June 15, 2022
6 The inventory data collected suggests the following
maintenance recommendations which should be
verified by staff.
1. Grid trim schedule to prune all trees on a routine
cycle (Most agencies average between 3 to 5
years).
2. Initiate inspection and mitigation for trees
identified to need patrolling for disease or
decline.
3. Removal plan (evaluate WCA, Inc.
recommendations and determine the agency’s
priorities for phased removals or other
mitigation).
4. Planting plan to fill vacant sites.
5. Provide young tree maintenance to ensure
proper establishment.
CONCLUSION
This information is considered to be a valuable reference for future budget and maintenance projections. Your Area
Manager and WCA, Inc. can help you create these
projections.
PLANTING
Tree Planting (379 sites)
Based on the criteria provided by the City, WCA, Inc. identified 379 vacant sites that are suitable for planting. Identification of vacant sites during the inventory collection allows the agency to expand the urban forest and may assist in obtaining additional grant funding. Vacant site listings from the inventory can be generated to create work lists and utilized for budget projections. The planting palette should be referenced when determining the appropriate species to plant based on the concept of “right tree, right place.”
City of San Luis Obispo Community Forest Plan
PROFESSIONAL PROJECT REPORT
–
CITY & REGIONAL PLANNING
DEPARTMENT
CALIFORNIA POLYTECHNIC
STATE UNIVERSITY,
SAN LUIS OBISPO
–
JUNE 2022
City of San Luis Obispo Community Forest Plan C. Hamma
Professional Project Report: Master of City & Regional Planning Program Page 2 of 91 This report was prepared for the City of San Luis Obispo, California in partial fulfillment of the requirements for the Master of City & Regional Planning degree program, Department of City & Regional Planning, California Polytechnic State University, San Luis Obispo.
Christopher C. Hamma
June 2022
Cover photos by Christopher Hamma
Top left: The “Moon Tree” coast redwood, Mission Plaza
Bottom left: Coast live oak woodland below Bishop Peak
Middle right: San Luis Obispo City Hall, 990 Palm Street
City of San Luis Obispo Community Forest Plan C. Hamma
Professional Project Report: Master of City & Regional Planning Program Page 3 of 91 Acknowledgments
The author is grateful to the following individuals for their contributions to this document:
Graduate Committee:
Mike Boswell, Cal Poly San Luis Obispo – City & Regional Planning Department Bob Hill, City of San Luis Obispo – Office of Sustainability and Natural Resources Rodney Thurman, Heritage Tree Arboricultural Consulting Interviewees and Other Individuals Consulted:
Joe Carotenuti, Historian
Michael Codron, City of San Luis Obispo
Ron Combs, City of San Luis Obispo (retired)
Kim Corella, CAL FIRE San Luis Obispo
Greg Cruce, City of San Luis Obispo
Thomas Kessler and volunteer staff, History Center of San Luis Obispo County Jeff Reimer, Cal Poly San Luis Obispo
Matt Ritter, Cal Poly San Luis Obispo
Nathan Slack, City of Santa Barbara
Bettina Swigger, Downtown SLO Association
Rodney Thurman, Heritage Tree Arboricultural Consulting Matthew Wells, City of Santa Monica
Anthony Whipple, City of San Luis Obispo
Jenn Yost, Cal Poly San Luis Obispo
City of San Luis Obispo Community Forest Plan C. Hamma
Professional Project Report: Master of City & Regional Planning Program Page 4 of 91 Table of Contents
Acknowledgments.........................................................................................................................................3 Table of Contents..........................................................................................................................................4 I. Vision and Mission Statement ..............................................................................................................7 A. Vision.................................................................................................................................................7 B. Mission..............................................................................................................................................7 II. Executive Summary...............................................................................................................................8 III. Introduction ....................................................................................................................................10 IV. Methodology...................................................................................................................................12 A. Literature and Urban Forest Plan Review.......................................................................................12 B. Stakeholder Interviews...................................................................................................................12 C. Historical Archive Review................................................................................................................13 V. Literature Review................................................................................................................................14 A. Urban Forestry Overview................................................................................................................14 B. Valuation of Ecosystem Services.....................................................................................................16 C. Carbon Sequestration and Storage.................................................................................................17 D. Urban Heat Island Effect.................................................................................................................18
1. Urban Tree Canopy .....................................................................................................................19
2. Public Health...............................................................................................................................19
3. Energy Use ..................................................................................................................................20
4. The Urban Heat Island Effect and Equity ....................................................................................22
5. Conclusion...................................................................................................................................22 E. Tree Planting Initiatives ..................................................................................................................22 F. Equity ..............................................................................................................................................23 VI. Historical Context............................................................................................................................25 VII. Policy Context .................................................................................................................................32 A. General Plan Policies.......................................................................................................................32 B. Municipal Code (2021)....................................................................................................................33 C. 2021-2023 City Goals......................................................................................................................34 D. Climate Action Plan for Community Recovery (2020) ....................................................................35 E. Conservation Guidelines for Open Space Lands (2002)..................................................................35
City of San Luis Obispo Community Forest Plan C. Hamma
Professional Project Report: Master of City & Regional Planning Program Page 5 of 91 F. Multi-Jurisdiction Local Hazard Mitigation Plan (2019) (Lead Agency: San Luis Obispo County)..36 H. Downtown Concept Plan (2017) and Mission Plaza Concept Plan (2017)......................................37 I. Presidential Executive Order on Strengthening the Nation’s Forests, Communities, and Local Economies (2022) ..........................................................................................................................37 VIII. New Urban Forestry Contracts (2021)............................................................................................38 A. Maintenance ...................................................................................................................................38 B. Tree Inventory.................................................................................................................................38 C. Urban Forestry Organizational Assessment....................................................................................38
1. Findings.......................................................................................................................................38
2. Recommendations......................................................................................................................39 IX. Key Findings of Stakeholder and Technical Expert Interviews .......................................................40 A. Ensure Adequate Funding...............................................................................................................40 B. Ensure Adequate Staffing ...............................................................................................................41
1. City Employees vs. Contractors...................................................................................................42
2. Management...............................................................................................................................42
3. Volunteer Labor ..........................................................................................................................43
4. Location within City Organization...............................................................................................44 C. Complete Program Analysis and New Tree Inventory; Accrue and Analyze Data..........................44
1. Targets ........................................................................................................................................45
2. Metrics........................................................................................................................................46
3. Data Analysis...............................................................................................................................46 D. Strengthen Maintenance Practices and Clear the Backlog.............................................................47 E. Increase New Plantings...................................................................................................................48 F. Focus on Sustainability....................................................................................................................49
1. Right Tree, Right Place ................................................................................................................49
2. Lifecycle Perspective...................................................................................................................50
3. Climate Readiness.......................................................................................................................52
4. Diversity ......................................................................................................................................53
5. Pests and Disease........................................................................................................................53
6. Municipal Tree Lists....................................................................................................................55
7. Tree Committee ..........................................................................................................................56
8. Soil and Infiltration Enhancement ..............................................................................................57
City of San Luis Obispo Community Forest Plan C. Hamma
Professional Project Report: Master of City & Regional Planning Program Page 6 of 91
9. Safety ..........................................................................................................................................59
10. Water Conservation................................................................................................................60 G. Address Issues Unique to Downtown .............................................................................................61
1. Downtown Concept Plan and Mission Plaza Concept Plan.........................................................61
2. Downtown’s Big Trees ................................................................................................................62 H. Increase Outreach to Officials and the Public.................................................................................63 I. Address Equity Issues......................................................................................................................64 X. Goals ...................................................................................................................................................66 XI. Recommendations..........................................................................................................................67 A. Funding ...........................................................................................................................................67 B. Staffing ............................................................................................................................................67 C. Complete Program Analysis and New Tree Inventory; Accrue and Analyze Data..........................68 D. Strengthen Maintenance Practices and Clear the Backlog.............................................................68 E. Increase New Plantings...................................................................................................................69 F. Focus on Sustainability....................................................................................................................70 G. Address Issues Unique to Downtown.............................................................................................73 H. Increase Outreach to Officials and the Public.................................................................................74 I. Address Equity Issues......................................................................................................................75 XII. Next Steps.......................................................................................................................................76 XIII. References ......................................................................................................................................77
City of San Luis Obispo Community Forest Plan C. Hamma
Professional Project Report: Master of City & Regional Planning Program Page 7 of 91 I. Vision and Mission Statement
A. Vision
The City of San Luis Obispo and its residents serve as the proud stewards of a vibrant, welcoming, climate-resilient urban forest that maximizes the environmental, social, and economic benefits provided by trees. The City works hand in hand with a variety of partners, including community groups and contractors, to ensure that public streetscapes, parks, riparian corridors, and open spaces support a diverse, thriving tree canopy that improves quality of life for all in San Luis Obispo, both now and decades into the future.
B. Mission
The mission of the City of San Luis Obispo Community Forest Plan (CFP) is to achieve the stated Vision by working with and empowering city residents and partners to establish innovative, science-grounded goals and strategies to protect, expand, and nurture the City’s public tree cover and the associated benefits over the coming decades.
Roughly 60-year old Indian laurel fig (Ficus microcarpa) trees along Higuera Street in downtown San Luis Obispo. Photo by Christopher Hamma.
City of San Luis Obispo Community Forest Plan C. Hamma
Professional Project Report: Master of City & Regional Planning Program Page 8 of 91 II. Executive Summary
The City of San Luis Obispo has identified protection and expansion of the city’s urban forest as a Major City Goal under its 2021-2023 Financial Plan. In addition, as one approach to achieving carbon neutrality by 2035, the City’s 2020 Climate Action Plan for Community Recovery (CAP) calls for increasing carbon sequestration in the urban forest through large-scale tree planting. As such, the CAP proposes preparation of the City’s first-ever urban forest master plan. This is an initial draft of that document – the City of San Luis Obispo Community Forest Plan.
Activities undertaken in the creation of this document included stakeholder interviews as well as review of academic literature, other cities’ forest master plans, and historical archives. The Urban Forest Organizational Assessment commissioned by the City and written by Davey Resource Group was also reviewed. A high-level summary of selected research results is provided here:
• The Urban Forest Organizational Assessment and the updated street/park tree inventory conducted by West Coast Arborists were important first steps in the CFP process.
• The City currently has approximately 14,000 publicly owned street and park trees. • Adequate long-term funding, staffing, and contractor management will be critical to addressing the multi-year tree maintenance backlog and ensuring preservation of existing, mature public trees in the city.
• The proposed effort to plant 10,000 new trees in the public right-of-way by 2035 (the 10 Tall initiative) will be essential for the creation of a healthy urban forest that serves future generations of city residents and visitors.
o The primary focus of 10 Tall will be planting native species in City open space and riparian areas, but streetscapes, parks, and private property also offer planting opportunities.
o The City will have to work closely with its external urban forestry partners and their volunteer labor resources to achieve the planting of 10,000 trees. o These groups will need the ability to access and edit the updated City tree inventory database for the purposes of recording new tree plantings. • Metrics and targets will need to be identified in order to evaluate progress toward goals.
o Examples of potential metrics include percent canopy cover, new tree survival rate, species and age diversity, and annual carbon sequestration and total storage.
City of San Luis Obispo Community Forest Plan C. Hamma
Professional Project Report: Master of City & Regional Planning Program Page 9 of 91 • The principles of diversity, equity, and inclusion (DEI) should inform the City’s tree management and planting activities.
o The City should consider analyzing tree canopy cover, impervious surfaces, and other land cover characteristics by neighborhood socioeconomic characteristics, to identify areas in which urban forest benefits may be inequitably distributed. • The City may want to consider improvements to the municipal code, engineering standards, and/or management practices around tree planting, removal permitting, and irrigation.
• Preparation of an urban tree lifecycle plan and a tree planting plan are recommended. • The City should update its Master Tree List based on ongoing research into climateready urban tree varieties, which are chosen for their tolerance to challenging urban soil conditions, high heat and aridity, and pests/disease among other factors. • The role and authority of the City Tree Committee should be reexamined. • The City must continue to assess the urban forest through the lens of safety, in terms of wildfire, flood, and hazardous tree risks as identified in the General Plan Safety Element and the Multi-Jurisdiction Local Hazard Mitigation Plan. • The City should continue using a variety of outreach methods to foster interest in tree care and planting among the general public.
Carrot wood (Cupaniopsis anacardioides) trees along Chorro Street, downtown San Luis Obispo. Photo by Christopher Hamma.
City of San Luis Obispo Community Forest Plan C. Hamma
Professional Project Report: Master of City & Regional Planning Program Page 10 of 91 III. Introduction
Urban forests1 provide a myriad of environmental, social, and economic benefits to a city’s residents, visitors, and business owners (Dwyer et al., 1992; Tyrvainen et al., 2005; McPherson, 2006; Nowak, 2016; Janowiak et al., 2021). The “green infrastructure” provided by urban trees and landscaping cleans the air (Nowak et al., 2006), reduces flooding potential, noise, and wind (Bolund and Hunhammer, 1999; Livesley et al., 2016), cools our buildings through shading and evapotranspiration (Heisler, 1986; Ko, 2018; McPherson and Simpson, 2003), creates wildlife habitat (Strohbach et al., 2013), and fights climate change by storing greenhouse gases (GHGs) in the form of wood (Nowak and Crane, 2002).
Trees beautify our cities (Schroeder, 1989), increase traffic and pedestrian safety (Dumbaugh and Gattis, 2005), extend pavement life (Burden, 2006), enhance property values and increase business traffic (Burden, 2006; Staats and Swain, 2020), increase happiness and social interaction (Kwon et al., 2021; MacKerron and Mourato, 2013; Marselle et al., 2020), and reduce crime (Kuo and Sullivan, 2001; Schertz et al., 2021). They encourage us to engage in outdoor recreation, strengthening our physical and mental health (Dwyer et al., 1992; Pretty et al., 2005). Some trees warrant special treatment because they have outstanding traits or significant cultural value (Jim, 2017).
These ecosystem services are worth billions of dollars annually to the 83% of Americans who live in urban areas (University of Michigan Center for Sustainable Studies, 2021). Trees are a good investment as well – in California, every dollar put into street tree planting and care returns nearly $6 to its community in ecosystem services and increased property values (McPherson et al., 2016).
Yet despite growing recognition of the value created by urban forests, the United States is losing roughly 36 million trees each year due to causes including development, pests and disease, wildfires, and extreme weather (Nowak and Greenfield, 2018a). San Luis Obispo is vulnerable to these trends; the City’s roughly 14,000 public street and park trees (West Coast Arborists, 2022) are at present suffering from a multi-year backlog of deferred maintenance due to staff injuries, retirements, and the effects of the Covid-19 pandemic.
The San Luis Obispo City Council has declared maintenance and expansion of the urban forest to be among a suite of Major City Goals in the 2021-2023 Financial Plan (City of San Luis Obispo, 2022a). The Council has also expressed strong support for the City’s 2020 Climate Action Plan 1 While the term “urban forest” typically refers to all trees in a city, both public and private, privately owned trees usually comprise the large majority – perhaps 80 to 85 percent – of the total (Arbor Day Foundation, n.d.). Because local governments have limited influence over tree management on private property, the recommendations presented in this Community Forest Plan deal primarily with the City of San Luis Obispo’s publicly owned street, park, creek corridor, and open space trees.
City of San Luis Obispo Community Forest Plan C. Hamma
Professional Project Report: Master of City & Regional Planning Program Page 11 of 91 for Community Recovery (CAP) which calls for a new City tree inventory, strategies to revitalize ongoing tree operations and maintenance, and the planting of 10,000 new trees within the city by 2035 – as well as for the creation of this strategic Community Forest Plan (CFP; City of San Luis Obispo, 2022b). The CFP is intended to work together with the City’s General Plan, CAP, and other guiding documents to support City efforts to become carbon-neutral by 2035 and to adapt to the disruptive effects of a rapidly changing climate.
San Luis Obispo’s publicly owned urban forest contributes greatly to “the SLO life” and the high level of environmental quality enjoyed by residents and visitors alike. By highlighting the valuable benefits provided by the City’s urban trees, acknowledging the challenges faced in their care, and striving to include the public in adaptive management-based forest planning and activities, it is hoped that this Community Forest Plan and its future iterations will contribute to enhanced health and well-being in San Luis Obispo for many years to come.
Terrace Hill and Islay Hill beyond Court Street Plaza in downtown San Luis Obispo. Photo by Christopher Hamma.
City of San Luis Obispo Community Forest Plan C. Hamma
Professional Project Report: Master of City & Regional Planning Program Page 12 of 91 IV. Methodology
This draft of the San Luis Obispo Community Forest Plan (CFP) was written in partial fulfillment of the requirements for the Master of City & Regional Planning degree program at California Polytechnic State University, San Luis Obispo. Specifically, this document is intended to fulfill the program’s “culminating experience” requirement in the form of a professional project report.
Three research methods were employed in creation of the CFP: review of academic literature and other cities’ urban forest master plans, internal and external stakeholder interviews, and perusal of historical archives.
A. Literature and Urban Forest Plan Review
Review of peer-reviewed academic literature provides an important foundation for understanding the most pressing issues at hand in a given topic area. This work primarily involved online research, with information from hard copy sources comprising a minor portion.
Scientific and academic journal articles were located and accessed via the Cal Poly Robert E.
Kennedy Library’s electronic databases and via internet search engines. The latter were also used to locate and access relevant articles published on the web by popular media outlets including newspapers and periodicals.
Several other municipal urban forest management plans were also reviewed, including those from the Cities of Davis, San Francisco, Santa Barbara, and Santa Monica.
B. Stakeholder Interviews
Speaking directly with working professionals and academic researchers builds on the insights obtained via literature review by allowing the interviewer to tap into the latest real-world knowledge and management best practices and actions, and thus gain crucial understanding of the relationships between theory and practice.
Prospective CFP interviewees were contacted by e-mail and/or telephone. Those who expressed willingness to participate were provided with a list of interview questions and were asked to sign an informed consent document, as required by the Cal Poly Institutional Review Board (IRB). The informed consent requirement sets out the rights of human research subjects. In this case the informed consent assured participants that their responses to interview questions, when referenced within the document being written, would not be tied to any personally identifiable information. Interviews were conducted via the online video conferencing application Zoom or by telephone and ranged in duration from 30 to 60 minutes.
City of San Luis Obispo Community Forest Plan C. Hamma
Professional Project Report: Master of City & Regional Planning Program Page 13 of 91 C. Historical Archive Review
Two sources were queried regarding the availability of historical information pertaining to San Luis Obispo’s urban forest: the History Center of San Luis Obispo County’s research room, located on the lower floor of the old Carnegie Library adjacent to Mission Plaza, and the Reference section on the third floor of the current city library at 995 Palm Street in downtown San Luis Obispo. At the History Center, curated archival materials consisting of photocopied historical newspaper and magazine clippings were made available for review on the premises.
Similarly, at the public library various books and pamphlets about the city’s history were perused. In both locations, notes on articles of interest were taken by hand and a smartphone was used to photograph entire pages for later reference.
Murray Avenue’s unique tree-lined pedestrian median, San Luis Obispo. Photo by Christopher Hamma.
City of San Luis Obispo Community Forest Plan C. Hamma
Professional Project Report: Master of City & Regional Planning Program Page 14 of 91 V. Literature Review
A. Urban Forestry Overview
Urban forests are more important than ever in the face of increasing human population, increasing migration from rural to urban areas, and worsening impacts from pollution and global climate change (Tyrvainen et al., 2005). The “green infrastructure” provided by urban vegetation removes air pollution (Nowak et al., 2006); reduces flooding, erosion, noise, and wind (Bolund and Hunhammer, 1999; Livesley et al., 2016); gives us energy savings by cooling our homes and businesses (Heisler, 1986; Ko, 2018; McPherson and Simpson, 2003); provides wildlife habitat (Strohbach et al., 2013); and stores carbon that would otherwise go into the atmosphere (Nowak and Crane, 2002).
Trees beautify our cities (Schroeder, 1989), lead to increased outdoor social interaction and feelings of happiness and safety (Coley et al., 1997; Kuo et al., 1998; Kwon et al., 2021; MacKerron and Mourato, 2013; Marselle et al., 2020), help us recover from illness (Verderber and Reuman, 1987) and mental fatigue (Kaplan, 1995), increase property values (by an estimated 5%; Staats and Swain, 2020) and retail business traffic (Burden, 2006), and reduce crime (Kuo and Sullivan, 2001; Kuo et al., 2003; Leahy, 2015; Schertz et al., 2021). Parks and open space that contain urban trees often provide opportunities for public recreation (Dwyer et al., 1992; Pretty et al., 2005), and individual trees may have historic or other significant cultural value (Jim, 2017). Forests may even increase rainfall (Meier et al., 2021).
Yet even in the best of circumstances, cities present challenging conditions for tree growth and survival (Mullaney, 2015; Livesley et al., 2016; Nowak, 2016). Urbanization converts natural land cover to impervious surfaces, thereby changing natural drainage characteristics and inhibiting gas exchange and infiltration of water and nutrients into the soil. Additional obstacles to urban forest health include lack of planting locations and adequate growing space, soil compaction, high soil salinity and/or unfavorable pH, and high temperatures caused by the urban heat island effect. Trees can also be damaged by pollution such as contaminated stormwater runoff, the proliferation of invasive plants, vandalism, and physical interference from infrastructure.
