Sustainable Development and Resilient Communities

City Tree Ordinances

Because of the immense value of planting and caring for trees, communities should consider implementing tree ordinances that establish clear guidelines and regulations for the maintenance and removal of trees on public and private lands. Comprehensive tree preservation ordinances can play a central role in successfully protecting trees during and after residential development.

SCAG Region Urban Greening Management Plan Examples

• Santa Monica Urban Forest site (includes Urban Forestry Master Plan, list of upcoming tree removals, Community Engagement Map, Urban Forest Task Force, Heritage Tree Map, and Drought Guide)
• South Pasadena Trees
• Sierra Madre Community Forest Management Plan

Resources for creating a Tree Ordinance

• Guidelines for Developing and Evaluating Tree Ordinances by the International Society of Arboriculture
• How To Write a Municipal Tree Ordinance by Tree City USA
• Tree Ordinance Overview by WeConservePA

Identifying Priority Areas for Tree Planting

Urban forestry programs can be used as one of the strategies to improve health, environmental and heat reduction outcomes in underresourced communities. which often lack parks and open spaces. The following resources may help you determine which areas to prioritize tree planting.

Resources to consider when prioritizing areas for tree planting

1. The USDA Forest Service Tree Canopy Data: This map overlays tree canopy coverage data at 60-cm spatial resolution, ozone and PM 2.5 pollution information, CalEPA’s urban heat island index, and other public health indicators. This map shows which areas lack tree canopy coverage, combined with low health indicators, to prioritize areas for tree planting.  
2. Multi-Resolution Land Characteristics (MRLC) Consortium: This resource provides land cover datasets at the national scale. 
3. California Healthy Places Index: This map shows data on social conditions that drive health such as education, economic opportunities, clean air and water, and other indicators. 
4. California Healthy Places Index: Extreme Heat Edition: This resource shows the number of days above 90 or 100 degrees at various time scales such as mid- and end-of-century down to cities and elementary school districts. It also shows other indicators such as tree canopy coverage (from the national land cover database), park acres, impervious surface cover, urban heat island index, PM 2.5, Diesel PM, ozone and more.

Tree Planting in a Changing Climate

Climate change is projected to cause changes in air temperatures, precipitation, disease frequencies and other factors that will affect the ability of trees in urban and natural forests to survive. The interactions of drought, heat stress and insect outbreaks due to climate change, as well as other factors, can lead to forest mortality in complex patterns. Drought-related tree mortality may even occur years or decades after the drought. Different sequences of climate events, such as a flood followed by a drought, can also affect tree growth and the risk of mortality. 

Selecting trees that are appropriate for the site and able to withstand a variety of landscape characteristics will be key in planting resilient, climate-ready urban forests. Communities should consider forming a tree list that includes a variety of different tree species that show promise in withstanding the local projected climate hazards. Please note that research into climate-ready trees is still in its early stages and there are information gaps on how climate change will impact tree survival rates. Here are the factors to consider when forming your tree list. Communities should determine priority based on their projected climate hazards. 

Consider plants that have low water requirements or are drought tolerant

Planting programs may want to prioritize trees that use low amounts of water because climate models predict that drought and heat waves will increase water loss from tree surfaces (evaporative demands).

Consider plants that can tolerate multiple water levels or soil moisture levels

In some regions, flooding will be an increased risk within this century. Selecting trees that have been known to be tolerant to multiple water levels may increase their ability to survive in projected flood-prone areas. There is limited information on tree species’ levels of tolerance to water levels. Communities should consider working with local arborists to identify trees that can tolerate high water levels if increased flooding is projected. 

Identify trees that can do well in new projected USDA hardiness zones

Select trees that can potentially do well in the projected future U.S. Department of Agriculture (USDA) Plant Hardiness Zones, minimum and maximum temperatures. 

Identify trees that can do well in new projected air temperature

Warmer temperatures alone can increase forest water stress independent of precipitation amount and can accelerate drought-induced mortality. Selecting species that have been known to thrive in multiple temperatures can potentially increase their chances of survival in a rapidly changing climate. 

Select trees with more tolerance for salinity levels

The SCAG region has been increasingly using recycled water, which tends to have higher salinity due to the water treatment process. Selecting species that have higher salinity tolerance may increase these trees’ chances of survival. 

Consider pest resilience in the tree palette

Climate change is projected to induce uncertain changes to pest environments. Due to warmer climates, some communities may experience new and longer pest seasons. Diverse species will decrease the chances that an urban forest made up of a singular species will be wiped out due to pests targeting that species.  

Consider native trees that can thrive and support biodiversity

Species diversity should be an important factor for communities when forming tree lists to account for both the need for the urban forest to provide habitat for native species and climate resiliency.

