino “Missing Middle” Analysis
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vegetation, especially on the western end. Fence either side of the tunnel to help funnel wildlife to it. However, extensive fencing along Hacienda Boulevard is not recommended, because most large mammals currently cross at-grade. Although Hacienda Boulevard currently has moderate traffic at relatively low speeds, and therefore relatively low roadkill (Haas 2000), road improvements or increases in traffic could make the situation worse. In this case, consider building a wildlife overpass (a vegetated wildlife bridge) over Hacienda Boulevard, taking advantage of steep slopes rising up from either side of the road. Given this terrain, a vegetated overpass somewhere between Skyline Drive and the equestrian tunnel may be feasible and would certainly be superior to culverts or other underpass structures in accommodating wildlife movement. Consider also adding smaller under-crossings and funneling fences to accommodate smaller reptiles, amphibians, and mammals.
E. Maintain and improve the Colima Service Tunnel as a critical wildlife underpass. Add fencing or screening vegetation, if necessary, based on further site-specific inspection or monitoring. Limit and mitigate for any actions that may increase traffic, light, noise, or human activity in the vicinity of the Service Tunnel from sunset to sunrise, when wildlife use is most frequent. Consider also adding smaller under-crossings and funneling fences to accommodate smaller reptiles, amphibians, and mammals.
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Exhibit C
Exhibit D
Exhibit E
Exhibit F
Exhibit G
manatt
404613130.1
March 27, 2026
VIA EMAIL ([email protected])
City of Brea
Planning Division
1 Civic Center Circle
Brea, CA 92821
Re: General Plan Comments for Brea 2050: Focused GPU and BCSP (State Clearinghouse No. 20250811123)
To Whom It May Concern:
This firm represents Sycamore Development Brea Canyon LLC and its affiliates (“Sycamore”), and we submit this letter on Sycamore’s behalf in connection with the City of Brea’s (“City”) Brea 2050: Focused General Plan Update (“2050 GPU”).1
Sycamore owns a significant amount of real property within the County of Orange (“County”), and certain of that real property is wholly or partially within the City’s Sphere of Influence (“SOI”) as shown in the 2050 GPU. Specifically, Sycamore owns approximately 321 acres located east of Brea Canyon Road and north of State Route 57 (hereinafter, the “CA-57 North Property”)2 and approximately 297 acres of property located south of Valencia Avenue and east of Carbon Canyon Road (hereinafter, the “Carbon Canyon Property”).3 The County
currently holds jurisdiction over the CA-57 North Property in its entirety and the majority of Carbon Canyon Property.
The CA-57 North Property, along with Sycamore’s adjacent lands in County of Los Angeles, is presently developed with more than 100 well sites, produces approximately 155 barrels of oil and 200 million cubic feet of natural gas per day, and is blanketed by an extensive network of production infrastructure, including tank facilities, processing facilities, service roads, and power lines. Additional industrial activities, including truck rental and servicing operations, also take place on the CA-57 North Property. The CA-57 North Property is designated for “Hillside Residential” in the City’s operative general plan adopted in 2003 (“2003 General Plan”), and the 2050 GPU proposes to maintain this Hillside Residential designation as to the CA-57 North Property.
1 The 2050 GPU was first made available to the public on February 12, 2026. 2 The CA-57 North Property is more specifically identified as parcel numbers 304-151-05, 304-151-10, 304-151-12, 304-151-14, 304-151-17, 304-151-18, 304-151-19, 304-151-69, 304-171-03, 304-171-06, 304-171-07, 304-171-08, 306-011-01, 306-011-02, 306-011-03, 306-012-12, 306-012-13, and 306-013-01. 3 The Carbon Canyon Property is more specifically identified as parcel numbers 308-021-15, 308-021-21, 308-011- 20, 308-011-22, 315-081-09, 312-011-18, 312-011-19, 322-031-29, 322-041-24, 322-051-12, 326-011-03, 326-011-
04. City of Brea Planning Division
March 27,2026