These conditions can stunt trees and plants, limiting their health and lifespan (Lawrence et al., 2012); research has found that street trees have shorter lifespans than trees in more natural settings (Smith et al., 2019). The average lifespan of a street tree is estimated at 19 to 28 years; the survival rate of new plantings ranges from 94.9 to 96.5% (Roman and Scatena, 2011).
In fact, despite growing appreciation of the environmental, social, and economic benefits conferred by tree cover, the US is losing tree biomass and gaining impervious land cover each year due to urban and agricultural development, pests and disease, wildfires, and extreme weather; this trend has accelerated noticeably since the mid-1990s (Cohen et al., 2016). It is
City of San Luis Obispo Community Forest Plan C. Hamma
Professional Project Report: Master of City & Regional Planning Program Page 15 of 91 estimated that over the five-year period from 2009-2014, 1% of all urban trees in the US, or roughly 36 million trees on 175,000 acres, were lost (Nowak and Greenfield, 2018a). Although tree growth, natural regeneration, and tree planting associated with urban expansion counteract this trend to some extent, the net effect is a loss of percent urban tree cover.2 Furthermore, urban green spaces have traditionally been given relatively little consideration in deference to commercial, residential, and transportation development (Wolf, 2004). To the extent that municipalities assess their urban forest resources, they often take a narrowly focused approach by relying primarily on quantification of canopy cover (Kenney et al., 2011).
This approach is overly simplistic, making it unlikely that forest productivity and benefits will be accurately characterized. Further, a recent review found that municipal parks and recreation management agencies, stewards of many of the nation’s urban trees, are largely unprepared for the current and future effects of climate change (Cheng et al., 2021).
These facts point to the importance of both maintaining current urban forests and continually planning for (and planting) the next one in the contexts of greater urban populations and increasingly challenging climatic conditions. For forests and the benefits they confer to be considered “sustainable” (i.e., meeting today’s needs without compromising future generations’ ability to meet their own needs [Keeble, 1988]), the necessary conditions include a healthy tree and forest resource, community-wide support, and a comprehensive management approach (Clark et al., 1997). Success in meeting urban forestry goals is most likely in the presence of holistic, strategic forest planning and management practices that use frameworks of criteria and indicators like species and age diversity, condition of publicly owned trees, urban forest funding, staffing, legal tree protections, and management practices (Kenney et al., 2011).
Sustained outreach to the general public is crucial if success is to be achieved. For a taxpayerfunded program to achieve substantial public support, elected officials and residents must be convinced that the benefits provided are worth the costs (i.e., “Sustained political support of such investments is more likely if economic benefits can be demonstrated” [Wolf, 2004]).
Brief examinations of subtopics including carbon sequestration and storage, ecosystem services valuation, the urban heat island effect, tree planting initiatives, and equity are presented on the following pages.
2 This is a nuanced point. Although total area of urban tree cover is expected to increase as urban land cover expands, average percent tree cover in urban areas is projected to decline from 39.4% in 2010 to 32.8% in 2060 (Nowak et al., 2021). Even though newly developed land is often planted extensively with urban trees, in many cases these plantings do not offset the total amount of pre-existing tree cover that was removed, resulting in a net loss of canopy cover. This trend is predicted to continue indefinitely as long as urbanization is ongoing.
City of San Luis Obispo Community Forest Plan C. Hamma
Professional Project Report: Master of City & Regional Planning Program Page 16 of 91 B. Valuation of Ecosystem Services
Urban trees provide their many benefits in a more cost-effective way than human-made, “gray” infrastructure can (Nowak and Greenfield, 2018b). The value of just four urban tree-related ecosystem services in the United States is estimated at $18.3 billion annually, namely: air pollution removal ($5.4 billion), carbon sequestration ($4.8 billion), lowered building energy use ($5.4 billion), and avoided pollutant emissions ($2.7 billion). In California alone, $2.5 billion worth of street trees provide over $1 billion in ecosystem services to state residents each year, including the removal of 567,748 tons of CO2 annually, equivalent to taking 120,000 cars off the road (McPherson et al., 2016).
These dollar values can be significant at the city or metropolitan area level as well. For example, tree cover was estimated to have reduced stormwater storage costs by $4.7 billion and generated annual air quality savings of $49.8 million in a study of the Washington, D.C. metro area (Wolf, 2004). In another study, the USDA Forest Service calculated that the City of Santa Monica, California’s over 34,000 street and park trees are worth $155 million and deliver $5.1 million dollars' worth of benefits to the community annually (McPherson et al., 2015).
Drilling down to the individual tree level, the planting and first three years’ care of a single urban tree (cost range = $250 to $600) was reported to return over $90,000 in environmental benefits to its community (Burden, 2006). A 2002 study in Seattle, Washington reported that per-tree average annual net benefits were $1 to $8 for a small tree, $19 to $25 for a medium-sized tree, and $48 to $53 for a large tree (Wolf, 2004), although McPherson et al. (2016) reported a figure of over $110 per tree for this (tree size not specified) in California. Assuming an average annual tree management cost of $19, every dollar invested in tree planting or maintenance in California returns $5.82 to its community in ecosystem services and increased property values (McPherson et al., 2016).
Estimates of the value of ecosystem services are often based on contingent valuation methods.
Contingent valuation is a survey-based means of estimating the economic value of resources, often environmental benefits (for instance, air pollution removal) that are not typically traded in economic markets (Jones, n.d.). The results of these studies may be useful for outreach to elected officials and the public because they translate sometimes arcane, intangible concepts into a format that is readily understood by all – dollar value.
However, it is important to note that these often-impressive figures do not translate directly into revenue into the managing agency’s accounts, because they typically consist of avoidance of costs that would otherwise be borne by others. For example, if a city plants dozens of trees that eventually reduce household energy bills in a given neighborhood, the savings from those trees are realized by individual ratepayers, not by the city. On the other hand, from a broader perspective it can be argued that such projects have high value for all citizens because of the
City of San Luis Obispo Community Forest Plan C. Hamma
Professional Project Report: Master of City & Regional Planning Program Page 17 of 91 many co-benefits that become available as the trees grow, helping to justify the initial and operational taxpayer-based expenditures.
Table 1 categorizes the many advantages obtained from urban forests by category of recipient:
residents, visitors, business owners, or all people. Obviously, urban forest benefits are widely distributed and there is much overlap between categories; this simplified representation is only one person’s subjective interpretation.
Table 1. Urban Forest Benefits by Recipient Category.
Residents Visitors
Business
Owners
All
Air pollution removal x
Beautification/aesthetics x x
Carbon sequestration and storage x
Cooling and energy savings x
Flooding/erosion/stormwater runoff reduction x x
Food production (fruit, nut trees) x
Improved physical, mental, and emotional health x
Increased contentment/happiness x
Increased outdoor social interactions x x
Increased property value x 1x 1
Increased retail business traffic x
Increased traffic and pedestrian safety x
Longer pavement life x
Preserved historic or cultural significance x
Reduced crime x
Wildlife habitat x x
Wind and noise reduction x x
1 If a property owner
C. Carbon Sequestration and Storage
The Intergovernmental Panel for Climate Change (IPCC) has found unequivocal evidence that since the beginning of the Industrial Revolution, the mass combustion of hydrocarbons and resulting release of greenhouse gases (GHG) by human civilization has caused significant warming of Earth’s atmosphere and ocean and land surface temperatures at a rate unprecedented in at least the last 2,000 years (Allan et al., 2021). The observed results include more intense, prolonged, and/or frequent heatwaves, heavy precipitation, droughts, and tropical cyclones.
City of San Luis Obispo Community Forest Plan C. Hamma
Professional Project Report: Master of City & Regional Planning Program Page 18 of 91 Climate action planning incorporates numerous approaches to both reducing carbon emissions and strengthening communities’ resilience to the effects of climate change (Boswell et al., 2019). Carbon sequestration and storage, along with improvements in efficiency and conservation, replacement of fossil fuels with renewable energy sources, and waste reduction, is an important strategy for reducing GHG emissions (Boswell et al., 2019, pp. 161-162).
Trees and other woody vegetation act as a sink for carbon dioxide (CO2) by fixing carbon during photosynthesis and storing excess carbon as biomass; this carbon is not released into the atmosphere until the wood decomposes or is burned (Nowak and Crane, 2002). Globally, forests sequester nearly 3 billion tons of anthropogenic carbon every year through net growth, absorbing about 30% of all CO2 emissions from fossil fuel burning and net deforestation (Canadell et al., 2007).
As of 2002, urban trees in the coterminous USA were estimated to store 700 million tons of carbon with a gross carbon sequestration rate of 22.8 million tons of carbon per year (Nowak and Crane, 2002). The total monetary value of this storage was estimated at $14.3 billion, with an annual sequestration value of $460 million.
This carbon storage capacity will only become more important going forward. Currently, 83% of Americans live in urban areas (University of Michigan Center for Sustainable Studies, 2021), which experience high GHG emissions. Furthermore, the area of urban land cover in the US is expected to more than double from 27.4 million hectares in 2010 (3.6% of total land area) to
66.0 million hectares (8.6% of total land area) by 2060 (Nowak et al., 2021).
Given these facts, it is unsurprising that interest in tree planting initiatives (TPI) as a means of sequestering and storing carbon has increased dramatically over the past two decades (Eisenman et al., 2021). However, these activities may be either sinks or sources of carbon depending on a variety of factors. A 2015 evaluation of the Million Trees LA initiative found that the program appeared to be on track to becoming a net carbon sink, although success will ultimately depend on whether the projected 40-year avoided CO2 emissions from energy savings and biopower are realized, as well as what happens with the lumber and other organic debris from removed trees (McPherson et al., 2015). Regardless, the authors noted that opportunities exist in urban forestry to increase net reductions by reducing CO2 emissions from mulch decomposition, irrigation, water, equipment, and vehicles.
D. Urban Heat Island Effect
Air temperatures are often higher in a city than in its surrounding countryside; this phenomenon is known as the urban heat island (UHI) effect (Oke, 1982). Different areas within a city can experience differing spatial and temporal levels of UHI effect due to variations in land cover, urban geometry, and absorption and emittance of solar radiation (Kim and Brown, 2021).
City of San Luis Obispo Community Forest Plan C. Hamma
Professional Project Report: Master of City & Regional Planning Program Page 19 of 91 UHIs result from the conversion of natural land cover to urbanized surfaces (often impervious and dark-colored) and are increased by waste heat from buildings and vehicles (Stone et al., 2013). UHIs cause temperatures to rise by decreasing the availability of water for evaporative cooling, and by decreasing reflectance and increasing absorption of solar radiation.
The UHI effect is concerning for two primary reasons: its damaging effects on public health, and its contribution to increased energy demand (McDonald et al., 2020), both of which may be expected to increase in step with urban population growth. Furthermore, the UHI effect is exacerbated by global climate change and this effect is expected to continue (McPherson and Simpson, 2003; US Environmental Protection Agency, 2022). A study of California’s major cities found that extreme heat events and temperature variances are projected to increase faster than the rate of increase in mean temperature (Miller et al., 2008).
1. Urban Tree Canopy
Urban tree canopies moderate the UHI effect by reducing air and surface temperatures through shading and evapotranspiration (McDonald et al., 2020), and they do so in a very cost-effective way (Stone et al., 2013; Livesley et al., 2016). Urban tree coverage is associated with reduced temperatures at the city, neighborhood, street, and parcel scales, even in suburban areas with relatively lower impervious surface coverage than dense urban areas (Elmes et al., 2015).
Factors influencing the efficacy of tree cover in attenuating the UHI effect include land use types within the city, amount of impervious cover, tree location, tree density, prevailing winds, and other regional climate differences (McPherson and Simpson, 2003). Areas with vegetative cover and high-albedo (i.e., high-reflectivity) roofing and paving materials – referred to generally as ‘‘cool materials’’ – are associated with lower surface and near-surface air temperatures in contrast to sparsely vegetated areas with low-albedo (“dark”), impervious cover; this is due to increased evapotranspiration and/or an increase in reflected solar radiation (Stone et al., 2014).
Proper placement of trees is important for optimizing the benefits they provide (Heisler, 1986).
Locations that would block rooftop solar panels or would reduce heating by solar radiation during winter months should be avoided. In addition, attention must be given to species selection and water supply when UHI mitigation is a primary ecosystem service desired from an urban forest; for example, in one study Liquidambar styraciflua trees were found to be approximately 2.5 times as effective at cooling as Eucalyptus camaldulensis trees (Ballinas and Barradas, 2016).
2. Public Health
The UHI effect contributes to increased morbidity and mortality through dehydration, higher risk of illnesses such as heat stroke and heat exhaustion, exacerbation of existing cardiovascular,
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Professional Project Report: Master of City & Regional Planning Program Page 20 of 91 pulmonary, and renal diseases, and respiratory problems from greater exposure to ground-level ozone (Hsu et al., 2021; McDonald et al., 2020). High heat is also associated with loss of labor productivity and decreased learning (Hsu et al., 2021).
Many urban residents live in old, poorly insulated houses with little to no air cooling capacity, and therefore face increased risk of heat-related mortality or morbidity as the frequency and intensity of heatwaves increase due to climate change (Ko, 2018). This is especially true of vulnerable populations such as the elderly and the disabled.
Extreme heat is believed to cause an average of 12,000 deaths a year globally, although there is high year-to-year variation depending on weather conditions (McMichael et al., 2004). Heat waves are the leading weather-related killer in the United States (US Environmental Protection Agency, 2021), where estimates of average annual deaths from heat range from 600 (Sarofim et al., 2016) to 1,300 (Kalkstein et al., 2011). Current mortality rates from extreme heat are expected to more than double by the mid-to-late 21st century (Stone et al., 2014).
Achieving the 2°C maximum warming threshold called for in the Paris Agreement could avoid between 70 and 1,980 annual heat-related deaths per US city during extreme events (30-year return period) (Lo et al., 2019). Similarly, achieving the 1.5°C threshold could avoid between 110 and 2,720 annual heat-related deaths. One study researching heat-related mortality in three large US cities (Atlanta, Philadelphia, and Phoenix) found that vegetation and albedo enhancement could offset projected increases in deaths from heat by 40% to 99% across the three regions (Stone et al., 2014).
A study of urban tree cover across 97 American cities found that trees reduced heat-related mortality by an estimated 245 to 346 deaths annually at a value of $1.0 - $2.4 billion per year (McDonald et al., 2020). Extrapolated to all US urban residents, annual avoided mortality might be 1,030 - 1,454 deaths, valued annually at $5.3 - $12.1 billion.
Interestingly, however, while heat-related mortality is projected to keep increasing, the value of tree cover for reducing deaths seems to have declined significantly in recent decades due to increased use of air conditioning (McDonald et al., 2020).
3. Energy Use
The UHI effect increases demand for electricity, largely to power air conditioning, and can therefore increase carbon dioxide emissions from fossil fuel power plants (McPherson and Simpson, 2003; Nowak, 2016). UHIs also increase municipal water demand as residents attempt to keep landscaping alive.
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Professional Project Report: Master of City & Regional Planning Program Page 21 of 91 Trees can increase, decrease, or have little effect on energy use depending on general climate, building type, tree species, and tree location (Heisler, 1986). Tree shade reduces building energy demand for air conditioning by reducing solar radiation on walls and roofs and lowers ambient temperature through evapotranspiration; trees can also reduce heating demand by blocking wind (Ko, 2018).
The magnitude of reported energy savings varies widely depending on climate, method, data, and assumptions for buildings and trees. A building with adjacent trees uses 2.3% to 90% less cooling energy, mostly through shading effects, and 1% to 20% less heating energy through windbreak effects, in comparison to buildings without trees (Ko, 2018). A summary of research data suggests that the maximum potential annual effect of trees on energy use in conventional, single-family houses Is about 20 to 25% compared to the same house in the open (i.e., without nearby trees) (Heisler, 1986).
The density and spatial arrangement of the urban forest also affect the ability to obtain this cooling effect. The combined energy savings effect of many trees in an area is much greater than that from a single tree or a single heavily treed property on a mostly tree-free street (Heisler, 1986). When large trees are well distributed throughout a neighborhood, all of the trees together may have a significant impact on temperature and energy use in buildings, particularly in summer.
Consistent with most large U.S. cities, the vast majority of land cover change in the Atlanta metropolitan region in recent decades has occurred outside of the central-city core (Stone et al., 2013). Yet, despite this growth pattern, temperatures in the core have continued to increase at a higher pace than in nearby rural areas, resulting in rapid growth of the city-center heat island even in the absence of significant land use changes. Even so, suburban tree cover was found to provide a heat reduction benefit to nearby central city areas (Stone et al., 2013). Similarly, under calm wind conditions, the cooling benefit of a large park in the hot urban environment of Tokyo, Japan extended 200 meters downwind into surrounding neighborhoods (Sugawara et al., 2016).
As of 2003, in California approximately 177.3 million urban trees were reducing annual air conditioning energy use by 2.5% (roughly 6,400 GWh) for savings of $485.8 million, out of total tree-affiliated savings of approximately $778.5 million per year (McPherson and Simpson, 2003).
Yet, at the same time, 241.6 million empty planting sites were tallied (i.e., only 42% of all potential tree planting sites in California cities were filled). Planting 50 million trees to shade east and west walls of residential buildings was projected to reduce cooling need from air conditioning by 1.1% and peak load demand by 4.5% over a 15-year period (McPherson and Simpson, 2003). Given California’s high dependence on electricity imported from other states and ongoing episodes of power demand exceeding supply (resulting in, for example, rolling blackouts during heat waves), the above findings highlight an opportunity to improve grid stability and resilience.
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4. The Urban Heat Island Effect and Equity
Low-income and/or heavily minority-occupied urban neighborhoods in the United States contain significantly fewer trees and other landscaping, more impervious land cover (thus, fewer opportunities to plant), and are warmer than newer and/or higher-income neighborhoods, leading to elevated risk of heat-related mortality and heat illnesses as well as higher energy costs (Hsu et al., 2021; Jesdale et al., 2013; Watkins and Gerrish, 2018).
In the US, this situation is largely the legacy of historical discrimination against racial and ethnic minorities, particularly in the form of redlining, the historical practice of denying home loans or insurance to residents based on the racial composition of their neighborhood (Hoffman et al., 2020; Locke et al., 2020; Nowak et al., 2022; Wilson, 2020). Nationwide, land surface temperatures in historically redlined areas are approximately 2.6 °C warmer than in nonredlined areas (Hoffman et al., 2020). Regionally, southeastern and western cities display the greatest differences while midwestern cities display the least.
5. Conclusion
A comprehensive heat management strategy, focused on increased forest cover both within and beyond the municipal boundaries of a large U.S. metropolitan region, is recommended to significantly reduce warm season temperatures (Stone et al., 2013).
E. Tree Planting Initiatives
The United States has a long historical tradition of municipal park and street tree planting, beginning in the mid-19th century and increasing in the early to mid-20th century after the loss of millions of American elms (Ulmus americana) to Dutch elm disease (Ophiostoma spp.) (Lawrence, 2006). In 1976, the Arbor Day Foundation launched its Tree City USA program, which now includes over 3,400 member communities (Arbor Day Foundation, 2022).
Municipal tree planting initiatives (TPI) are a form of urban greening that have gained popularity both in the US and worldwide in recent decades as a means of improving urban quality of life, while also constituting one of the most effective responses to the global climate crisis through increased carbon sequestration and storage (Bastin et al., 2019; Pincetl et al., 2013; Eisenman et al., 2021). Examples include the Million Tree Initiative (e.g., Million Trees NYC, Million Trees LA, Chicago Region Trees Initiative) (Young and McPherson, 2013), and even a Trillion Tree Campaign (Trilliontreecampaign.org, n.d.).
However, uncertainties in funding and long-term stewardship surround these large-scale initiatives (Young, 2011). TPIs are often promoted by elected officials such as mayors, and thus may be vulnerable to shifting political leadership (Campbell, 2017). Furthermore, TPIs differ
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Professional Project Report: Master of City & Regional Planning Program Page 23 of 91 from traditional urban forestry activities in that while the latter have historically been the domain of the public sector alone, TPIs are commonly initiated and funded by nonprofit organizations and grassroots campaigns in partnership with municipalities (Young and McPherson, 2013). This lack of institutionalization and traditional infrastructure funding raises concerns over the feasibility of using non-public sector actors – often, untrained volunteers – to make the necessary long-term stewardship commitments (watering, pruning, mulching) that are required if newly planted trees are to survive.
The success of TPIs may also be affected by differing expectations on the part of tree planting leadership vs. the urban residents whose support is solicited; please refer to Section V.F, Equity, for details.
Not everyone is convinced in the efficacy of mass tree planting campaigns. Some researchers believe instead that promoting natural regeneration and emphasizing local/indigenous stewardship will result in stronger, more diverse forests that are better at providing the desired environmental and other benefits in the face of intensifying droughts, insects, wildfires, and logging pressure (Rosza, 2021; Rosza, 2022).
In conclusion, because the success of TPIs has rarely been measured (Danford, 2014), their ability to achieve desired outcomes over years or decades is unknown (Roman, 2014).
Furthermore, when tree-planting entities do attempt to assess outcomes, they commonly use somewhat limited metrics such as tree survival rate and percent canopy cover. Taking a largerscale, more holistic look could be informative and might include the measurement of factors related not only directly to trees and forest characteristics, but also to soils, climate/ atmosphere, built environment, tree care/maintenance, social characteristics of urban spaces, and human decisions and governance (Ordoñez et al., 2019).