Create a plan for managing non-native and invasive species

Non-native plants are species that have not historically lived in one area but have been introduced by humans. Invasive species are also non-native but their introduction causes harm to the surrounding ecosystem. Communities should avoid the use of known invasive species and undertake continuous monitoring to ensure that any non-native species that are introduced do not cause harm to the local ecosystem. There is no source of information that comprehensively identifies which species will be invasive in a local area. Communities should utilize the best available resources and work with local arborists to select trees that have not been known to be invasive and plan for continuous monitoring.

Resources for Creating a Tree List

Projected risk factors and future climate

Risk Factor: This tool by the First Street Foundation allows you to see the projected risk factors of your city, including flood, extreme heat, fire and wind factors. 

Cal-Adapt: Cal-Adapt allows you to see projected mid-century (2035-2064) and end-century (2070-2099) annual average maximum and minimum temperatures, and annual average precipitation, broken down by cities, counties, congressional districts and other boundaries. 

Climate Assessment Tool: This tool allows you to see how suitable certain taxa, or groups of trees are to the future climate of a botanic garden’s location or by longitude and latitude coordinates. Not all species of plants and botanical gardens are included. The analysis of the climate suitability of species is based on mean annual temperature. 

Future Plant USDA Hardiness Zone: This interactive web tool by Davey Institute and Arbor Day Foundation allows you to see the projected new USDA Hardiness Zone of your area based on multiple emissions scenarios. 

USDA Hardiness Zone Map: The USDA Hardiness Zone Map allows you to identify your current USDA hardiness zone based on zip code. The map is based on the average annual minimum winter temperature. Although plants are often noted to show that they can live in certain USDA zones. A plant may still thrive in an area not indicated to match its USDA zone.

Tree characteristics

Climate Ready Trees: Climate Ready Trees is a resource compiled by a coalition of university, USDA forest service researchers, and ecological non-profits that highlights a number of trees that may be particularly suited to tolerate the stressors of a changing climate. 

SelecTree: SelecTree allows you to search California trees by tree characteristics such as whether they are native, height, tree shape, salinity tolerance, water use rating, sun exposure and landscape information such as USDA hardiness zone, sunset climate zone, utility precautions, available planting size, and more. 

The Water Use Classification of Landscape Species: This database by the UC Davis California Center for Urban Horticulture assigns ratings for irrigation needs from very low to high. 

CalScape: This resource by the California Native Plant Society can help you identify where, on a map, different native species are found in California. This resource also provides basic information about plant characteristics and how to care for them. 

Waterwise Garden Planner: This tool allows you to search for different California plants based on whether they’re native, plant type (trees or shrubs), evergreen or deciduous, water needs, sun exposure, aesthetics and functions. 

Where trees historically lived and invasiveness

CalScape: This resource by the California Native Plant Society can help you identify where, on a map, different native species are found in California. This resource also provides basic information about plant characteristics and how to care for them. 

Inventory of Invasive Plants: This list by the California Invasive Plant Council ranks the invasiveness of species. 

Guides on how to create your tree palette 

California Tree Palette for Schoolyard Forests: This resource by the Green Schoolyards of America is intended to help you identify trees that are climate-resilient and are appropriate for a schoolyard setting by sunset climate zones in California. 

Planning for resilient urban forests: A datadriven approach to assessing urban tree species suitability in California: This presentation by Natalie Love, Ph.D. describes a process by which communities can use to select a tree list for their city. 

Climate Change and Urban Forests: This presentation by Igor Lacan, UC Agriculture and Natural Resources, (UCANR) describes the space-for-time substitution process that can be used to identify tree species for a community’s future climate. 

Tree Species Selection Guidelines for the Albuquerque Metro Area: A study on identifying climate-ready trees by the Nature Conservancy for the Albuquerque area. 

List of locally specific climate-resilient trees considered by other organizations

California Tree Palette for Schoolyard Forests: This resource by the Green Schoolyards of America is intended to help identify trees that are climate-resilient and are appropriate for a schoolyard setting by sunset climate zones in California. 

Planting Resilience: Identifying Climate-Resilient Tree Species and Increasing Their Presence in Los Angeles’ Urban Forest: This study by the UCLA Luskin School of Public Affairs and TreePeople identified 28 climate-resilient tree species that show promise for Los Angeles County. 

Climate Ready Trees: Climate Ready Trees is a resource compiled by a coalition of university, USDA forest service researchers, and ecological non-profits that highlights a number of trees that may be particularly suited to tolerate the stressors of a changing climate. 

Tree Species Selection Guidelines for the Albuquerque Metro Area: A study on identifying climate-ready trees by the Nature Conservancy for the Albuquerque area.

References

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