F. Equity
Many studies have shown that urban tree cover is associated with factors such as income, race, ethnicity, and education. Significant positive correlations exist between poverty, minority populations, and disproportionate exposure to environmental degradation and the effects of climate change; this situation has led to the rise of the environmental justice (EJ) movement (e.g., Landry and Chakraborty, 2009).
Low-income and/or minority-dominated neighborhoods commonly have less landscaping (including trees) and fewer opportunities for outdoor recreation than more affluent neighborhoods, leading to poorer health outcomes and disproportionately high energy bills (Elmes et al., 2017; Gerrish and Watkins, 2018; Moskell and Allred, 2012; Schwarz et al., 2015; Watkins and Gerrish, 2018). One study found that in 37 US cities, high-minority, historically redlined neighborhoods contain approximately half the amount of tree canopy cover as newer housing stock with primarily white residents (23% vs. 43%) (Locke et al., 2020).
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Professional Project Report: Master of City & Regional Planning Program Page 24 of 91 Furthermore, not only do disadvantaged groups suffer greater exposure and susceptibility to unfavorable environmental conditions than wealthier segments of society, but they have less financial ability to cope with and recover from disasters and thus become even more vulnerable to climate-related disasters over time in a vicious cycle (Islam and Winkel, 2017).
One obvious solution for cities, although not a panacea, would be to prioritize tree planting in low-income neighborhoods. Counterintuitively, however, this type of policy has often failed and resulted in complaints being directed toward municipal governments in Los Angeles, New York, and other cities (Battaglia et al., 2014; Pincetl, 2010; Carmichael and McDonough, 2019). One study found that the lowest survival and growth rates of newly planted urban trees were in those planted by public housing groups (Jack-Scott et al., 2013).
In some cases, these failures have been the result of policy and funding difficulties as well as limited space available for planting in dense urban areas (Danford et al., 2014). However, another significant reason for the failure of urban tree plantings is that decisions around such programs have traditionally been made at the local governmental level in a top-down, hierarchical fashion by organizers who are overwhelmingly white and highly educated, often in contrast to the overall demographic characteristics of the cities and neighborhoods in which they work (Campbell et al., 2016).
Failure to consult affected residents about proposed changes in their neighborhood sends a message that their opinions are not valued (Moskell and Allred, 2012; Westphal, 2003). Perhaps because of this long-standing feeling of neglect in marginalized communities, many urban residents are not interested in participating in tree planting or care (Moskell and Allred, 2013), and community leaders and urban forestry professionals struggle to engage them. This could change if planners made an effort to address structural inequities in the built environment with their programs instead of focusing solely on promoting sustainability (Flocks et al., 2011).
In summary, municipal authorities must try to develop stronger, trusting relationships with underserved communities by meaningfully including those communities in decisions affecting their neighborhoods prior to project implementation. Aside from listening to local residents, further recommendations include:
• Determine what motivates the intended recipients most (e.g., environmental concerns vs. neighborhood quality of life?) and tailor the program to meet those priorities • Consider partnering with one or more organizations that already have experience facilitating an inclusive process
• Understand that even an apparently successful project may not be valued by all, and cannot transform a distressed neighborhood alone (Westphal, 2003).
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Professional Project Report: Master of City & Regional Planning Program Page 25 of 91 VI. Historical Context
Due to its geographic location and climate, the San Luis Obispo area has historically had minimal native tree cover (Seymour, 1986, p. 50). The Chumash people who occupied what is now the city of San Luis Obispo for over 10,000 years likely lived in a landscape dominated by grassland and chaparral, with relatively minimal patches of woodland containing coast live oak (Quercus agrifolia), California bay laurel (Umbellularia californica), and toyon (Heteromeles arbutifolia); riparian trees such as California sycamore (Platanus racemosa), arroyo willow (Salix lasiolepis), and cottonwoods (Populus spp.); and perhaps half a dozen other tree species. However, as a result of the planting of many thousands of non-native trees in San Luis Obispo over the past century and beyond, the area now contains far more trees (and tree species) than at any previous time in human history (Seymour, 1986, p. 50).
The era of Euroamerican settlement and urbanization in the San Luis Obispo area began 250 years ago with the establishment of Mission San Luis Obispo de Tolosa in 1772. The arrival of the missionaries saw the beginning of landscape conversion to agricultural and eventually urban uses. Up to half of the area’s native tree cover may have been lost fairly quickly, as there was a continuous need for heating and cooking fuel. Historical records also indicate that early on, logs were hauled in from elsewhere in order to continue with construction on the mission buildings, implying that lumber was in short supply locally (Carotenuti, 2006).
With the establishment of the Mission, the missionaries began to plant olive (Olea spp.), fig (Ficus carica ‘Mission’), and pear (Pyrus spp.) trees brought from Mexico as cuttings, as well as grapes (Vitis vinifera) and prickly pear cactus (likely Opuntia ficus-indica). Olive oil and wine were needed for use in religious ceremonies. The missionaries were familiar with agricultural practices in dry climates and understood the importance of water conservation (Seymour, 1986, p. 50); nevertheless, food insecurity and deprivation were never far off for the Mission’s inhabitants. Drought and insect infestations intermittently caused the failure of fruit and grain crops (Carotenuti and Olson, 2004).
In the mid-1830s the missions were secularized by the Mexican government. Despite the resulting chaos experienced by the residents, including poor treatment by corrupt bureaucrats and army soldiers who were little better than criminals, Mission San Luis Obispo never ceased being an active church. The Mission was returned to the charge of the padres in the 1840s and its buildings and grounds, although neglected, never fell into complete ruin as did those at some of the other missions (Carotenuti and Olson, 2004; Engelhardt, 1933; San Luis Obispo County Historical Society, 1972).
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Professional Project Report: Master of City & Regional Planning Program Page 26 of 91 Excerpt from Harris and Ward’s 1870 map of downtown San Luis Obispo; the Mission is seen near the bottom between Broad and Chorro, with the Mission orchard to the north. Photo by Christopher Hamma.
By the post-Civil War era, tree planting and creation of park-like landscapes had begun to capture the public’s imagination in the US, thanks in part to the design and construction of New York’s Central Park by Frederick Law Olmsted and Calvert Vaux between 1858 and 1876 (Blackmar and Rosenzweig, 2018). In San Luis Obispo, newspapers such as the San Luis Obispo (Weekly) Tribune sang the praises of urban trees in their pages and lamented the general citywide lack of them, citing their beauty, their “sanitary value” as air-purifying sources of “relief and coolness,” and their usefulness as sources of lumber, fruit, and medicinal products (e.g., eucalyptus oil) – not to mention their ability to increase the value of one’s real estate by
City of San Luis Obispo Community Forest Plan C. Hamma
Professional Project Report: Master of City & Regional Planning Program Page 27 of 91 anywhere from 20 to 100%(!) (e.g., San Luis Obispo (Weekly) Tribune, November 16, 1872, p.2; San Luis Obispo Breeze, February 18, 1898, p.2).
Breathless commentaries on the virtues of blue gum (Eucalyptus globulus) and exhortations to grow this species in large quantities to fuel an anticipated lumber boom were regularly seen in print in the 19th and early 20th centuries (e.g., San Luis Obispo (Weekly) Tribune, November 2, 1872, p. 2). Unfortunately for prospective timber barons, blue gum turned out to be a less than ideal candidate due to its tendency to split and warp while drying, and the boom fizzled.
Meanwhile, regarding fruit trees one newspaper editor opined that “In a few years hence, the orange groves of San Luis Obispo will be as celebrated as those of Los Angeles or San Bernardino” (San Luis Obispo (Weekly) Tribune, February 9, 1883, p.1).
Yet, then as now, it was clear that not everyone was in agreement when it came to urban trees.
A mid-1870s news brief stated:
The City Council at its last meeting ordered the removal of all the trees standing in Higuera Street between Morro and Osos Streets. These trees have long been a nuisance and their removal will greatly improve the appearance of the thoroughfare which they have long obstructed (San Luis Obispo (Weekly) Tribune, December 7, 1878, p.5).
Further complaints of the day included the following:
• Untrimmed tree limbs forcing people to walk into the street to avoid them (“…particularly disagreeable in wet weather” – San Luis Obispo (Daily) Tribune, November 1, 1883, p.3)
• Numerous instances of miscreants felling and girdling roadside shade trees (“...The name of the ass who authorized this public outrage is not known” – San Luis Obispo Evening Breeze, March 30, 1896, p.2)
• Merchants being showered with cottonwood debris at the corner of Higuera and Chorro Streets (“…on windy afternoons the down from the trees is blown into their places of business… They are anxious to have the trees cut down or some other means taken to dispose of the nuisance” – Daily Telegram (San Luis Obispo), June 1, 1911, p.5) • And finally, would-be olive oil tycoons experiencing recurring infestations of “scale bug, which is a sort of terrestrial abalone… Will not somebody try the experiment of spraying the trees with a solution of whale oil soap?” (San Luis Obispo (Daily) Tribune, July 14, 1883, p.3).
And, also as today, some people just couldn’t be bothered to be responsible members of the community:
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Professional Project Report: Master of City & Regional Planning Program Page 28 of 91 EDS. TRIBUNE: …It is well known that many of our citizens have been to considerable expense in the way of planting shade trees and beautifying the streets as well as their own property. Many of these are growing finely, but the young shoots or sprouts are constantly being bitten off by stock which are allowed to run at large in our streets. Who is to blame? SHADE TREE. (San Luis Obispo (Weekly) Tribune, June 8, 1872, p.2).
Fortunately for them, the owners of these free-spirited livestock appear to have arrived on scene too late to become ornaments on San Luis Obispo’s hanging tree, on Chorro Street between Islay and Leff Streets:
…Miss Ella Villa… has the word of her late grandmother that the “Hang Tree” bore its quota of “fruit.” “Grandmother told me many a time of having seen bodies swinging from that great tree when she came into town from her farm at Edna,” Miss Villa said. (Telegram-Tribune, 1941).
Over the years, many varieties of non-native trees and plants were brought to San Luis Obispo and planted: eucalyptus, acacia, hakea, pittosporum, melaleuca, leptospermum and bottle brush from Australia; geraniums, aloes, and bird-of-paradise from South Africa; loquats and crape myrtles from China; pepper trees and bougainvillea from South America; oleanders, arbutus, and jasmine from the Mediterranean; guava from Brazil; myoporum from New Zealand; deodar cedar from Asia; and cypresses and pines from Italy as well as other parts of California (Seymour, 1986, p. 51).
Regardless, for whatever reason, downtown San Luis Obispo remained tree-impoverished for decades. Historical photographs of downtown San Luis Obispo taken prior to the 1960s show an urban setting that looks utterly desolate in comparison to its current verdant state. In the words of one resident who moved to the city in 1930, “…there were almost no trees at all downtown… It was very barren and I couldn’t get over it” (Fairbanks, 1989).
However, starting in the late 1950s a beautification program led by City Councilman R.L. Graves resulted in the green downtown we are familiar with today (Carotenuti, 2006). City Engineer (later Mayor) Dave Romero organized the effort. It is worth noting that at the time, environmental reasons for planting street trees (e.g., air pollution removal, carbon sequestration) were either unknown or of relatively little importance to the public; aesthetics were the primary motivation for planting them (Bingham, 1968).
City Parks Director William Edward Flory was featured in a November 1963 Tribune article, describing his activities in planting 43 carrot wood (Cupaniopsis anacardioides) trees along Chorro Street in downtown (Middlecamp, 2021). Seventy more trees along Higuera Street between
City of San Luis Obispo Community Forest Plan C. Hamma
Professional Project Report: Master of City & Regional Planning Program Page 29 of 91 “Higuera Street then and now.” Photo dates unknown. Source: Davey Resource Group Urban Forestry Organizational Assessment, 2021.
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Professional Project Report: Master of City & Regional Planning Program Page 30 of 91 Santa Rosa and Nipomo Streets soon followed. A 1989 Telegram-Tribune article noted, “…Now, 400 carrot woods, Indian laurel figs, evergreen pears, Brisbane boxes, ornamental avocados, and holly oaks sprout from concrete sidewalks, creating canopies of shade and splashes of greenery” (Fairbanks, 1989).
In the 1963 feature, Flory stated that natives like coast live oak and California sycamore were not chosen for planting downtown because of their large size when mature, which would almost certainly result in sidewalk damage (ironically, in 1991 the City designated the California sycamore as the official City Tree). Despite this, some of the trees that were planted at that time and now dominate downtown present the same problem, as well as other concerns, due to their size, species, or other factors.
During the late 1960s and early 1970s, the segment of Monterey Street in front of the Mission was torn out and the area was converted into a car-free pedestrian square, creating today’s Mission Plaza (Clark, 1979). Beautifying the plaza with landscaping was a high priority for the City. Trees were moved from Santa Rosa Park and San Luis Coastal Unified School District property to the Plaza, including (from the latter) two old olive trees that had once been part of the Mission’s olive grove.
The City revived its Heritage Tree program in the 1980s (O’Sullivan, 1986). Currently, 16 properties within the city limits host one or more designated Heritage Trees (Andrews, N.D.).
The City defines these as trees that “played an important part in the day-to-day lives of our forefathers” and which made significant contributions, have historical value, and hold significant arboricultural interest (City of San Luis Obispo, 2022d).
Perhaps the highest-profile Heritage Tree in San Luis Obispo at present is the “Moon Tree,” a coast redwood (Sequoia sempervirens) that was planted as a sapling near Mission Plaza for the national Bicentennial Celebration in 1976, five years after having visited the moon as a seed aboard Apollo 14 (Sheeler, 2018). The planting of this tree prompted a congratulatory telegram to City officials from President Gerald Ford, who called it “a living symbol of our spectacular human and scientific achievements” (Groshong, 1987).
Other notable urban forest events in San Luis Obispo include:
• In 1912, D.J. Riley of Riley’s Department Store asked his neighbors on Mill Street if they would mind him planting trees along their block, between Pepper and Johnson. There were no objections. Those camphor trees (Cinnamomum camphora) are now 110 years old, make the block uniquely beautiful, and indeed define the Mill Street Historic District. At some point the City had to start heavily pruning the trees because truck and bus traffic was constantly knocking branches off, and there have been instances of sewer line invasion by roots, but the residents love the trees regardless (Zeuschner, 1989)
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Professional Project Report: Master of City & Regional Planning Program Page 31 of 91 • Pioneer son Warren Sinsheimer made the Tribune’s front page in 1963 for his plan to preserve the very old sycamore, olive, and eucalyptus trees at Marsh and Osos Streets while constructing the new Sinsheimer Trust Building and simultaneously repairing the dilapidated Marsh Street Bridge. The olive trees were part of the original Mission olive grove; some of them were planted in 1772 (San Luis Obispo Tribune, October 24, 1963, p.1)
• In 1980, a 210-year old Mission fig on Chorro Street between Peach and Walnut Streets fell in a windstorm. This tree had been planted by the friars in 1770 (Scott, 1980, February 8). After its demise, over 1,000 cuttings were potted by Cal Poly’s Ornamental Horticulture Department, intended for sale and planting around town (Scott, 1980, February 23)
• In 1989, the City’s Commemorative Grove was established at Laguna Lake Park. Nine commemorative trees and 38 windbreak trees were planted for the occasion (City of San Luis Obispo, 2022c)
• On November 26, 2007, the City Tree Committee approved the removal of the famous 45-year old floss silk tree (Ceiba speciosa) in front of Mission San Luis Obispo due to its roots cracking the walls of a planter attached to the mission – its second offense after a similar episode in the early 1980s (Fairbanks, 1989). Relocation was considered but was ruled out due to concerns that 18th century tiles under the tree, and perhaps other archeological artifacts, could be damaged. The tree was removed in June 2008. As with the Mission fig discussed above, it was expected that “…1,000 floss silk clones (would) be available for planting in the city by the end of summer” (San Luis Obispo Tribune staff, June 13, 2008).
• Within the past few years, some high-profile tree removals have raised controversy in town:
o In 2017, 49 trees up to 100 years old were removed at 71 Palomar Avenue to make way for a student housing complex (Schmidt, 2016); the City required 2:1 replacement for the removed trees (City of San Luis Obispo, November 13, 2017)
o Also in 2017, a large, beloved 85-year old eucalyptus (the “Big Tree”) and several other trees including a large oak were removed at San Luis Obispo High School in light of plans for new construction on the campus (Leslie, 2017). Over 1,600 protest comments were posted online in an effort to save the eucalyptus, but the tree was considered a safety hazard and had grown into the school’s main sewer line, causing blockages (Wilson, 2016; Ferreira, 2017).
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Professional Project Report: Master of City & Regional Planning Program Page 32 of 91 VII. Policy Context
The CFP is intended to align with the City of San Luis Obispo General Plan, Municipal Code, Major City Goals, and other applicable plans and policies. Selected examples are listed on the following pages.
A. General Plan Policies
Land Use Element, Sustainability Policy 9.9 - Renew the Urban Forest:
The City shall develop a long-term tree planting program to beautify the city, mitigate increased residential density, address die-off, and combat air pollution and global warming.
Land Use Element, Sustainability Program 9.10 - Urban Forest:
The City shall update the master tree plan and develop recommendations to renew and maintain the urban forest and plant more trees.
Conservation and Open Space Element, Materials Policy 5.5.2 - Promote City Materials Reuse and Recycling:
The City will manage its operations to foster reuse and recycling by:
D.) Making wood from tree removal available for mulch, milling, pulping or heating, depending on its characteristics and the volume available, while avoiding the introduction or spread of invasive, non-native species and pathogens. Selection of trees for City streets, parks and grounds will take into consideration their eventual disposal.
Conservation and Open Space Element, Natural Communities Policy 7.5.1 - Protection of Significant Trees:
Significant trees, as determined by the City Council upon the recommendation of the Tree Committee, Planning or Architectural Review Committee, are those making substantial contributions to natural habitat or to the urban landscape due to their species, size, or rarity.
Significant trees, particularly native species, shall be protected. Removal of significant trees shall be subject to the criteria and mitigation requirements in Chapter 8.6.3. Oak Woodland communities in the Greenbelt and in open space areas shall be protected.
Conservation and Open Space Element, Natural Communities Policy 7.5.3 - Heritage Tree Program:
The City will continue a program to designate and help protect “heritage trees.”
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Professional Project Report: Master of City & Regional Planning Program Page 33 of 91 Conservation and Open Space Element, Views Policy 9.1.4. - Streetscapes and Major Roadways:
The City will…
B.) Encourage the creation and maintenance median planters and widened parkway plantings.
C.) Retain mature trees in the public right-of-way.
D.) Emphasize the planting and maintenance of California Native tree species of sufficient height, spread, form and horticultural characteristics to create the desired streetscape canopy, shade, buffering from adjacent uses, and other desired streetscape characteristics, consistent with the Tree Ordinance or as recommended by the Tree Committee or as approved by the Architectural Review Commission.
Safety Element, Wildland Fire Safety Policy 3.1B:
New subdivisions shall be prohibited in areas of “Very High” wildland fire hazard as shown in Figure 2 unless part of conservation or open space acquisition program. Development of existing parcels shall require a development plan to manage fuels, maintain a buffer zone, and provide adequate fire protection to the approval of the Chief Building Official. The development plan must be consistent with Policies required by the City’s Conservation and Open Space Element.
Safety Element, Hazardous Trees Policy 8.0:
Minimize danger to people and property from trees that are weakened and susceptible to falling or limb loss during storms.
Safety Element, Hazardous Trees Program 8.1:
The City will identify, and maintain or remove, trees on City property to minimize hazards, and will work with property owners to do the same.
B. Municipal Code (2021)
Chapter 12.24 – Tree Regulations
12.24.010 – Purpose and Intent.
A. The public interest and welfare require that the city establish, adopt and maintain a comprehensive program for installing, maintaining and preserving trees within the city.
B. This chapter establishes policies, regulations and specifications necessary to govern installation, maintenance, removal and preservation of trees to beautify the city, to purify the air, to provide shade and wind protection, add environmental and economic value and to preserve trees with historic or unusual value.
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Professional Project Report: Master of City & Regional Planning Program Page 34 of 91 C. It is the policy of the city to line its streets with trees and to conduct a consistent and effective program for maintaining and preserving these trees. This policy provides for planting trees in all areas of the city and for selecting appropriate species to achieve the city’s goals. It is also the policy of the city to protect and preserve all desirable trees, wherever they are located. It shall be the duty of the director to enforce, implement and carry out this policy and the provisions of this chapter.
D. It is the policy of the city to encourage new tree planting on public and private property and to cultivate a flourishing urban forest with an emphasis on native and drought tolerant species.
E. Trees are essential to the community’s well-being and the care and planting of all trees will be done in a manner consistent with city policies and standards. (Ord. 1544 § 1 (part), 2010)
12.24.020 – Tree Committee.
A. The tree committee shall act as an advisory body to the director and the city council on all matters related to trees in San Luis Obispo.
B. The tree committee membership shall be governed by tree committee bylaws, as approved by the council. (Ord. 1589 § 1, 2013: Ord. 1544 § 1 (part), 2010)
12.24.160 – Heritage Trees.
A. The city recognizes the important role trees have played in the history and development of San Luis Obispo and recognizes that a wide variety of trees can grow in its unique and temperate climate.
B. Any healthy tree within the city limits may be proposed as a heritage tree. The city arborist and tree committee review each proposed heritage tree and, with the owner’s consent, recommend suitable candidates to the city council for official designation as heritage trees.
C. The city shall protect and maintain all designated heritage trees. Heritage trees shall be pruned according to a schedule developed and approved by the public works director. All interim maintenance shall be the responsibility of the property owner. (Ord. 1544 § 1 (part), 2010) C. 2021-2023 City Goals
Major City Goals: Climate Action, Open Space & Sustainable Transportation – Expectation #3:
The City will engage in projects and initiatives that contribute positively toward integrating best practices for urban forestry throughout the community and City landscape in order to accrue the multiple benefits that trees provide including shading and cooling, beautification, habitat, stormwater retention, and carbon sequestration.
City Goal Strategy 4.3 ‐ Preserve and enhance open space and the urban forest:
… The City is also long recognized for the past 37 years as part of the Arbor Day Foundation’s “Tree City USA” network that extends across the entire country. This Major City Goal provides an
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Professional Project Report: Master of City & Regional Planning Program Page 35 of 91 opportunity to focus renewed efforts on the City’s cherished urban forest by completing the first ever Urban Forest Master Plan, providing a comprehensive update of the City’s tree inventory and assessing overall tree canopy, implementing a contemporary tree database and tracking system, working towards the goal of planting 10,000 new trees by 2035 in partnership with ECOSLO and the community, and moving towards an integrated approach to urban forestry that accounts for street trees, park trees, open space trees, and riparian trees in a more holistic manner.
D. Climate Action Plan for Community Recovery (2020)
The 2020 Climate Action Plan for Community Recovery (CAP; City of San Luis Obispo, 2022b) sets out the City’s proposed approaches to achieving carbon neutrality by 2035, organized into six “pillars.” Each pillar has a long-term goal and foundational actions to be initiated or completed by 2023.
The goal of Pillar 6, Natural Solutions, is to “increase carbon sequestration on the San Luis Obispo Greenbelt and Urban Forest through compost application-based carbon farming activities and tree planting.” These activities are projected to be ongoing through 2035.
Natural Solutions foundational action 2.1 – “Prepare the City’s first Urban Forest Master Plan by 2021 and plant and maintain 10,000 new trees by 2035” – reads as follows:
The City will prepare its first Urban Forest Master Plan that updates the existing tree inventory and identifies future tree planting opportunities with climate-ready tree species, as well as strategies for ongoing operations and maintenance. The Urban Forest Master Plan will also include a feasibility study to propose and assess an ambitious tree planting campaign called 10 Tall: An Initiative to Plant 10,000 Trees in San Luis Obispo by 2035.
It is not presently known how close the planting of 10,000 new trees would bring the City to a target of 25% canopy cover, or when exactly that might occur.
E. Conservation Guidelines for Open Space Lands (2002)
Vegetation Management Policy LV4, Native Trees:
Preserve all native trees when feasible.
Vegetation Management Policy LV5, Tree Planting:
Plant new native trees to increase benefits to wildlife where appropriate. Use fencing to exclude livestock and damaging wildlife (e.g., deer) from newly planted areas.
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Professional Project Report: Master of City & Regional Planning Program Page 36 of 91 Fire Management Policy LV6, Vegetation Thinning:
Thin eucalyptus, pine and cypress plantations, shrub-land or woodland areas occurring along the wildland/urban interface to create a less fire-prone condition.
Fire Management Policy LV8, Controlled Fires:
Use controlled burns for vegetation or pest management, as per prescribed burn plan prescribed for the site. All affected residents will be notified prior to any prescribed burn.
Fire Management Policy LV9, Fire Safety:
Maintain adequate defensible spaces at the urban/open space interface, providing sufficient space between structures and flammable vegetation within which the fire service can mount a defense against fire.
Formulate fire preparedness/management plans for City open spaces. Employ firefighting methods which have the least impact on the natural resources represented on the site, providing the use of such methods do not put property or human life in danger.
F. Multi-Jurisdiction Local Hazard Mitigation Plan (2019) (Lead Agency: San Luis Obispo County) City of San Luis Obispo Mitigation Action SL.17 – Flood:
Description/Background/Benefits: Develop and carry out environmentally sensitive flood reduction programs.
Action Status: In progress. …review City owned property and property with drainage easements covering private properties and conduct vegetation management/removal as needed; …Assess and remove as necessary undesirable trees from creek system with tree/landscape contractors.
City of San Luis Obispo Mitigation Action SL.22 – Wildfire, Drought:
Description/Background/Benefits: Support ongoing urban forest maintenance and tree trimming programs, to include planting drought-resistant trees and plants.
Action Status: In progress. Urban Forest Services continues regular maintenance which includes pruning and dead tree removal in City Streets, Parks and other City owned properties.
City of San Luis Obispo Community Forest Plan C. Hamma
Professional Project Report: Master of City & Regional Planning Program Page 37 of 91 H. Downtown Concept Plan (2017) and Mission Plaza Concept Plan (2017) Downtown Concept Plan, Implementation Actions 71-73:
71. Work with partners on exploring funding incentives for additional streetscape improvements, such as adopting a tree or a planter (similar to the memorial bench and rack with plaque program).
72. Maintain a healthy downtown street tree canopy; seek to ensure obstruction-free sidewalks as well as proper tree health and growth capacity.
73. Include green infrastructure in public improvement projects whenever feasible.
Mission Plaza Concept Plan, Relevant Items:
15. Living Holiday Tree
20. Moon Tree Interpretive Exhibit
I. Presidential Executive Order on Strengthening the Nation’s Forests, Communities, and Local Economies (2022)
On April 22, 2022, President Biden issued an Executive Order expanding US government efforts to tackle the climate crisis, make our nation more resilient to extreme weather, and strengthen local economies (The White House, 2022). The Executive Order is intended to:
• Safeguard mature and old-growth forests on federal lands, as part of a science-based approach to reduce wildfire risk.
• Strengthen reforestation partnerships across the country to support local economies and ensure we retain forest ecosystems and sustainable supplies of forest products for years to come.
• Combat global deforestation to deliver on key COP26 commitments. • Enlist nature to address the climate crisis with comprehensive efforts to deploy naturebased solutions that reduce emissions and build resilience.
City of San Luis Obispo Community Forest Plan C. Hamma
Professional Project Report: Master of City & Regional Planning Program Page 38 of 91 VIII. New Urban Forestry Contracts (2021)
In 2021, the City awarded several new contracts as part of its effort to address deficiencies in its urban forest program. The contracts were for maintenance, a street and park tree inventory, and an organizational assessment report.
A. Maintenance
Davey Expert Tree Company and West Coast Arborists were contracted to provide maintenance services for City street and park trees. These contracts were needed in order to address several years’ worth of deferred maintenance including pruning and overall health evaluation.
B. Tree Inventory
The City awarded a contract for a new street and park tree inventory to West Coast Arborists, to replace the previous, outdated inventory. Along with the recently initiated maintenance efforts, the new inventory will provide updated information to inform future management planning, including the writing of this Community Forest Plan.
C. Urban Forestry Organizational Assessment
Davey Resource Group (DRG) was commissioned to prepare an Urban Forestry Organizational Assessment (OA) for the City Public Works Department. DRG reviewed the current Urban Forest Services program, including structure and operations, background documents, and existing policies. DRG also engaged key partners and community members and conducted an online survey to gauge community awareness and support for the urban forest.
1. Findings
The OA reported that as of 2012, the City was estimated to contain 1,050 acres of tree canopy for an overall canopy cover of 13.2%, with the highest canopy cover percentages in office and residential areas (approximately 19% each) and the lowest in business parks, at 2.5% (Nessen, 2012). The nonprofit organization American Forests recommends 25% to 35% canopy cover for dry western cities (Deeproot Green Infrastructure, 2022b).
The above estimates were derived from Light Detection and Ranging data (LIDAR [USDA Forest Service Northern Research Station, 2011]) acquired from an aircraft and therefore pertain to all trees within the city limits (i.e., including private and open space trees). However, it would not be feasible for the City to obtain a full characterization (age classes, size classes, species composition) of all of these trees through on-the-ground assessment due to presumed access difficulties on private property. Thus, in the future the City may decide to use LIDAR or other
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Professional Project Report: Master of City & Regional Planning Program Page 39 of 91 remote sensing tools again in order to generate updated estimates of percent canopy cover by land use type.
The DRG Organizational Assessment also evaluated the condition, age distribution, and species composition of the City’s street and park trees. The Assessment found that 92% of these trees are in “Good” condition or better (37%) or in “Fair” condition (55%). They exhibit a nearly ideal age distribution of many young trees and fewer old trees. Finally, species composition was found to be acceptable, with no species comprising more than 10% of the total (the most numerous species, coast live oak, was at 10%).
In the past, the City used a tree inventory management system called ArborPro to inventory trees in the public right-of-way and heritage trees on private property. In 2013-2014, this system was integrated into a larger system called Cityworks. However, after 2014 the system was rarely updated. The Organizational Assessment noted that the completion of a new tree inventory housed in a comprehensive management system would strengthen the program in several ways.
The system would allow for multiple functions including tracking, recording data, mapping, creating real-time workflows, analyzing work history, and sharing of data between Public Works divisions, with other pertinent City staff, and externally with community partners (Davey Resource Group, 2021).
2. Recommendations
The OA contained dozens of recommendations for consideration by the City in the following categories:
• Urban Forest Resource
• Operations and Programs
• Urban Forest Partners
• Organizational Structure and Staffing
DRG also made several recommendations for future City planning efforts, including additional exploration on the role of the Tree Committee, objective design standards, compensatory planting requirements resulting from development, and expanded engagement with key stakeholders and the community.
Many of the recommendations in the OA echoed comments made by CFP interviewees, and there is significant overlap between DRG’s recommendations and those presented in this document.
City of San Luis Obispo Community Forest Plan C. Hamma
Professional Project Report: Master of City & Regional Planning Program Page 40 of 91 IX. Key Findings of Stakeholder and Technical Expert Interviews In addition to and complementary to DRG’s Organizational Assessment, the following key issues were identified regarding San Luis Obispo’s urban forest program, based on stakeholder interviews, literature review, and examination of other cities’ urban forest master plans:
A. Ensure adequate funding
B. Ensure adequate staffing
C. Complete program analysis and new tree inventory; accrue and analyze data D. Strengthen maintenance practices and clear the backlog E. Increase new plantings
F. Focus on sustainability
G. Address issues unique to downtown
H. Increase outreach to officials and the public
I. Address equity issues
A. Ensure Adequate Funding
Funding was one of the two most frequently identified high-priority issues among CFP interviewees. Operating an effective urban forestry program is not inexpensive; one professional tree maintenance company has estimated that it costs $250 for one newly planted tree to make it to three years’ survival. In its Major City Goals for 2021-2023, the current City Council expressed its support by recognizing the importance of renewed efforts to protect and grow the City’s urban forest (City of San Luis Obispo, 2022a). Going forward, City residents must stand firm and ensure that the Council maintains its commitment to adequate, long-term funding if this program is to succeed and contribute meaningfully to the City’s efforts to address climate change and improve quality of life.
Creative thinking is needed on the topic of funding for the urban forest program. One example of this is the “Keys for Trees” program run by the San Luis Obispo Tourism and Business Improvement District (TBID). The TBID elected to direct 1% of revenues from its 2021-22 budget towards the City’s goal of planting 10,000 new trees by 2035 (City of San Luis Obispo, 2021; Wilson, 2021). Other funding possibilities include local business sponsorships of the City’s tree planting partners, and “gift tree” donations by individuals or businesses (City of San Luis Obispo, 2022b).
Several interviewees noted that there may be an opportunity to enhance program revenues by modifying fee/permit structures and directing these monies into a new fund dedicated specifically to the urban forestry program. Earmarking City revenues expressly for the urban forest program would be useful for budgeting purposes, allowing for the detailed tracking of
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Professional Project Report: Master of City & Regional Planning Program Page 41 of 91 income and expenditures, and it would reduce interdepartmental competition for limited general fund resources.
The City could also consider updating its tree removal application fee (currently, $157.17) and/or penalties for unauthorized removals based on alternative valuation methods for the tree(s) involved (valuation is currently based on methods established in the International Society of Arboriculture’s Guide for Plant Appraisal). The dollar amount could be modified to be based on either the value of the recoverable lumber or on the value of the ecosystem services provided by the tree when it was alive. For instance, if a project’s tree removal replacement ratio is 2:1, the replacement for one large tree would not necessarily be two smaller trees. It would be whatever number of new trees was required to eventually provide twice the value of the ecosystem services that were lost with the mature tree that was removed. Note that this would require a financial commitment on the City’s part to purchase and use specialized software (e.g., i-Tree Eco) to determine the values of said ecosystem services, or else to hire a consultant to perform that type of analysis.
Alternatively, the City could consider basing tree removal fees and/or penalties on a percentage of total tree diameter removed on a site, or allowing payment of an in-lieu fee instead. For instance, the City of Paso Robles requires that 25% of the total diameter of trees removed be replaced on site or a standard in-lieu fee be paid to fund planting on City property. As an example, removal of a 12-inch diameter tree would require replacement of three inches of diameter. At 1.5 inches minimum diameter for each replacement tree3, the result would be a requirement for two new trees.
The City may also derive funding and/or savings by continuing to work with external entities such as nonprofit organizations or other community groups, including through pursuing grant opportunities. Opportunities like this can be important in the event of City-related budgetary shortfalls. However, it is important to note that grant funding is temporary and therefore it is essential to plan ahead for the time after the grant expires.
Without stable long-term funding streams, it will be very difficult to take the necessary steps to protect and enhance San Luis Obispo’s urban forest into the future. Thus, regardless of the details of any given revenue source, the City Council must maintain its commitment to adequate funding if success is to be achieved.
B. Ensure Adequate Staffing
Aside from funding, staffing was the other issue almost unanimously identified as problematic by interviewees familiar with the City’s Urban Forest Services division (UFS). Adequate staffing is 3 Slightly larger saplings are preferred over smaller trees because they are thought to be hardier and thus have a better chance of establishment and survival (Roman et al., 2013).
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Professional Project Report: Master of City & Regional Planning Program Page 42 of 91 obviously dependent on adequate funding, but it has also been adversely affected in recent years by retirements, injuries, and the effects of the Covid-19 pandemic. As of the beginning of 2022, UFS was down to one full-time employee and one part-time employee.
Interviewee insights on this situation revolved primarily around the need to determine what level of staffing is proper, and in some cases, where City urban forestry personnel should reside within the City’s organizational chart.
1. City Employees vs. Contractors
Interviewee opinions were mixed as to whether urban forestry personnel should be City employees or contractors. The consensus was that while the program director and assistant director(s) should be City employees, field crews could consist of either one. For in-office work, an attractive option is to use interns or AmeriCorps members (including CivicSpark fellows).
The use of contractors was recommended in a City-commissioned audit evaluating the management and performance of the City’s Public Works Department (Matrix Consulting Group, April 2011). Using contractors offers certain benefits: the City is not responsible for buying and maintaining expensive equipment; City staff workload may be reduced; the City can save money over the course of time by avoiding staff injuries, liability issues, and payment of CalPERS retirement benefits; and with fewer City staff it is less likely that retirements will disrupt operations.
On the other hand, contractors require careful supervision and evaluation. One interviewee who has worked extensively with tree care contractors noted that developing and maintaining trust between a City and its contractors is crucial. Expectations regarding a contractor’s responsibilities must be clearly spelled out. For example, a company may do excellent grid or block pruning work but have little or no knowledge of long-term forest care concerns such as disease, pests, and/or the likely effects of climate change.
One interviewee opined that it is best not to sign a maintenance contract that pays a contracted company a per-tree flat rate regardless of amount of work needed; instead, they should be paid only for the work they are actually directed to do.
2. Management
Regarding management, interviewee sentiment was that the City’s urban forest program director needs to be a trained urban forester with a scientific background, planning and management experience, and excellent interpersonal and outreach skills. This person should espouse an holistic approach to urban forest management, be a strong advocate for the program, and should be effective at working with elected officials, the City’s Tree Committee, and other community leaders to achieve success. There were differing interviewee opinions as
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Professional Project Report: Master of City & Regional Planning Program Page 43 of 91 to what the title of the position should be, but feelings were unanimous that this person should be a City employee. Some respondents felt that this person does not necessarily need to be a certified arborist, although this opinion was not unanimous.
The director would oversee one to three assistant directors who are also City staff; at least one of these should be a certified arborist. One interviewee suggested that assistant manager leadership is needed in the areas of development review, code enforcement, and contractor management. These positions, although working together, may not all be in the same department. As of this writing, one decision has already been made: a new Contract Maintenance Coordinator position will be created within the Public Works Department. In addition, a job description is being created for a Citywide volunteer coordinator position, and the Community Development Department may hire an arborist to conduct development review.
The director’s role would be office-based, interacting with City staff and other stakeholders as well as overseeing program-level affairs. In contrast, the assistant director(s) would run the department’s day-to-day operations, overseeing contractors and volunteers, and responding to calls from residents as well as other situations in the field. The certified arborist would be an appropriate choice to serve as City Council and staff liaison to the Tree Committee.
3. Volunteer Labor
The City already has a long history of working with local nonprofit organizations such as the Rotary de Tolosa Club of San Luis Obispo and the Environmental Center of San Luis Obispo (ECOSLO) to hold volunteer-based tree planting events on both public and private property.
Furthermore, the San Luis Obispo area contains an as-yet largely untapped volunteer base in the form of Cal Poly and Cuesta College students, faculty, and staff. Volunteer tree planting and maintenance events can not only provide large amounts of physical labor at relatively low cost to the City and no cost to property owners, but volunteers bring with them enthusiasm and energy, thus contributing to the community’s overall sense of purpose and pride.
The use of volunteers also comes with some caveats. Volunteer events are not entirely free, as the City does incur some staff- and equipment-related costs. These include some degree of training, as volunteers do not typically possess a high level of arboricultural expertise.
Furthermore, volunteers tend to be a more reliable resource for one-time or sporadically recurring events as opposed to regular, long-term stewardship commitments. This can result in inconsistency when volunteers or property owners agree to take on long-term tree care duties but don’t follow through, which may eventually result in either additional burdens for UFS or in tree decline/death. One CFP interviewee noted that it is common for newly planted trees to die after a few years due to insufficient watering or other attention.
For this reason, ongoing outreach to property owners who request that volunteers plant a tree in their yard can be crucial to the tree’s survival. In the case of new trees that have not been
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Professional Project Report: Master of City & Regional Planning Program Page 44 of 91 adopted by a property owner, the best option may be to have dedicated City staff or contractors provide care for the first few years. Nonetheless, the interviewees largely agreed that volunteer events are both a good source of labor and an important part of amplifying public interest and buy-in.
4. Location within City Organization
Some CFP interviewees addressed the topic of where urban forestry belongs within the City’s overall organization. Currently, Urban Forest Services is housed in the Public Works Department, but as with the subject of hiring staffers vs. contractors, there is no single “right way.” Some cities place urban forestry under a parks department or a natural resources department. One interviewee, noting that there is often competition for funding both between and within municipal government departments, suggested that urban forestry could be a new, standalone City department.
One interviewee opined that public works is not the ideal location for the urban forestry program, as the expertise of public works staff is in fixed infrastructure such as utilities and hardscapes, while trees are a living, dynamic system (although, having said that, planting locations such as tree wells, road medians, and sidewalk parkways are fixed infrastructure). It was also stated that the City has seen high turnover of public works directors in recent years, creating a perceived lack of continuity in management styles.
Regardless of the City’s ultimate decisions on the organizational placement of the urban forest director and staff, it is certain that interdepartmental coordination and cooperation between Public Works, Community Development, Parks, and the Office of Sustainability will be essential in order for San Luis Obispo’s urban forest to continue to grow and thrive.
C. Complete Program Analysis and New Tree Inventory; Accrue and Analyze Data In 2021, the City awarded several new contracts for tree maintenance, an updated inventory, and an organizational assessment (see Section VIII, New Urban Forestry Contracts [2021]). As of this writing (June 2022), drafts of the organizational assessment and inventory have been completed and are under review.
The results of these efforts, in combination with data from other sources the City may choose to obtain (e.g., LIDAR), will be critical in providing a foundation for setting urban forestry targets and choosing metrics. Acquisition of current LIDAR data would also allow for a more comprehensive assessment of total carbon stored and other characteristics across all trees within the City – not just publicly owned trees, but those on private property as well.
Cities commonly use methods such as inventories and canopy cover analysis to guide urban forest planning, management, and policy efforts but fail to conduct long-term monitoring or
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Professional Project Report: Master of City & Regional Planning Program Page 45 of 91 mortality assessments, resulting in incomplete information on the effectiveness of the program (Roman, 2014). Therefore, San Luis Obispo should use the final selected metrics to monitor a variety of forest conditions, including survival (or mortality), every year. The accumulated data will allow for the annual assessment of year-over-year trends and progress toward overall goals.
This assessment, in turn, will be used to inform science-based best management practices that will protect and strengthen the City’s urban forest, thereby promoting public health and contentment.
The data gathered by the City may also be analyzed annually or every few years to determine the dollar value of the benefits supplied by the urban forest. When publicized by the City, these figures will serve as compelling evidence that protection and expansion of the urban forest is a fiscally sound, responsible goal.
1. Targets
Currently identified targets include the following:
• Plant 10,000 new urban trees in San Luis Obispo by 2035 (City of San Luis Obispo, 2022b)
o Potential sub-target: plant a certain number of new trees per year o Potential sub-target: plant a certain number of new trees per given geographic area (hectare, square kilometer/mile, neighborhood, special-status zone [e.g., low-income], other)
• Reduce annual greenhouse gas (GHG) emissions by 1,490 metric tons of carbon dioxide equivalent (MTCO2E) in 2035 (City of San Luis Obispo, 2022b) Potential urban forest targets may include:
• Attain a specified percent tree canopy cover for the City as a whole, or by neighborhood (includes privately owned trees)
• Attain 100% City tree well stocking
• Attain 100% replacement of other City trees that were previously removed (e.g., in parks)
• Prune/mulch a specified number of trees per year
• Sequester a specified annual rate of MTCO2E per year
• Attain a specified total carbon storage amount (MTCO2E) in the City’s trees • Designate primary and secondary species of City-owned trees for each City block, street segment, and/or neighborhood
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Professional Project Report: Master of City & Regional Planning Program Page 46 of 91 • Produce neighborhood-level tree maps and make them publicly available online, similar to the City of Santa Monica
• Attain a high percentage of “climate-ready” City-owned trees per geographic area.
These trees belong to species that are believed to be most resilient to the projected effects of climate change in central California, both direct (increased heat, drought, air pollution, extreme weather events) and indirect (increased attack by disease and pests). • Achieve a certain dollar value(s) in specified ecosystem services.
2. Metrics
Potential urban forest metrics, measured by neighborhood and/or on a citywide basis, could include the following examples. These metrics could be taken as one-time “snapshots” or, more usefully, taken repeatedly over time in order to discern trends. Some of these would necessarily be estimates:
• % tree well stocking
• % potential park tree stocking
• % survival of newly planted trees at x years (1, 3, 5, 10, 20, 30…) • % canopy cover
• species composition/diversity
• annual carbon sequestration and total storage
• % public trees vs. total trees
• % private vs. public tree ownership
• impervious surface cover (this metric is negatively correlated with urban tree cover).
3. Data Analysis
The City may choose either to analyze its urban forest data in-house or to hire a vendor to do so.
A variety of private firms specialize in forest management analysis software and/or offer consulting services. These companies commonly perform analytical studies for cities and other agencies. One such firm that was mentioned as well-regarded by at least two CFP interviewees is PlanIt Geo (PlanIt Geo, 2021).
Assuming that data collection will be ongoing and that the City’s inventory of street and park trees (and perhaps the CFP itself) will be updated every few years, it is expected that analysis of the urban forest data will lead to new insights and new initiatives over time. Evaluation of the data may illuminate forest health- or growth-related trends that require action. For instance,
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Because of the likelihood that adjustments will be needed over time, it will be important for the City to retain flexibility by taking an adaptive management-based approach.
A Note on Canopy Cover: Percent canopy cover is a commonly used metric that measures the percentage of ground covered by a vertical projection of the tree canopy (Egan, 2010). Currently in the United States, there is a trend towards urban canopy cover increasing in multifamily residential and office/business zones while decreasing in single-family residential (SFR) zones. In California, this effect may be exacerbated by recent legislation promoting the construction of accessory dwelling units (ADUs) in SFR zones as a strategy to address the State’s housing crisis.
The use of canopy cover as an urban forestry metric has come under some criticism in recent years (Kenney et al., 2011), including from some CFP interviewees who believe it is not the most useful measure for a City tree program. This is in part because it is difficult for a government agency to significantly influence tree cover on a large (e.g., citywide) scale because most trees are located on private property. Instead, CFP interviewees stated, it is more important to quantify what the City’s existing trees are doing in terms of providing benefits, and to translate that into dollar amounts that can be highlighted in outreach efforts.
D. Strengthen Maintenance Practices and Clear the Backlog San Luis Obispo currently faces some of the same urban forestry concerns that have been experienced by cities nationwide: declining age and species diversity, the effects of climate change (drought-induced water stress, increased susceptibility to pest and disease attack, damage from extreme weather events), and inadequate funding that affects staffing levels and has resulted in years’ worth of deferred maintenance.
While planting new trees (see Section IX.E, Increase New Plantings) is an important and necessary part of urban forest management as well as the City’s climate action strategy, it is at least as important to properly care for existing trees to maximize their health, longevity, and therefore, benefits provided. Some CFP interviewees noted that the funding and staffing issues are of particular concern for this reason; if not given timely attention, many existing but distressed trees that could otherwise be saved might die. Additionally, regardless of the cause of a tree’s death, the City should consider its end-of-life use by planning for sustainable uses of the lumber (see Section IX.F.2, Lifecycle Perspective).
Under current Public Works management practices, City-owned trees within San Luis Obispo are split into nine pruning zones and intended to be pruned on a block-by-block basis (City of San Luis Obispo, 2022g). Going forward, this maintenance will be the responsibility of contractor crews; in 2021, the City signed a $150,000 pruning contract with Davey Tree Expert Company. A
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The concept of “pruning cycles” has commonly been used in urban forestry to budget for annual maintenance, but several interviewees familiar with the topic felt this approach is less than ideal due to large variations in the needs of tree species as well as individual trees.
It may instead be possible to have the contractor implement multiple, concurrent pruning cycles. This would further reduce pressure on overtaxed City staff while allowing for more a tailored approach to maintenance and thus forest health. However, if the decision is made to stay with one overall pruning cycle, five years can be considered adequate.
At least one respondent also noted that it can be valuable for City staff to do annual ad hoc “windshield surveys” of public trees in order to detect existing or incipient problems in a timely manner.
E. Increase New Plantings
Agreement was unanimous among CFP interviewees that more planting of urban trees is warranted in order to counteract ongoing urban tree loss and to ensure the presence of a future urban forest that maximizes social, economic, and ecosystem benefits. The undesirable effects of the trend towards loss of urban trees may be more pronounced in cities that have little natural tree cover to begin with, like San Luis Obispo.
City streetscapes, parks, creek corridors, open space areas, and private property are all appropriate locations in which to consider the planting of additional trees. In the past few years the City has collaborated with local community groups, including the Rotary de Tolosa Club and ECOSLO, to plant several hundred new trees in such locations. Building on these efforts, the City’s 2020 Climate Action Plan for Community Recovery (CAP; City of San Luis Obispo, 2022b) called for the rejuvenation and expansion of the City’s urban forest through the planting of 10,000 new trees by 2035. Subsequently, the City Council incorporated this proposal into the City’s 2021-2023 Major City Goal for Climate Action, Open Space & Sustainable Transportation (City of San Luis Obispo, 2022a).
To help get the process started, local stakeholders created the 10 Tall tree planting initiative. 10 Tall is a City campaign that is nested in the 2020 CAP, Pillar Six: Natural Solutions (City of San Luis Obispo, 2022b). It is anticipated that the majority of the 10,000 trees proposed for planting will be San Luis Obispo native species that will be planted in City open space areas and riparian corridors. 10 Tall is expected to be a priority area of focus during the City’s CAP 2022 Update.
The City may also want to consider modifying its engineering standards to increase the number of trees required in new development, including along sidewalks and in parking lots, as
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Community engagement will also be an important part of the 10 Tall program. As of this writing (June 2022), the group is working with computer science students at Cal Poly to create a website where any community member – whether an individual, household, or organization – will be able to register trees it has planted within the City limits. The database linked to the website will be accessible to the City and its tree care partners to facilitate monitoring of progress toward the 10,000 tree goal as well as the recording of urban forest metrics (e.g., diversity of species planted or survival at various time points).
F. Focus on Sustainability
As awareness of global climate change has entered the general consciousness in recent years and calls for action have become more urgent, the importance of urban forestry has begun to receive more attention from the public. Tree planting has increasingly come to the fore as a “low-hanging fruit” climate change solution (Mandel, 2021). Planting sites are numerous, trees and volunteer labor are readily available, and there is nothing particularly complicated about the procedure. The number of tree planting initiatives sponsored by government agencies, corporations, and other entities has dramatically increased since the beginning of the 21st century.
However, the issue is more complicated than it may seem. Putting trees in the ground is just one small part of sustainable urban forest management. Furthermore, opportunities for missteps abound in urban forestry – for instance, planting in the wrong location or planting species that may not be resilient to the effects of climate change. Thus, comprehensive planning is needed in order to avoid outcomes that diminish or negate the desired environmental, social, and economic benefits that motivated planting in the first place.
1. Right Tree, Right Place
The “right tree, right place” concept ties together various aspects of sustainability that are discussed on the next several pages.
A thriving, productive urban forest contains a mix of species and individual trees that are appropriate for the physical location and environmental conditions in which they were planted.
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Thus, the determination of what constitutes “right tree, right place” should be made for each individual combination of planting site and tree to maximize health, productivity, and longevity.
Failure to do this may result in reduced tree vigor, premature illness, and death, or premature tree removal due to unwanted impacts on utilities or other infrastructure, not to mention reduced or unrealized urban forest benefits.
Broadly speaking, sidewalk parkways and road medians are generally more suitable for smaller, less messy trees, while larger species that drop more biomass but store more carbon and create better wildlife habitat are more appropriate for use in parks, riparian corridors, or open space areas. While urban foresters commonly favor large-growing tree species for maximization of ecosystem services (USDA Forest Service, 2004), city residents tend to prefer smaller, fruiting or flowering trees for their aesthetic benefits (Eisenman et al., 2021).
One example of a species that is not particularly well-suited for San Luis Obispo is the coast redwood (Sequoia sempervirens). The city’s climate is very dissimilar to the fog-shrouded, damp coastal environment where redwood grows naturally. While some local redwoods seem reasonably healthy, many others are in poor condition, unable to thrive in our present climate and presumably even less so in the future considering the predicted effects of climate change.
As another example, the huge, beautiful Indian laurel figs (Ficus microcarpa) in downtown San Luis Obispo, while widely admired, have outgrown their environment. Cramped city sidewalks are no longer an optimal location for these trees at their present size.
On the other hand palms, although they do not offer much in the way of cooling or carbon sequestration, provide some degree of wildlife habitat and are appropriate for planting in areas of limited space. Furthermore, palms are culturally important in southern California.
2. Lifecycle Perspective
Upon removal, urban trees have traditionally been considered to have little value and chipped, burned, cut into firewood, or buried in a landfill (Nowak et al., 2019). However, these practices either quickly or eventually allow the carbon stored in the wood to escape to the atmosphere.
Furthermore, a potentially useful job-producing and income-producing resource – to the tune of 46 million tons of wood per year, worth anywhere from $89 million to $786 million – is largely
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Thus, one way in which the CFP can contribute to sustainability is by promoting adoption of a lifecycle perspective toward urban trees – that is, acknowledging that each tree serves one or more distinct purposes from planting through removal and subsequent use of the lumber and other organic debris. This concept requires a philosophical shift from “planting trees” to “growing trees” (Mandel, 2021); that is, a change of focus to long-term maintenance practices that encourage a lifetime of arboreal health. Failure to address these needs (i.e., neglect) often results in poor tree health and low survival rates.
Interest in alternative uses of urban waste lumber has been rising for a number of years now.
The benefits of this approach include reduced wood waste in landfills, increased urban jobs, reduced need for harvesting rural forests, and potentially avoided carbon emissions and enhanced municipal forest management revenue (Nowak et al., 2019). The lumber can be used in a wide variety of ways, including as feedstock for engineered woods, landscape mulch, soil conditioner, animal bedding, compost additive, sewage sludge bulking medium, and boiler fuel (CalRecycle, 2022c).
However, some CFP interviewees also expressed the desire to see waste lumber used in the creation of boutique furniture, public art, or infrastructure such as fencing or benches, which would store the carbon within the wood indefinitely and could be installed throughout the city with educational signage around sustainability. Local company Pacific Coast Lumber was featured in a 2016 news story using urban lumber to create just such products, building handcrafted cabins, sheds, benches, tables, chairs, and flooring among other products from dead and diseased Monterey pines that were removed from Cambria’s pine forest (Buffalo, 2016). In order for this idea to work long-term in a city setting, urban forest managers will need to consider lumber quality in addition to the various other desired benefits from trees under their care when choosing trees to plant.
In a related project, in 2020 the local nonprofit ECOSLO received a CAL FIRE Urban and Community Forestry grant for a program called “Full Circle: A Sustainable Approach to Urban Lumber in San Luis Obispo” (CAL FIRE, 2020). This multifaceted project would divert 600 urban logs from the waste stream over three years, plant 240 new trees, and create a new college and vocational curriculum, donating wood to and working with local schools to teach students about the sustainable processing and use of urban wood. ECOSLO contracted with local business Deadwood Revival Design for program implementation. As of this writing, the Full Circle program is in progress.
Urban lumber can also be used in cogeneration, the creation of bioenergy (electricity, heat, fuel) from waste biomass. Although some carbon dioxide is generated and escapes to the atmosphere in this process, the net effect is reduced GHG emissions and air pollution (including
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The Hitachi Zosen-INOVA dry anaerobic digester near the San Luis Obispo airport reduces greenhouse gas emissions by diverting green waste and food waste from the Cold Canyon landfill and recycling them into compost, liquid fertilizer, and electricity (Hitachi Zosen Inova AG, 2021). However, the facility cannot process large woody debris; SLO County does not currently have any facility that can do so.
3. Climate Readiness
Climate readiness refers to the resilience of an urban forest to environmental stressors resulting from the effects of global climate change (McPherson et al., 2018). Climate change has been predicted to inflict increasing heat, drought, wildfire, and extreme weather events on California in the coming years and decades, while also increasing exposure to attack by current or emerging insect pests and pathogens. Furthermore, these effects may be exacerbated in cities due to the urban heat island effect, air and water pollution, poor soils, and accidental or intentional damage (vandalism).
Lack of irrigation water may also become cause for concern. As with many other cities, San Luis Obispo contains numerous examples of ornamental trees that originated in wetter climates and require substantial irrigation in order to thrive. These varieties are not considered adaptable to the projected, increasingly harsh environmental conditions accompanying climate change and therefore will likely experience increasing decline and death in the coming years, whether directly from climatic conditions or from property owners reducing or discontinuing irrigation (on the other hand, water conservation measures and recycled water are still largely untapped resources whose use may be expanded). Drought-weakened trees will also increasingly comprise a public safety hazard, with associated financial costs. For all these reasons, research to identify and test the resilience of potential new urban tree species is urgently needed to protect the long-term stability of urban forests (McPherson and Berry, 2015).
In California, researchers with the University of California, UC Davis, and the USDA Forest Service are conducting a study on this subject. The Climate Ready Trees project aims to identify the suitability of underutilized but promising tree species for urban planting in the context of climate change pressures (McPherson et al., 2018). Dozens of trees have been planted for evaluation in the Sacramento area and throughout southern California. Although growth and survival monitoring is ongoing, initial observations from southern California indicate that some species native to hot, dry landscapes are performing better in inland locations than in coastal locales, while others are tolerant of coastal conditions but require frequent pruning for optimal
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Cal Poly San Luis Obispo’s Urban Forest Ecosystem Institute (UFEI; Urban Forest Ecosystems Institute, n.d. [a]), home of the SelecTree system, is also involved in the effort to find and evaluate climate-ready urban trees.
4. Diversity
Diversity is a core ecological concept that refers to the variety and relative abundance of a species (Magurran, 1988). High species diversity, age diversity, and geographic distribution are believed to lead to greater population resilience because although decimating factors (e.g., pests and disease, natural disasters, exploitation by humans) may act upon specific portions of a diverse population, a single event is unlikely to eliminate the entire population of that species.
In contrast, monocultures or other areas of limited diversity are theoretically at higher risk of being eliminated by a single decimating event. High tree species diversity can also enhance benefits including aesthetics and wildlife habitat.
Urban forests in the US typically have far higher species diversity than adjacent native forests or woodlands (Robertson and Mason, 2016). In California, overall urban tree species diversity is considered adequate, but 39 of 49 inventoried communities were identified as being overreliant on a single species of street tree (typically London plane, sweetgum [liquidambar], Chinese pistache, velvet ash, or Callery pear) (McPherson et al., 2016). This is in part because commercial tree growers naturally meet demand by focusing on varieties that are easiest to grow and sell most readily to high-volume buyers. When one of these trees dies or is removed, it may be wise to consider replacing it with a different, more appropriate species. One suggested best practice for urban forestry is to aim for a forest composition of no more than 10% of any single tree species, no more than 20% of species in any tree genus, and no more than 30% of species in any tree family (Santamour, 2004).
San Luis Obispo does contain some individual trees of uncommon species that were planted long ago but for which replacements from the same species are no longer available, contributing further to concerns about declining species diversity in the city over time. City staff anticipates that the 2021-2022 street and park tree inventory conducted by West Coast Arborists (under review as of this writing) will be helpful for assessment of urban tree diversity in the city, even though it will not include trees on private property.
5. Pests and Disease
With each passing decade, the number of non-native, invasive pests and diseases in California increases through commercial activity or other means of transportation from distant areas.
When these organisms establish self-sustaining populations, the result can be tens or hundreds
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San Luis Obispo County has been living with one such invasion since at least the early 1990s. The disease pitch canker, caused by the fungus Fusarium circinatum, was inadvertently introduced to California (Santa Cruz County) in 1986. This pathogen has caused enormous die-off of pines in California, including the widely planted Monterey pine (Pinus radiata). The poor condition and high fire hazard of Cambria’s native stand of Monterey pine, where pitch canker was first detected in 1994, is in part due to this disease. Because pitch canker has also caused significant morbidity and mortality in ornamental pines in San Luis Obispo, it is specifically called out in the City General Plan’s Safety Element, Chapter 8: Hazardous Trees.
It is possible that this unfortunate situation could be repeated in other tree species in San Luis Obispo County before long. Sudden oak death (SOD), caused by the fungus-like microbe Phytophthora ramorum, is estimated to have killed over one million trees, mostly oaks and tanoaks, in coastal California since its discovery in the mid-1990s (UC Riverside CISR, 2022). SOD also infects dozens of other native plant and tree species, and it is currently documented in southern Monterey County – just a few miles from the San Luis Obispo County line. Research indicates that the strongest predictor of SOD is the presence of California bay laurel (Umbellularia californica; California Oak Mortality Task Force, 2021) – a native tree that grows in abundance in San Luis Obispo’s riparian and open space areas.
The invasive shot hole borers (ISHB), two closely related species of tiny wood-boring beetles from Vietnam and Taiwan, were first detected in large numbers in southern California between 2012 and 2014. These beetles attack 58 tree species, killing the trees in two ways: by girdling (tunneling through living tissues), and through the introduction of fungi of the genus Fusarium which eventually clog the tree’s vascular tissues, preventing the movement of water and nutrients. In 2017, ISHB was predicted to have the potential to kill 27 million trees in southern California (Eskalen and Lynch, 2017). As of this writing, exactly one ISHB specimen has been found in San Luis Obispo County, in 2016. The County Agricultural Commissioner’s Office is conducting limited monitoring to watch for this pest.
In each of these cases and others of concern not discussed here (e.g., goldspotted oak borer – Agrilus auroguttatus), widespread establishment of the pathogenic organism would be a serious threat to anywhere from one to dozens of native and urban trees species in San Luis Obispo County. For this reason, the CFP must address the City’s response to invasive species affecting the City’s urban forest. In addition, some types of trees may themselves be considered invasive species, e.g., tree of heaven (Ailanthus altissima), black locust (Robinia pseudoacacia), Peruvian pepper (Schinus molle), Canary Island date palm (Phoenix canariensis), and certain Acacia and Eucalyptus species.
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Professional Project Report: Master of City & Regional Planning Program Page 55 of 91 Prevention and monitoring are essential; the City must work with partners including San Luis Obispo County, CalFire, Cal Poly, PG&E and others to keep up with the latest information and best practices. As regards prevention, it was noted previously that one factor strengthening the urban forest is species diversity. In reforesting the City’s open space and creek areas as part of the 10 Tall campaign, it is natural to focus on planting San Luis Obispo’s native riparian tree species (sycamores, cottonwoods, willows, maples). However, consideration must be given to the susceptibility of these species to each invasive pest of concern, to the extent possible.
For instance, the experience with ISHB in southern California has shown that the riparian tree species listed above seem to be these insects’ most highly preferred hosts. Thus, in light of the potential threat to San Luis Obispo County, it may be prudent to consider reducing the proportions of those species planted in the City’s open spaces and creeks, replacing them with less-affected ISHB host species such as coast live oak (Quercus agrifolia), or with species like California black walnut (Juglans californica) that have not been identified as hosts of ISHB.
Upon detection of a novel pest, a rapid, IPM (integrated pest management)-based response will be required. The basic steps include quarantine, cultural practices including tree removal where indicated, and use of insecticides and biocontrols (as available and deemed necessary). Thus, the City should have funds available to respond to fast-breaking situations using an “early detection, rapid response” mantra.
6. Municipal Tree Lists
A municipal tree list is a compilation of city-approved tree varieties that is maintained by some, though not all, cities. Examples of factors that may go into a municipal tree list include whether a given species has a propensity for disrupting sidewalks and utilities, is a nuisance due to dropping copious biomass or releasing excessive pollen, is compatible with local climate and soils, and is aesthetically suitable for its intended location (City of Lodi, no date). In some cases, these lists have been perceived as limiting and drawn complaints from the public. Given the already alarming effects of climate change, Californian cities with tree lists (including San Luis Obispo) will need to make some decisions around updating their lists for the future.
The City’s current Street Trees Master List (City of San Luis Obispo, 2018) contains 68 species or cultivars that are approved for planting in the City. The San Luis Obispo City Arborist has the authority to approve planting of additional, non-listed species on a case-by-case basis. The City Tree Committee may work with City staff and partners to update the tree list as often as once a year in order to remove less-than-desirable trees (for example, those that require excessive amounts of water) and replace them with climate-ready varieties. On the other hand, the City may also consider other options including eliminating the tree list altogether (some cities do not have one), creating multiple lists (one for streets, one for parks, one for open space, etc.), or
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Ideally, decisions about the Street Trees Master List will be informed by the latest research on climate-resilient trees, such as that occurring at UFEI. However, even when or if such species are found, the desired trees may not be commercially available. CFP interviewees identified two California-based growers, Devil Mountain Nursery and San Marcos Growers, who have expressed interest in experimenting with growing new species of climate-ready trees for their customers.
Thus, identification of what constitutes “right tree, right place” in 21st century San Luis Obispo is work in progress. Regardless, it can no longer be considered appropriate to simply choose urban trees based on cost alone or on whatever is available in the greatest quantities, without taking into account resilience to changing environmental factors.
7. Tree Committee
The City’s Tree Committee is an advisory body that makes recommendations to the City Council, staff, and Planning Commission on tree policies and regulations (City of San Luis Obispo, 2022f).
The Tree Committee consists of one representative of the City Parks and Recreation Commission, one representative of the Architectural Review Commission, and five members from the general public – one of whom must be a horticultural expert.
The Tree Committee reviews development proposals, hears appeals of tree removal applications that were denied by the City Arborist, and makes recommendations on heritage tree and “significant tree” designations as defined in the City Municipal Code and the General Plan Conservation and Open Space Element. As noted previously, the Tree Committee may also assist in updating the Street Trees Master List in cooperation with City staff and partners.
There are currently some uncertainties surrounding the Tree Committee. The following points/opinions regarding the Tree Committee were raised in the Davey Urban Forestry Organizational Assessment (Davey Resource Group, 2021, p. 58):
• The roles, responsibilities, and authority of the Tree Committee are ambiguous • The Tree Committee is housed within the Public Works Department yet spends the majority of deliberations on topics relating to private trees • The community is undergoing a significant amount of infill development, partially related to an increased demand for housing, commercial sites, and the recent state Housing Mandate. Increasingly, the Tree Committee is being asked to review these development plans
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• Currently, neither the Tree Committee nor the City Arborist serve as a liaison/support for the Architectural Review Commission, yet this Commission reviews projects that involve consideration for tree preservation and removal permits • The Tree Committee has a limited advocacy role for urban forestry budgeting through an annual report to the City Council that includes desired improvements.
Furthermore, CFP interviewees offered the following observations/opinions about the Tree Committee:
• Members of the Tree Committee want decision-making authority regarding development proposals, but there is no consensus on the topic among interested parties
• Cases have arisen in which the Tree Committee requested more than one hearing on a development-related tree issue, leading to conflict because of California Permit Streamlining Act requirements. This piece of legislation limits hearings on development projects to a total of five for any given issue, and City staff believe that two of those slots should always be reserved for City Council deliberations. This may not be possible if the Tree Committee, Planning Commission, or other applicable advisory bodies hold multiple hearings on a project
• Some CFP commenters felt that the City has a surplus of advisory bodies as it is, and that the Tree Committee could be replaced by one City staffer plus one member of the public who has expertise in arboriculture.
If the City was to move forward with replacing or modifying the duties of the Tree Committee, it would be appropriate to consider whether (and if so, how) this would affect the ability of interested members of the public to observe and provide input into tree-related City actions.
8. Soil and Infiltration Enhancement
Street trees typically exist in harsh urban environments with poor soil conditions. Urbanization results in the conversion of natural land cover to impervious surfaces, changing natural drainage characteristics and inhibiting infiltration of water, gases, and nutrients into the soil.
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Professional Project Report: Master of City & Regional Planning Program Page 58 of 91 Furthermore, urban trees commonly suffer from other challenging growth conditions including lack of growing space, soil compaction, high salinity, and/or unfavorable pH, and they can be damaged by pollution and physical interference from infrastructure. These conditions can stunt trees and plants, significantly limiting their health and lifespan (Lawrence et al., 2012).
Compost Procurement under SB 1383: California’s Short-Lived Climate Pollutant Reduction law (SB 1383) establishes methane reduction targets through diversion of organic waste that would otherwise go into the landfill (CalRecycle, 2022a). The law requires recycling of food waste and addresses hunger through the recovery of edible food from the waste stream. Under SB 1383, counties and cities are required to procure a certain tonnage of compost each year for their own use or for donation to the community. The City of San Luis Obispo’s compost procurement target for 2022 through 2026 is 3,685 tons per year (CalRecycle, 2022b). Because this amount of compost exceeds current known uses for it, a potential exists for the surplus to be used in City tree planting and care, as well as in application to City open space rangeland (carbon farming).
Soil- and Infiltration-Enhancing Technologies: In recent years a variety of new soil-enhancement technologies have been developed for the dual applications of stormwater infiltration/water quality improvement and urban tree growth enhancement. These products are designed to improve infiltration and remove suspended solids and other soluble pollutants while facilitating the growth of larger trees than would otherwise be possible in confined urban settings, without damaging sidewalks, streets, or utilities.
One of these solutions is engineered soils, which consist of specific, proprietary blends of gravel, sand, silt, clay, and organic matter. By improving soil structure and chemistry, engineered soils can enhance tree and landscaping root growth and therefore overall health. This can be especially important in physically constrained planting sites such as small tree wells or planters.
However, this type of product must be used with carefully chosen tree species due to its sometimes low nutrient content.
One CFP interviewee regarded engineered soils as the most practical and cost-effective soil technology for a city to use, although they are not inexpensive. For example, approximately 11 yd3 of Cornell engineered soil (CU-Structural Soil®; Denig, 2015) is recommended for the planting of a single street tree. At a typical price of $40 per yd3(range = ~$35 to $75/yd3), this comes out to $440 per tree.
Another soil-enhancing product is soil cells such as the Silva Cell (Deeproot Green Infrastructure, 2022a). These “modular suspended pavement systems” consist of crate-like structures, posts, panels, geotextile fabric, and mesh that are assembled in excavated trenches where trees will be planted and backfilled with planting soil.
Soil cells work well (they are the “gold standard” according to one interviewee), although their cost – $14 to $18/ft3installed, or approximately 10 times more expensive than the Cornell soil
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On the other hand, their proven ability to enhance long-term tree growth and health means that these products might be suited for limited use in challenging, streetside planting areas such as along Monterey, Higuera, and Marsh Streets in San Luis Obispo. Private commercial or residential development can also benefit from the use of soil cells; the City might consider requiring soil cell installation as a condition of new development under some circumstances.
Additional products in the same vein that were mentioned by CFP interviewees included waterabsorbing polymers (hydrogels) added to the soil; rubber sidewalks (Terrecon, Inc., 2014), which received mixed reviews; suspended sidewalks; and pervious (permeable) concrete or other hardscape surfaces. A study conducted in Australia found that permeable pavement increased soil moisture in drier sandy soil but decreased moisture in wetter clay soils, with the effect on soil moisture fluctuating depending on both soil type and depth of the aggregate base layer under the pavers (Mullaney, 2015). Under some of the experimental conditions, tree diameter growth was up to 65% greater with permeable pavement than with the control (regular asphalt pavement).
9. Safety
The San Luis Obispo City General Plan’s Safety Element (last revision 12/9/2014) identifies fire, flooding, and hazardous trees, among other issues, as threats to public safety. The proximity of urban development to natural (non-urbanized), topographically varied landscapes in combination with the effects of climate change increases the potential for injury, death, and property destruction due to natural disasters. As of this writing (June 2022), the Safety Element is being updated.
The City of San Luis Obispo was a participant in the 2019 Multi-Jurisdiction Local Hazard Mitigation Plan (LHMP) spearheaded by San Luis Obispo County (County of San Luis Obispo, 2019). The LHMP relies on risk and vulnerability assessments to craft goals, objectives, and actions that provide “practical, meaningful, attainable and cost-effective mitigation solutions to reduce vulnerability to the identified hazards,” thereby reducing human and financial losses. The LHMP evaluates 16 potential hazards facing the county and its communities, identifying tree mortality resulting from drought stress and pathogen attack as a significant hazard. Other treerelated hazards include adverse weather and wildfire.
Wildland Fire: Homes and other buildings throughout the city are located in close proximity to, or interspersed with, hillslopes containing stands of native trees and brush. This zone of mixed land cover is known as the wildland-urban interface (WUI). The past two decades of increasingly severe and uncontrollable fires in the western US have shown that the physical effects of climate change on wildfire behavior (e.g., higher wind speeds, lower relative humidity and fuel moisture, potential for large areas of drought- or pest/disease-killed vegetation) have now, in many instances, intensified beyond the point at which fire suppression efforts are effective let
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Flooding: Much of the city’s urban development is located near the city’s creeks, within or in proximity to 100-year and 500-year flood zones. Flooding can be caused by rocks, trees, and other debris falling into waterways and blocking culverts and creek channels. This effect may be exacerbated after a wildfire, particularly in steeper watershed areas, as the lack of vegetation and eventual decay of fire-killed roots mean that the soil is more vulnerable to erosion. Other effects of flooding can include inundation of structures, impact damage from flood flow and debris, crop destruction, and release of hazardous materials including untreated sewage.
Hazardous Trees: Trees that threaten public safety may result from a variety of situations including poor environmental conditions or maintenance, pests and disease, or routine senescence and death. The City must continue to identify and monitor hazard zones, evaluate the potential for emergencies, and plan for site access and other responses.
10. Water Conservation
Given the increasing unreliability of winter rains in central California, water use is necessarily an important part of the conversation around San Luis Obispo’s urban forest. New policies, practices, and technologies – as well as increased reliance on existing ones – are needed going forward.
Substantial and as yet unrealized water savings are possible in California through more stringent water conservation, recycling, and stormwater capture efforts (Gleick et al., 2014). The City of San Luis Obispo currently uses recycled water (indicated by purple signs and piping) for various non-potable uses including irrigation of street and park trees (City of San Luis Obispo, 2022e).
While a detailed examination of water-saving methods is outside the scope of this plan, irrigation practices bear brief discussion here.
The City currently uses sprinkler, drip, and manual irrigation to water public landscaping, including turf and trees. In many parks and some street tree locations, as well as in new development, the City is using or requiring use of recycled water. Minimization of turf and conversion of sprinkler irrigation to drip should be a high priority for the City. Newly planted trees planted in streetscapes, medians, parks, and other locations in the public right-of-way can be located so as to take advantage of existing irrigation, but in some cases the City may choose to install temporary or permanent drip irrigation to serve new plantings. If the City decides to try any of the technologies described in Section IX.F.8, Soil and Infiltration Enhancement, drip irrigation could be incorporated into the design.
City of San Luis Obispo Community Forest Plan C. Hamma
Professional Project Report: Master of City & Regional Planning Program Page 61 of 91 Having said all this, however, the City may achieve the same desired result (healthy, wellwatered young trees) by using a time-honored, water-wise irrigation method – placement of a small, porous reservoir (“olla”) in the ground near each tree. These may be ceramic pots, or even perforated plastic jugs. The neck of the olla extends above the ground surface for quick, easy filling with water. Through soil moisture tension, the reservoir slowly releases water into the soil when the ground is dry but retains water when the ground is wet. Water loss from runoff and evaporation is minimal to none. After the tree has established, the olla can be removed and used elsewhere.
G. Address Issues Unique to Downtown
Downtown San Luis Obispo is a “special” place that is “the heart of (the) community” (City of San Luis Obispo, September 2017). Special events held in Mission Plaza and City parks, the weekly Downtown Farmer’s Market, and everyday shopping, dining, and entertainment attract many thousands of people year-round. For decades now, downtown’s lush tree canopy has been an important part of the ambience that drives and nurtures such activities.
1. Downtown Concept Plan and Mission Plaza Concept Plan By 2014, it was clear that American cities’ central business districts were suffering from the dual onslaughts of suburban big-box retail centers and expanding online commerce. That year, San Luis Obispo City leaders, staff, and residents felt strongly enough about protecting downtown San Luis Obispo’s vitality and setting forth a vision for this space that both the Downtown Concept Plan (DCP) and the Mission Plaza Concept Plan (MPCP) were updated following the City’s General Plan Land Use Element update.
The DCP (2017) is intended to guide both public and private actions and investment in downtown over the next 25 years, while the MPCP (2017) takes a close look at the plaza’s condition, uses and policies, as well as impacts on neighboring properties and the San Luis Obispo Creek corridor, opportunities for plaza expansion, and more.
The DCP specifically recognizes downtown’s urban forest in its Implementation Actions:
71. Work with partners on exploring funding incentives for additional streetscape improvements, such as adopting a tree or a planter (similar to the memorial bench and rack with plaque program).
72. Maintain a healthy downtown street tree canopy; seek to ensure obstruction-free sidewalks as well as proper tree health and growth capacity.
73. Include green infrastructure in public improvement projects whenever feasible.
City of San Luis Obispo Community Forest Plan C. Hamma
Professional Project Report: Master of City & Regional Planning Program Page 62 of 91 Public feedback received during DCP meetings and workshops mooted the possibility of establishing a “tree conservation corps” focused on tree preservation, expressed support for a thriving tree canopy in general, and called for the annual evaluation and, if needed, replacement of tree grates to ensure both pedestrian safety and tree health.
The MPCP highlights two trees of interest that could be publicized, for instance, by being highlighted as part of a walking tour of downtown:
15. Living Holiday Tree
20. Moon Tree Interpretive Exhibit
2. Downtown’s Big Trees
Downtown San Luis Obispo would be unrecognizable to most locals without its big, beautiful trees – notably including its iconic, roughly 60-year old Indian laurel figs (Ficus microcarpa).
These enormous evergreen trees were planted widely across urban California during a beautification craze in the 1960s, based on their reputation as hardy “miracle trees” that could withstand heat, drought, air pollution, and anything else a city could throw at them (Gordon, 1996).
These trees dominate the central business district in San Luis Obispo and many other cities in California, contributing tremendously to aesthetics and sense of walkability. Their large, shady canopies confer a pleasing “sense of place” that encourages spending time outdoors, whether alone or in social gatherings, and increases contentment. The presence of these trees raises property values and drives increased retail business traffic.
However, the same trees drop leaves, twigs, and fruit on pedestrian walkways; attract birds and insects that can cause distress by entering businesses; block views and street signs; invade sewer lines; and, crucially, incur ongoing taxpayer expense through their need for expensive pruning and – even worse – expose cities to liability from falls caused by their upheaval of sidewalks.
Furthermore, according to Cal Poly’s SelecTree website, Ficus microcarpa’s branch strength is “medium weak,” they are a potential human health irritant due to the allergens and latexcontaining sap they produce, and they are not “powerline friendly” (SelecTree/UFEI, 1995- 2022).
By the mid-1990s, cities throughout California had either stopped planting Ficus microcarpa for these reasons, or were actively tearing them out and replacing them with palms, often to the consternation of tree lovers (Gordon, 1996). Some southern California cities, reluctant to cut down these popular features of their downtowns, have opted to play the waiting game by
City of San Luis Obispo Community Forest Plan C. Hamma
Professional Project Report: Master of City & Regional Planning Program Page 63 of 91 performing root trimming, installing underground root barriers, and replacing sidewalks with stone pavers around the trees – but the overall feeling on the part of arboricultural professionals seems to be that this is a case of “wrong tree, wrong place.” Stakeholders interviewed for the CFP mostly echoed this sentiment; there is a sense that as impressive and enjoyable as these trees are, they have gotten too big for their surroundings.
As the number of Ficus and other large, 1960s-era trees in downtown San Luis Obispo slowly dwindles through attrition, a replacement program based on planned rotation and “right tree, right place” principles is likely. The plan is for a regular 20- to 30-year replacement cycle to be put in place – some of the same species, including Ficus macrocarpa, may be replanted, but they will not be allowed to again attain such enormous size in cramped sidewalk spaces. In future decades, the vision for downtown SLO is that it will have a more diverse, mixed-age and mixedspecies tree palette containing a preponderance of species that, while still beautiful and inspiring, do not have the potential to grow as large as the current specimens and cause the aforementioned problems.
H. Increase Outreach to Officials and the Public
Several CFP interviewees stressed the importance of using outreach to build support for initiatives that are intended to improve quality of life for City residents and visitors. Outreach is essential because although research has found that overall public support for tree planting is high, trees also have downsides. They can be messy, damage sidewalks and underground utilities, comprise a safety hazard by dropping limbs or falling, attract insects, trigger allergies with their pollen, block views, and be expensive to water and maintain (Conway and Bang, 2014; Roman et al., 2020; Ziska et al., 2019). In addition, some tree species emit high levels of volatile organic compounds (VOCs) that may contribute to the formation of ground-level ozone when combined with human-generated pollutants (Churkina et al., 2017).4 Furthermore, many urban forest benefits are intangible and therefore not obvious and/or meaningful to the general public; residential planting and removal of trees is based far more on personal preferences such as aesthetics or maintenance concerns than on consideration of treerelated ecosystem services (Conway, 2016). In general, it can be assumed that tree-based information highlighting benefits that are more inherently obvious to the general public (e.g., landscape beautification, cooling and reduced energy bills, wildlife habitat) should have a greater impact on driving support for the urban forest than would information requiring more specialized knowledge, for instance regarding ecosystem services like air pollution removal or reduction of flooding and erosion. However, given that the dollar value of environmental services provided to a city by urban trees can easily be in the millions of dollars (in costs 4 Having said all that, many of these undesirable effects can be minimized through planning and regular maintenance.
City of San Luis Obispo Community Forest Plan C. Hamma
Professional Project Report: Master of City & Regional Planning Program Page 64 of 91 avoided) annually, the City still might consider broadly publicizing ecosystem services as a reason for continued support and growth of the taxpayer-funded urban forest program.
The City and its partners can enhance public buy-in to urban forestry efforts by continuing with existing outreach programs, creating new ones, and by planning for and hosting special events.
One “low-hanging fruit” example would be to maintain the City’s existing Tree City USA designation with the Arbor Day Foundation. As of this writing, San Luis Obispo has been a Tree City USA participant for 38 years. The participation requirements include maintaining a tree board or department, having a community tree ordinance, spending at least $2 per capita on urban forestry, and celebrating Arbor Day (Arbor Day Foundation, 2022). The City has also been the recipient of two Gold Leaf Awards from the International Society of Arboriculture (ISA).
Many other outreach opportunities were identified by CFP interviewees; please see Section XI.H, Recommendations (Outreach).
I. Address Equity Issues
It is well documented that green infrastructure like urban forest cover and the associated benefits are not equitably distributed in the US (Heynen et al., 2006; Landry and Chakraborty, 2009). Urban neighborhoods that were targeted for systematic disinvestment in the past (i.e., redlining) commonly lack adequate tree cover and other landscaping (Locke et al., 2020), which deprives residents of access to tree-related benefits and exacerbates the urban heat island effect, resulting in temperatures that can be significantly higher than in wealthier, tree-lined areas in the same city (Wilson, 2020). This issue takes on even more importance in the context of increasingly severe climate change effects (e.g., extreme heat, drought, wildfire, flooding).
The cumulative result is poorer public health and safety outcomes for the residents of these neighborhoods, leading to the question, “How can a city ensure that environmental, social, and economic benefits provided by the urban forest are equally distributed across all residents and neighborhoods, both now and in the future?”
In San Luis Obispo, Diversity, Equity, and Inclusion (DEI) is both a Major City Goal in the 2021- 2023 Financial Plan and an important component of the 2020 Climate Action Plan for Community Recovery. Davey Resource Group (DRG) addressed the topic of equity in their Urban Forestry Organizational Assessment for the City Public Works Department (Davey Resource Group, 2021). The Organizational Assessment states that while maintenance of trees in the public right-of-way is equally distributed across the entire city and public parks are located throughout the City, there are generally more opportunities for tree planting in newer neighborhoods than in older ones. However, there is considerable uncertainty around this topic.
Among residents who responded to the urban forest poll conducted by Davey as part of the Organizational Assessment, 63% of respondents were unsure whether urban forest benefits are equally accessible to all; 20% said they are not.
City of San Luis Obispo Community Forest Plan C. Hamma
Professional Project Report: Master of City & Regional Planning Program Page 65 of 91 The DRG Organizational Assessment included the following recommendations regarding equity:
• Conduct an assessment to explore the distribution of public tree canopy and associated benefits by neighborhood, census tract, and/or other geographic metrics • Coordinate with the City’s Diversity, Equity, and Inclusion Task Force to identify gaps in equity as regards urban forest access and benefits
• Develop equity strategies around the urban forest.
The nonprofit organization American Forests maintains an online data tool called Tree Equity Score that estimates the equitability of tree canopy distribution in a city based on tree canopy cover, climate, and demographic and socioeconomic data (American Forests, 2022). The result is a score (0 = lowest, 100 = highest) that is calculated at the neighborhood (Census block group) level and aggregated to the municipal level.
San Luis Obispo has an overall Tree Equity Score of 74 out of 100 (Treeequityscore.org, 2022).
The two highest scoring block groups are located between Broad Street and Santa Rosa Street, south of Foothill Boulevard and north of US 101 (score = 94; canopy cover = 27%), and an area mostly south of Foothill Boulevard including Ramona Drive and La Entrada Avenue (score = 91; canopy cover = 21%). The two lowest scoring block groups are an area around S. Higuera Street that includes Elks Lane, Bridge Street, and Fontana Avenue (score = 55; canopy cover = 9%) and the area immediately to the south of that but north of Tank Farm Road (score = 46; canopy cover = 7%). The Cal Poly campus, although not within the city limits, also earned a low score, 49 (canopy cover = 12%).
City of San Luis Obispo Community Forest Plan C. Hamma
Professional Project Report: Master of City & Regional Planning Program Page 66 of 91 X. Goals
Goals can be thought of as a high-level “road map” providing a framework for prioritizing proposed actions and evaluating the success of one’s efforts. The following CFP goals are proposals that were written by the author based on the stakeholder interviews, academic literature review, and review of other cities’ urban forest management plans conducted for this project. The topics addressed by these goals include forest health and expansion, funding and staffing, collaboration/cooperation, climate resilience, outreach to the public, and equity/justice.
• Maintain and enhance San Luis Obispo’s urban forest in order to maximize environmental, social, and economic benefits for all, while minimizing undesirable conditions
• Work to ensure adequate, sustained funding and staffing in order to implement the City’s identified urban forest priorities
• Emphasize the planting and care of climate-ready trees in locations where they will have the greatest chances of success in environmental conditions that are rapidly becoming more challenging (i.e., “right tree, right place”)
• Foster a spirit of collaboration between and within City departments that are involved in urban forest management, as well as between the City and other local stakeholders (e.g., community groups, nonprofit organizations, utilities, other cities, Cal Poly, other State agencies)
• Educate and seek the involvement of City residents and visitors, including historically marginalized groups, in order to obtain their buy-in and support for a thriving urban forest.
City of San Luis Obispo Community Forest Plan C. Hamma
Professional Project Report: Master of City & Regional Planning Program Page 67 of 91 XI. Recommendations
As with the CFP goals in Section X, the recommendations presented here are based on the research conducted for this project, but at a much finer-grained level. The recommendations are split into nine sections that match the format of Section IX, Findings of Stakeholder and Technical Expert Interviews. As of this writing, these recommendations have been through several iterations. It is the author’s intention that they will continue to be refined until they, and the entire CFP, are in a form acceptable for presentation to the San Luis Obispo City Council.
A. Funding
• Develop a sustainable funding plan that looks further into the future than just the current two-year budget cycle
• Continue to seek out creative new sources of funding for the urban forest program, possibly including grants, new tax revenue sources (e.g., a parcel tax), general obligation bonds, an assessment district, sponsorships, donations
• Modify fee/permit structures and direct additional revenues into an urban forestspecific fund that allows for detailed tracking of costs and available funds to facilitate the assessment of program effectiveness and inform future budget discussions • Consider basing tree removal fees (and replacement requirements) on the value of individual trees removed or on alternative methods (see Section IX.A, Ensure Adequate Funding)
• Consider hiring an economic consultant to conduct an urban forest financing study.
B. Staffing
• Continue to emphasize to elected officials the need for adequate staffing, which follows from adequate funding
• Determine the actual level of staffing needed, desired proportion of City staff to contractor personnel, and location of City staff within the City’s organizational chart • Create a new internal, interdepartmental urban forest working group along the lines of the “Green Team,” or create one as a subset of the existing Green Team • Ensure that the City’s new urban forest program director is a qualified urban forester (or has a similar background) who is experienced at working with elected officials, advisory bodies, and the public
• Ensure that at least one of the program director’s assistant managers is a certified arborist who may serve as City liaison to the Tree Committee • Consider hiring the following new City staff positions:
City of San Luis Obispo Community Forest Plan C. Hamma
Professional Project Report: Master of City & Regional Planning Program Page 68 of 91 o Development review arborist
o Volunteer coordinator
o For temporary office help, consider AmeriCorps and/or CivicSpark hires • Continue to cultivate relationships with the City’s external partners, who bring substantial value to the urban forest program through the provision of professional knowledge and/or volunteer labor
• Consider approaching Cal Poly and/or Cuesta College to create a new student urban forest steward program.
C. Complete Program Analysis and New Tree Inventory; Accrue and Analyze Data • Consider augmenting the 2022 West Coast Arborists tree inventory data with the acquisition of current LIDAR data, which would allow for more in-depth analysis of the City’s urban forest – in particular, trees on private property, which presumably account for the majority of trees within the City limits (possibly excluding open space areas) • Identify desired urban forest targets and a science-based, feasible set of metrics for long-term data collection
• Support the creation and public use of a website for the 10 Tall tree planting initiative • Consider contracting with an urban forestry consultant to evaluate progress towards targets and to quantify and place dollar values on the ecosystem services provided by City trees, e.g., using a software package such as i-Tree Eco • Provide the results to elected officials and the public in annual reports • Consider conducting additional public surveys beyond that carried out in 2021 by Davey Resource Group for their Organizational Assessment
• Plan to repeat the City tree inventory and subsequently update the CFP every five or 10 years. Updating the inventory will facilitate assessment of progress towards targets/goals, illuminate trends in forest growth and health, and inform any proposed changes in management practices, all of which can then be reported in the updated CFP.
D. Strengthen Maintenance Practices and Clear the Backlog • Place the highest possible priority on catching up on deferred maintenance so as to maximize urban forest growth and benefits while limiting preventable tree decline and death
• Continue to work with CalFire and other City partners to identify and reduce or mitigate wildland fire hazards, including threats to wildland-urban interface (WUI) neighborhoods, as described in the Chapter 3 of the City General Plan Safety Element
City of San Luis Obispo Community Forest Plan C. Hamma
Professional Project Report: Master of City & Regional Planning Program Page 69 of 91 • Continue to identify and proactively respond to hazardous tree situations on public and private property, as described in the Chapter 8 of the City General Plan Safety Element • Implement ad hoc, proactive “windshield surveys” by City staff each year to identify existing or incipient problems while they are still relatively minor and easily addressed • Consider having new pruning contractors Davey Tree Expert Company and West Coast Arborists implement multiple, concurrent pruning cycles in order to reduce workload on City staff and provide a tailored approach that may better promote tree health • Create a street tree replacement plan that requires timely replacement of dead/removed trees and provides recommended tree species, rootstocks, and rotation cycles in order to proactively address the recurring issue of tree-related sidewalk, foundation, and underground utility damage
o Specifically, address plans for the intended replacement of large downtown street trees, as these are the subject of high community interest.
E. Increase New Plantings
• Prepare a detailed and comprehensive planting plan for City trees; examples of relevant topics would include:
o “Right tree, right place” considerations such as species and size recommendations for specific (1) planting locations (sidewalk parkway vs. bulbout vs. street median vs. City park, etc.) and (2) sizes of planting spaces (open, moderately constrained, highly constrained…)
o Installation procedures, such as proper use of compost, soil enhancement technologies, irrigation, other equipment such as grow tubes, stakes, grates, etc.
o Optionally, a brief section containing early-life maintenance tips • Support and work with the 10 Tall campaign to plant 10,000 new trees within the City by 2035
o Achieve 100% stocking of the City’s approximately 350 empty tree wells o Determine how many new trees the City’s parks can accommodate o Conduct an equity analysis to determine where new plantings can best address environmental injustice issues in the city
o Continue working with City partners to recruit volunteer labor for planting events and, as possible, long-term care (e.g., watering) ▪ Consider using CCC or other labor sources for these purposes ▪ Ensure that whenever unskilled (e.g., volunteer) labor is used, adequate training on the planting and care of trees is provided
City of San Luis Obispo Community Forest Plan C. Hamma
Professional Project Report: Master of City & Regional Planning Program Page 70 of 91 o Conduct outreach via online/social media poll, newspaper ads, utility bill inserts, etc. to determine whether City property owners would be interested in an annual, free tree giveaway and planting program
• Consider using street bulbouts for the planting of smaller street trees • Consider modifying the City’s engineering standards for the number of street trees required per linear foot in new development, e.g., from one tree every 35 feet to one tree every 25 or 30 feet, based on species size at maturity or on a size class list, as deemed appropriate by a City arborist
• Increase the City’s required tree removal replacement ratios, e.g., from 1:1 onsite/2:1 offsite to 2:1 onsite/3:1 offsite
o Alternatively, base required replacement ratios on calculated ecosystem services value per tree, or on a specific percentage of total diameter removed o In cases where it is not feasible for a property owner to replant, consider allowing the owner to pay an in-lieu fee into a dedicated urban forestry fund, or to donate a tree to the City or a City tree-planting partner • Consider setting a minimum size requirement of 1.5” diameter at breast height (DBH) for all new street and park tree plantings
• Wherever possible, position new plantings on the east or west sides of buildings to maximize cooling from shade and reduce energy costs, while avoiding blocking the southern exposure that provides passive solar heating during winter • Evaluate an urban green roofs, walls, and balconies incentive program that could incorporate small trees.
F. Focus on Sustainability
• Adopt “right tree, right place” as the City’s tree planting philosophy going forward o “Right tree” means…
▪ Plant species that are considered suitable for urban spaces, provide abundant environmental, social, and economic benefits, and are climate-ready (hardy, tolerant of drought, heat, wind, etc.) ▪ Continue working with partners including Cal Poly San Luis Obispo’s Urban Forest Ecosystem Institute (UFEI) and interested growers to identify novel candidate species
o “Right place” means….
▪ Plant in locations that are most conducive to the long-term health and growth of the desired species, or where structural soils or similar technologies can be used to enhance tree growth potential (e.g., areas
City of San Luis Obispo Community Forest Plan C. Hamma
Professional Project Report: Master of City & Regional Planning Program Page 71 of 91 of poor soil conditions or with large amounts of impervious surface nearby)
▪ Plant trees in locations where their benefits will be maximized (e.g., for maximum shading of homes, buildings, parking lots, active transportation corridors/hubs…) and/or where they are most lacking (in greenery-poor parts of the city)
▪ Minimize potential for conflicts with urban infrastructure (e.g., under power lines, atop underground utilities…)
• Consider using known tree health-enhancing soil amendments and/or technologies when planting and maintaining trees
o The City may choose to use part of its required annual procurement of compost under SB 1383 in this manner
o The City may choose to modify the Municipal Code or engineering standards to require the use of technologies including engineered soils, soil cells, or other products that enhance infiltration and root growth as a condition of new development in areas with poor soil characteristics or extensive impermeable surfaces
• Adopt a lifecycle perspective toward urban trees
o Prepare a detailed and comprehensive lifecycle plan for City trees which includes succession planting and replacement strategies for aging street and park trees
o Emphasize long-term tree care and health over merely “planting trees” o Consider working with Cal Poly to establish an urban tree nursery, in which students would grow trees for the City
o Plan for end-of-life removal and sustainable use of the lumber, including:
▪ Uses that store carbon indefinitely (e.g., furniture, fencing, art) ▪ Uses that generate landscaping products (e.g., compost, fertilizer) ▪ Uses that reduce fossil fuel dependence by generating bioenergy (e.g., biogas, biofuels)
o Work with the City’s external partners to publicize these uses • Recognize the importance of age and species diversity in shaping the urban forest o Revise, and plan for the ongoing revision of, the City’s master tree list(s) in order to attain a palette of suitable, beneficial, and resilient species
City of San Luis Obispo Community Forest Plan C. Hamma
Professional Project Report: Master of City & Regional Planning Program Page 72 of 91 o Adhere to the rule of thumb described in Santamour (1990) that no single species should represent more than 10% of the total population and no single genus more than 20% (Santamour, 1990)
• Continue to coordinate with City partners to prepare for safety hazards including wildfire, flooding, and hazardous trees as referenced in the City General Plan Safety Element and the Multi-Jurisdictional Local Hazard Mitigation Plan o Consider working with CalFire to create an updated wildland-urban interface (WUI) fire severity map for the city
o Continue working with CalFire, the City Fire Department, and the Fire Safe Council to publicize the importance of fire prevention efforts, including defensible space regulations, on private property in the WUI o Identify locations within the City’s creek drainages where flooding could be exacerbated by fallen trees in the wake of storms, wildfires, or other large-scale tree mortality events
o Take into account existing and projected disease/pest problems when making species choices for purchasing and planting; consider reducing reliance on the most heavily affected host tree species. Pathogens and pests of concern include Monterey pine pitch canker (MPPC), sudden oak death (SOD), invasive shot hole borer (ISHB), goldspotted oak borer (GSOB)
o Work with contractors and partners (SLO County, CalFire, Cal Poly, PG&E, others) to monitor tree health citywide, including for unfolding pest and disease infestations; plan for a coordinated response to threats • Determine what the future holds for the Tree Committee • Give high priority to water conservation in all urban forest-related actions o Expedite the elimination of high water use tree species from the City master tree lists; going forward, allow only drought-tolerant species/varieties to be planted in the City
o Require installation (possibly temporary) of drip irrigation, using irrigation timers, as deemed necessary to support new plantings for the first two to three years
o Alternatively, consider requiring that each newly planted City tree be accompanied by a small, buried reservoir (olla) that is easily filled and slowly releases water into the ground; these may be porous clay pots or even perforated plastic jugs
o Working together with City partners, perform outreach to property owners about correct watering of trees during drought conditions
City of San Luis Obispo Community Forest Plan C. Hamma
Professional Project Report: Master of City & Regional Planning Program Page 73 of 91 o Modify City code to require that all aboveground watering (whether computercontrolled or by hand) take place during the hours of 7 pm – 9 am every day (i.e., prohibit watering between 9 am and 7 pm)
o Where possible, plant new trees near natural drainages (e.g., in open space) o In hardscape areas, consider redirecting stormwater runoff to new plantings o Mulch all new plantings; check once a year and add more mulch as needed o Consider or pilot the use of technologies such as engineered soils, soil cells, hydrogels, pervious (permeable) hardscape materials, etc. to improve soil structure, water infiltration/percolation, and therefore overall tree health • Make improvements to the City Municipal Code:
o Consider moving existing (or strengthened) City engineering standards around tree planting and care (including irrigation) into the Municipal Code, as a means of ensuring better outcomes in new development and landscaping o Require that the City consider species diversity, age/size diversity, and climate resilience when reviewing and approving planting plans for new developments • Use up-to-date resources such as the USDA Forest Service’s recent guide, “Climate Adaptation Actions for Urban Forests and Human Health” (Janowiak et al., 2021) to guide City policy and actions; this publication’s strategies include the following:
o Activate social systems for equitable climate adaptation, urban forest, and human health outcomes
o Reduce the impact of human health threats and stressors using urban trees and forests
o Maintain or increase extent of urban forests and vegetative cover o Sustain or restore fundamental ecological functions of urban ecosystems o Reduce the impact of physical and biological stressors on urban forests o Enhance taxonomic, functional, and structural diversity o Alter urban ecosystems toward new and expected conditions o Promote mental and social health in response to climate change o Promote human health co-benefits in nature-based climate adaptation.
G. Address Issues Unique to Downtown
• Support implementation of the City’s Downtown Concept Plan (DCP) and Mission Plaza Concept Plan (MPCP)
City of San Luis Obispo Community Forest Plan C. Hamma
Professional Project Report: Master of City & Regional Planning Program Page 74 of 91 • Continue to work with partners on additional downtown streetscape improvements (e.g., tree or planter adoption, memorial benches/public art using recycled urban lumber, the “rack with plaque” program) as described in the DCP • Continue to support collaborative efforts between Public Works, the Office of Sustainability, and City partners (e.g., Downtown SLO) to address tree-related problems affecting the downtown area, such as sidewalk damage and undesirable conditions due to insect and bird activity
• Consider requiring or incentivizing the creation of additional green infrastructure (e.g., green roofs, green walls) in public improvement projects in the downtown area • Establish a “tree conservation corps” – possibly an expansion of the existing Downtown Foresters volunteer group
• Consider creating and publicizing a walking tour of downtown that specifically calls out unique or otherwise notable trees (e.g., Living Holiday Tree, Moon Tree) among other points of interest
• Prioritize the evaluation and if needed, replacement, of downtown’s tree grates to ensure both pedestrian safety and tree health.
H. Increase Outreach to Officials and the Public
• Continue to maintain the City’s decades-long Arbor Day Foundation designation as a “Tree City USA”
• Work with City partners to create an “urban forestry community outreach week,” or combine this with the City’s Earth Day celebrations
• Tie in urban forestry outreach with other City marketing/tourism-oriented programs • Create a tree-focused downtown walking tour and/or a Citywide driving tour highlighting unique or outstanding trees, and providing information on urban forest facts and benefits on plaques or tree tags
• Initiate a program to provide financial support to income-qualifying private landowners for needed care and maintenance of their trees
• Use more storytelling in the urban forestry program; honor volunteers, sponsors, etc. • Promote the use of recycled urban lumber for projects like public art, furniture, sheds, benches, planters, and so on in order to store the wood’s carbon indefinitely • Try to attract statewide or national urban forestry conferences to San Luis Obispo (e.g., California Urban Forestry Council, Western Chapter of the International Society of Arboriculture [ISA], …)
• Create a City community tree planting and care program (a “tree corps”) featuring training by knowledgeable local stakeholders
City of San Luis Obispo Community Forest Plan C. Hamma
Professional Project Report: Master of City & Regional Planning Program Page 75 of 91 • Work with City partners, Cal Poly, and/or Cuesta College to create an urban forestry club • Update/improve the City’s urban forest website
o Make the City’s pruning schedule/plan available to public o Create a publicly viewable, interactive online map of all City-owned trees, a la City of Santa Monica or Cal Poly SLO
o Require monitoring and annual reporting on urban forest to the public; this could include dollar values as calculated via i-Tree Eco or similar software • Create a mobile app for City residents to make service requests, report new tree plantings, receive City urban forestry news, etc. (similar to Fresno’s “FresGO”) • Support the development and use of the 10 Tall website.
I. Address Equity Issues
• Focus additional attention in City urban forest planning to parts of the city that are on the lower end of the socioeconomic scale and/or currently have little in the way of green infrastructure, for instance, as identified by American Forests’ Tree Equity Score tool
• Work closely with residents in each proposed planting neighborhood to plan tree plantings and maintenance, as resident buy-in and participation are crucial to build the trust and pride that lead to long-term success
• Continue to conduct City outreach in, at a minimum, both English and Spanish languages; consider additional languages as well, if deemed warranted based on US Census data or other demographic information.
City of San Luis Obispo Community Forest Plan C. Hamma
Professional Project Report: Master of City & Regional Planning Program Page 76 of 91 XII. Next Steps
This draft Community Forest Plan was prepared in order to satisfy the “culminating experience” requirement for the Master of City & Regional Planning program at California Polytechnic State University, San Luis Obispo. The document therefore contains certain sections, such as Methodology and Literature Review, which are more applicable to an academic research paper than to a municipal planning document.
Over the next several months, the draft CFP will be revised and streamlined so that it adheres more closely to the format of a proper municipal management plan. Implementation matrices showing proposed timelines and budgets may be added. The results of a planned Public Works study session with the City Council this summer or fall will likely inform these revisions. Once deemed complete, the plan will be circulated to City staff for comments, edited again, and then presented to the San Luis Obispo City Council for consideration and, it is hoped, adoption.
City of San Luis Obispo Community Forest Plan C. Hamma
Professional Project Report: Master of City & Regional Planning Program Page 77 of 91 XIII. References
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https://www.salon.com/2021/09/19/a-proposal-to-plant-a-trillion-trees-to-save-us-fromclimate-change-may-not-be-realistic-heres-why/ Rosza, M. (2022, April 22). A renowned environmentalist says we're understanding forests all wrong. Retrieved from: https://www.salon.com/2022/04/22/trillion-trees-climate-change/ San Luis Obispo County Historical Society. (1972, September 7, 8, 9). Program: Bicentennial Pageant, 1772-1972.
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City of San Luis Obispo Community Forest Plan C. Hamma
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City of San Luis Obispo
Work Plan
The tree work plan provides a roadmap by designating annual work to efficiently prioritize the maintenance needs of all of city trees. The work plans do not account for changes in priority maintenance needs. Staff will continue to schedule work based on the highest known maintenance priority. The highest level of priority maintenance should occur first. In other words, if a tree is recommended for a routine prune during the initial inventory collection, but a service request and/or further inspection indicates a heightened maintenance priority, lesser priorities should be organized accordingly.
Work plans include consideration for trees by geographic region. Years 1 through 5 correspond to grouped Districts on the Paving Area Map. In all areas, any identified priority maintenance will be followed by routine maintenance, and the establishment of an ongoing 5-year maintenance cycle.
Downtown is scheduled to receive maintenance every 2 years, other parts of the community are scheduled to receive maintenance every 5 years. Trees that need more frequent maintenance are considered “cyclebusters”. These trees are scheduled to receive maintenance every 3 years.
The following Districts are included in each year:
x Year 1: District 1 and District 2, also addressing cyclebusters from District 4 and District 5 x Year 2: District 3 and District 9, also addressing cyclebusters from District 6 x Year 3: District 4 and District 5, also addressing cyclebusters from District 7 and District 8 x Year 4: District 6 and District 9, also addressing cyclebusters from District 1 and District 2 x Year 5: District 7 and District 8, also addressing cyclebusters from District 3 and District 9 The work plan is based on the maintenance needs of the October 2022 tree inventory of 12,427 Citymaintained trees along streets, in medians, parks, and at city facilities. Following the work plan, the Urban Forest Services will provide routine maintenance to all trees during a 5-year period (Table 1).
Routine maintenance includes trees recommended for large and small routine prune as well as City maintained, and trim poorly structured and trees with no maintenance recommendation. The type of prune can provide managers with a general idea of the equipment needed to complete the task (small routine prunes should not require climbing equipment or aerial lifts). The cost of pruning is priced by the individual tree and the cost per tree increases as the size increases.
Patrol - diseased or declining includes 103 trees that have been flagged to receive periodic inspections to ensure any future maintenance needs are noticed. This is estimated as a flat annual rate.
All known removals (103 trees) and stump grinding for existing stumps (139) are scheduled in year 1.
Year 1 removals will be added to the work plan as maintenance task stump grind in year 2. In years 2 through 5, an estimated 25 removals and stump grindings will occur each year. If trees continue to receive proper maintenance this number may decline moving forward. Tree removal and stump grinding are priced as a scale depending on the size (inch DBH).
Year 1- Work Plan
x Routine Pruning: 2,077
x Pruning - Cyclebusters: 375
x Patrol - Diseased or Declining: 8
x Tree Removal & Stump Grinding: 242 (sum of DBH: 3,969 for all Districts scheduled removals and stump grind)
Year 1 Total Cost: $514,062
Year 2- Work Plan
x Routine Pruning: 2,552
x Pruning - Cyclebusters: 428
x Patrol - Diseased or Declining: 17
x Tree Removal & Stump Grinding: 10 (estimated sum of DBH: 384) Year 2 Total Cost: $518,193
Year 3- Work Plan
x Routine Pruning: 2,126
x Pruning - Cyclebusters: 376
x Patrol - Diseased or Declining: 21
x Tree Removal & Stump Grinding: 10 (estimated sum of DBH: 384) Year 3 Total Cost: $508,141
Year 4- Work Plan
x Routine Pruning: 1,944
x Pruning - Cyclebusters: 469
x Patrol - Diseased or Declining: 50
x Tree Removal & Stump Grinding: 10 (estimated sum of DBH: 384) Year 4 Total Cost: $587,565
Year 5- Work Plan
x Routine Pruning: 1,155
x Pruning - Cyclebusters: 502
x Patrol - Diseased or Declining: 7
x Tree Removal & Stump Grinding: 10 (estimated sum of DBH: 384) Year 5 Total Cost: $451,602
Based on the work plan, the average cost of tree maintenance after establishment is approximately $50 a tree per year. This estimation can be used to project the cost of routine maintenance as the tree inventory expands.
Planting Plan
The tree planting plan provides annual work plans for planting and maintaining new. The planting plan is based on vacant sites and tree and stump removals from the October 2022 tree inventory. In total, there were 414 available potential tree planting locations with an additional 242 sites becoming available after the identified removals (103) and stump grindings (139) are addressed from the work plan. The 414 available planting sites are addressed in the first two years of the planting plan. Plantings are also scheduled in years 3 through 5, after removal and stump grinding occur for the 242 additional sites. The cost of planting is priced by the individual tree and the cost per tree increases as the size increases. The planting plan estimated 80% of plantings being 15-gallon containers and 10% in the two larger sizes to accommodate larger trees in the downtown, main arterial roads and other frequently visited areas. Newly planted trees are scheduled to receive training pruning and other young tree maintenance such as regular watering, mulching, stake adjustment and removal. Trees are visited once a week during establishment (first three years). The cost for young tree maintenance was determined by estimating the amount of time staff spend on the task.
Year 1- Planting Plan
x Tree Planting: 184 (Districts 1, 2 ,4, 5, and 9)
x Young Tree Maintenance: 1,869 (1,649 and the 184 new planted trees) Year 1 Total Cost: $105,374
Year 2- Planting Plan
x Tree Planting: 230 (Districts 3, 6, 7, and 8)
x Young Tree Maintenance: 1,514 (2/3rds of the Year 1 trees scheduled for young tree maintenance (1,100) and the Year 1 (184) and Year 2 (230) new planted trees) Year 2 Total Cost: $112,141
Year 3- Planting Plan
x Tree Planting: 242 (all sites created from Year 1 and 2 removal/stump grinds in all Districts) x Young Tree Maintenance: 1,448 (1/3rd of the Year 1 trees scheduled for young tree maintenance (550) and the Year 1 (184), Year 2 (230), and Year 3 (242) new planted trees) Year 3 Total Cost: $112,141
Year 4- Planting Plan
x Tree Planting: 20 (estimated 10 removal/stump grinds from Years 2 and 3) x Young Tree Maintenance: 492 (Year 2 (230) Year 3 (242), and Year 4 (30) new planted trees) Year 4 Total Cost: $22,898
Year 5- Planting Plan
x Tree Planting: 20 (estimated 10 removal/stump grinds from Years 2 and 3) x Young Tree Maintenance: 282 (Year 3 (242), Year 4 (20), and Year 5 (20) new planted trees) Year 5 Total Cost: $16,641
This work plan and planting plan may be an over or under estimation of the actual costs of maintenance.
Some reasons the costs may fluctuate follow:
x Certain events may cause increased maintenance needs (e.g., storm event, pest or pathogen epidemic)
x Estimates are based on October 2022 data and the inventory is constantly changing x Annual increases in the cost of maintenance was set to 5%, this may change x Additional maintenance may be needed outside of the work plan x Planting or maintenance goals change
x Several areas of San Luis Obispo may require additional maintenance, separate from the routine work plan. For example, this may occur as clearance and safety pruning along bus routes and areas of town that have higher pedestrian traffic such as parks and greenbelts. Trees in these areas are candidates for more regular inspection and may involve heavier pruning than typical block pruning.
Table 1: 5-Year Work Plan
Year 1 Year 2 Year 3 Year 4 Year 5 Total 5-Year
Maintenance Activity Diameter Class (inches) Cost/tree # of Trees Total Cost Cost/tree # of Trees Total Cost Cost/tree # of Trees Total Cost Cost/tree # of Trees Total Cost Cost/tree # of Trees Total Cost Total Cost Routine Pruning - Trees
Ϭ५ϲΎ $47 530 $25,043 $50 505 $25,054 $52 ϲϬϵ $31,725 $55 ϯϱϵ Ψϭϵ͕ϲϯϳ $57 207 Ψϭϭ͕ϴϴϵ $113,347 ϳ५ϭϮ ΨϵϬ ϳϵϵ Ψϳϭ͕ϱϮϲ Ψϵϰ ϭ͕Ϭϯϲ Ψϵϳ͕ϯϴϬ Ψϵϵ 751 $74,121 $104 528 $54,717 ΨϭϬϵ ϯϲϬ Ψϯϵ͕ϭϳϮ Ψϯϯϲ͕ϵϭϲϭϯ५ϭϴ $184 382 ΨϳϬ͕ϭϵϯ Ψϭϵϯ 552 ΨϭϬϲ͕ϱϬϮ $203 ϯϲϲ Ψϳϰ͕ϭϰϲ $213 521 $110,824 $223 270 ΨϲϬ͕ϯϬϰ ΨϰϮϭ͕ϵϲϴ ϭϵ- 24 ΨϮϲϴ ϮϬϵ Ψϱϱ͕ϵϲϬ $281 Ϯϲϯ Ψϳϯ͕ϵϯϵ ΨϮϵϱ 202 Ψϱϵ͕ϲϮϵ $310 238 Ψϳϯ͕ϳϲϵ $325 171 Ψϱϱ͕ϲϱϮ Ψϯϭϴ͕ϵϱϬ 25-30 $341 ϲϵ ΨϮϯ͕ϱϰϲ $358 ϴϵ Ψϯϭ͕ϴϵϬ Ψϯϳϲ ϭϬϲ Ψϯϵ͕ϴϴϬ Ψϯϵϱ ϭϲϯ Ψϲϰ͕ϯϵϭ $415 88 Ψϯϲ͕ϱϬϮ Ψϭϵϲ͕ϮϬϵ 31-ϯϲ Ψϰϵϵ ϰϵ ΨϮϰ͕ϰϯϵ $524 45 ΨϮϯ͕ϱϲϲ $550 42 ΨϮϯ͕Ϭϵϱ $577 70 ΨϰϬ͕ϰϭϲ ΨϲϬϲ 30 $18,187 ΨϭϮϵ͕ϳϬϮ 37-42 ΨϲϬϰ 22 $13,283 Ψϲϯϰ 20 ΨϭϮ͕ϲϳϵ Ψϲϲϲ 28 Ψϭϴ͕ϲϯϴ Ψϲϵϵ 25 $17,473 $734 14 $10,274 ΨϳϮ͕ϯϰϲ 43+ $788 17 $13,388 $827 12 Ψϵ͕ϵϮϯ Ψϴϲϴ 22 Ψϭϵ͕ϭϬϭ ΨϵϭϮ 40 Ψϯϲ͕ϰϲϱ Ψϵϱϳ 15 $14,358 Ψϵϯ͕Ϯϯϰ Activity Total(s) 2,077 ΨϮϵϳ͕ϯϳϲ 2,522 ΨϯϴϬ͕ϵϯϮ Ϯ͕ϭϮϲ $340,334 ϭ͕ϵϰϰ Ψϰϭϳ͕ϲϵϭ 1,155 ΨϮϰϲ͕ϯϯϴ Ψϭ͕ϲϴϮ͕ϲϳϮ Cyclebusters
Palms
Washingtonia sp. $121 50 Ψϲ͕Ϭϯϴ $127 17 $2,155 $133 ϯϵ Ψϱ͕ϭϵϮ $140 15 ΨϮ͕Ϭϵϳ $147 10 Ψϭ͕ϰϲϴ Ψϭϲ͕ϵϰϵ Date Palm $551 88 $48,510 Ψϱϳϵ 18 ΨϭϬ͕ϰϭϵ ΨϲϬϴ 171 ΨϭϬϯ͕ϵϮϲ Ψϲϯϴ 18 $11,487 ΨϲϳϬ 108 ΨϳϮ͕ϯϲϱ ΨϮϰϲ͕ϳϬϲ Other Palm spp. $300 54 Ψϭϲ͕ϮϬϬ $315 47 $14,805 $331 47 $15,545 $347 50 Ψϭϳ͕ϯϲϰ Ψϯϲϱ ϰϲ Ψϭϲ͕ϳϳϰ ΨϴϬ͕ϲϴϵ Ficus spp.
Ϭ५ϲΎ $47 ϲ $284 $50 ϲ ΨϮϵϴ $52 5 ΨϮϲϬ $55 ϲ $328 $57 5 $287 $1,457 ϳ५ϭϮ ΨϵϬ 2 Ψϭϳϵ Ψϵϰ 12 $1,128 Ψϵϵ 3 ΨϮϵϲ $104 12 $1,244 ΨϭϬϵ 14 $1,523 $4,370 ϭϯ५ϭϴ $184 5 Ψϵϭϵ Ψϭϵϯ 15 ΨϮ͕ϴϵϰ $203 4 $810 $213 14 ΨϮ͕ϵϳϴ $223 15 $3,350 ΨϭϬ͕ϵϱϭ ϭϵ- 24 ΨϮϲϴ ϲ Ψϭ͕ϲϬϳ $281 ϭϲ Ψϰ͕ϰϵϴ ΨϮϵϱ 3 Ψϴϴϲ $310 22 Ψϲ͕ϴϭϵ $325 ϭϵ Ψϲ͕ϭϴϰ Ψϭϵ͕ϵϵϯ 25-30 $341 ϭϲ Ψϱ͕ϰϲϬ $358 ϯϲ ΨϭϮ͕ϴϵϵ Ψϯϳϲ ϲ $2,257 Ψϯϵϱ 48 Ψϭϴ͕ϵϲϮ $415 38 Ψϭϱ͕ϳϲϮ $55,341 31-ϯϲ Ψϰϵϵ 10 Ψϰ͕ϵϴϴ $524 ϭϵ Ψϵ͕ϵϱϬ $550 3 Ψϭ͕ϲϱϬ $577 27 Ψϭϱ͕ϱϴϵ ΨϲϬϲ 20 $11,518 Ψϰϯ͕ϲϵϰ 37-42 ΨϲϬϰ 0 $0 Ψϲϯϰ ϭϵ $12,045 Ψϲϲϲ 0 $0 Ψϲϵϵ ϭϵ Ψϭϯ͕Ϯϳϵ $734 ϭϵ $4,403 ΨϮϵ͕ϳϮϳ 43+ $788 0 $0 $827 ϲ Ψϰ͕ϵϲϭ Ψϴϲϴ 0 $0 ΨϵϭϮ ϲ $5,470 Ψϵϱϳ ϲ $5,743 Ψϭϲ͕ϭϳϰ Carrotwood
Ϭ५ϲΎ $47 ϲ $284 $50 11 Ψϱϰϲ $52 2 $104 $55 13 $711 $57 ϵ $517 ΨϮ͕ϭϲϭ ϳ५ϭϮ ΨϵϬ ϱϲ $5,013 Ψϵϰ 55 $5,170 Ψϵϵ 31 Ψϯ͕ϬϲϬ $104 ϲϵ $7,151 ΨϭϬϵ 48 $5,223 ΨϮϱ͕ϲϭϲ ϭϯ५ϭϴ $184 57 $10,474 Ψϭϵϯ 88 Ψϭϲ͕ϵϳϵ $203 ϰϲ Ψϵ͕ϯϭϵ $213 ϵϮ Ψϭϵ͕ϱϳϬ $223 ϵϮ $20,548 Ψϳϲ͕ϴϴϵ ϭϵ- 24 ΨϮϲϴ ϭϵ $5,087 $281 43 ΨϭϮ͕Ϭϴϵ ΨϮϵϱ 15 $4,428 $310 38 $11,778 $325 32 $10,414 Ψϰϯ͕ϳϵϳ 25-30 $341 0 $0 $358 15 $5,375 Ψϯϳϲ 1 Ψϯϳϲ Ψϯϵϱ 14 $5,531 $415 ϭϲ Ψϲ͕ϲϯϳ Ψϭϳ͕ϵϭϴ31-ϯϲ Ψϰϵϵ 0 $0 $524 4 ΨϮ͕Ϭϵϱ $550 0 $0 $577 5 $2,887 ΨϲϬϲ 4 $2,425 $7,407 37-42 ΨϲϬϰ 0 $0 Ψϲϯϰ 0 $0 Ψϲϲϲ 0 $0 Ψϲϵϵ 0 $0 $734 0 $0 $0 43+ $788 0 $0 $827 1 $827 Ψϴϲϴ 0 $0 ΨϵϭϮ 1 ΨϵϭϮ Ψϵϱϳ 1 Ψϵϱϳ ΨϮ͕ϲϵϲ Activity Total(s) 375 $105,040 428 Ψϭϭϵ͕ϭϯϮ ϯϳϲ Ψϭϰϴ͕ϭϬϵ ϰϲϵ $144,155 502 Ψϭϴϲ͕Ϭϵϵ $702,535 Patrol Diseased or Declining
Ϭ५ϲ $150 1 $150 $158 5 $788 Ψϭϲϱ 5 $827 $174 17 ΨϮ͕ϵϱϮ $182 0 $0 Ψϰ͕ϳϭϲ ϳ५ϭϮ $150 3 $450 $158 3 $473 Ψϭϲϱ 7 $1,158 $174 11 Ψϭ͕ϵϭϬ $182 1 $182 $4,173 ϭϯ५ϭϴ $150 0 $0 $158 7 $1,103 Ψϭϲϱ 5 $827 $174 8 Ψϭ͕ϯϴϵ $182 2 Ψϯϲϱ Ψϯ͕ϲϴϯ ϭϵ- 24 $150 2 $300 $158 0 $0 Ψϭϲϱ 2 $331 $174 ϲ $1,042 $182 2 Ψϯϲϱ $2,037 25-30 $150 2 $300 $158 0 $0 Ψϭϲϱ 2 $331 $174 5 Ψϴϲϴ $182 0 $0 Ψϭ͕ϰϵϵ 31-ϯϲ $150 0 $0 $158 0 $0 Ψϭϲϱ 0 $0 $174 3 $521 $182 2 Ψϯϲϱ Ψϴϴϲ37-42 $150 0 $0 $158 0 $0 Ψϭϲϱ 0 $0 $174 0 $0 $182 0 $0 $0
42+ $150 0 $0 $158 2 $315 Ψϭϲϱ 0 $0 $174 0 $0 $182 0 $0 $315 Activity Total(s) 8 $1,200 17 ΨϮ͕ϲϳϴ 21 $3,473 50 Ψϴ͕ϲϴϮ 7 Ψϭ͕Ϯϳϲ Ψϭϳ͕ϯϬϵ Tree Removal & Stump
Grinding
$/in. DBH
Sum DBH
$/in. DBH
Sum DBH
$/in. DBH
Sum DBH
$/in. DBH
Sum DBH $/in. DBH Sum DBH
Tree Removal $58 ϵϭϮ ΨϱϮ͕ϲϲϴ Ψϲϭ ϭϵϮ Ψϭϭ͕ϲϰϮ Ψϲϰ ϭϵϮ $12,225 Ψϲϳ ϭϵϮ ΨϭϮ͕ϴϯϲ $70 ϭϵϮ $13,478 $102,848 Stump Grind Ψϭϵ 3,057 $57,777 $20 ϭϵϮ $3,810 $21 ϭϵϮ $4,001 $22 ϭϵϮ $4,201 $23 ϭϵϮ $4,411 $74,200 Activity Total(s) ϯ͕ϵϲϵ $110,445 384 $15,453 384 Ψϭϲ͕ϮϮϱ 384 $17,037 384 $17,888 $177,048 Program Administration All Maintenance Activity Total 2,702 2,977 2,533 2,473 1,674 12,359 All Cost Total $514,062 $518,193 $508,141 $587,565 $451,602 $2,579,564 Table 2: Maintenance by District
District 1 District 2 District 3 District 4 District 5 District 6 District 7 District 8 District 9 Total Trees ϳϰϵ ϭ͕ϰϵϳ Ϯ͕Ϭϵϴ 1,205 1,127 1,488 ϱϮϵ ϳϵϲ ϳϱϲRoutine Pruning ϲϰϲ 1,431 2,055 ϭ͕ϭϬϵ 1,017 1,477 485 ϲϳϬ ϰϲϳCyclebuster Pruning 103 ϲϲ 43 ϵϲ 110 11 44 ϭϮϲ ϮϴϵPatrol - Diseased or Declining 5 3 14 ϭϵ 2 47 2 5 3 Tree and Stump Removal 14 23 38 14 ϵϮ 33 2 22 4 Total Maintenance Tasks 768 1,523 2,150 1,238 1,221 1,568 533 823 763 Table 3: 5-Year Planting Plan
Year 1 Year 2 Year 3 Year 4 Year 5 5-Year
Maintenance Activity Diameter Class (inches) Cost/tree # of Trees Total Cost Cost/tree # of Trees Total Cost Cost/tree # of Trees Total Cost Cost/tree # of Trees Total Cost Cost/tree # of Trees Total Cost Total Cost Tree Planting
15-gallon ΨϮϮϲ ϭϲϰ $37,023 $237 208 Ψϰϵ͕ϯϬϰ ΨϮϰϵ 218 $54,258 ΨϮϲϭ 18 $4,704 $274 18 Ψϰ͕ϵϯϵ $150,228 24-inch box $373 ϵ $3,355 Ψϯϵϭ 11 $4,305 $411 12 Ψϰ͕ϵϯϭ $432 1 $432 $453 1 $453 Ψϭϯ͕ϰϳϲ ϯϲ-inch box Ψϭ͕Ϭϳϲ 11 Ψϭϭ͕ϴϯϵ $1,130 11 $12,431 $1,187 12 Ψϭϰ͕Ϯϯϵ Ψϭ͕Ϯϰϲ 1 Ψϭ͕Ϯϰϲ $1,308 1 $1,308 Ψϰϭ͕ϬϲϮ Activity Total(s) $52,217 230 Ψϲϲ͕ϬϰϬ 242 $73,428 20 Ψϲ͕ϯϴϭ 20 Ψϲ͕ϳϬϬ ΨϮϬϰ͕ϳϲϲ Young Tree Maintenance Ϭ५ϭϮ ΨϮϵ 1,833 $53,157 $30 1,514 Ψϰϲ͕ϭϬϭ $32 1,448 Ψϰϲ͕Ϯϵϲ $34 ϰϵϮ Ψϭϲ͕ϱϭϳ $35 282 Ψϵ͕ϵϰϬ $172,012 Activity Total(s) 1,833 $53,157 1,514 Ψϰϲ͕ϭϬϭ 1,448 Ψϰϲ͕Ϯϵϲ ϰϵϮ Ψϭϲ͕ϱϭϳ 282 Ψϵ͕ϵϰϬ $172,012 Program Administration All Maintenance Activity Total 2,017 1,744 1,690 512 302 6,265 Cost Grand Total $105,374 $112,141 $119,724 $22,898 $16,641 376,778