2025 State of the Urban Forest
Boulder’s urban forest canopy is decreasing
Our Boulder Urban Canopy
Upright European Hornbeam tree located at Pearl and 30th Street
The city continues to see the percentage of the urban canopy trend downwards. This update to 2023's State of the Urban Forest Report analyzes our tree inventory, explains our resources and shows how we can all help our urban canopy grow now and in the future.
Boulder’s urban tree canopy is a layer of leaves, branches and stems of trees that provide shade and cover for the ground. It’s an effective, nature-based method for mitigating the effects of climate change while also providing a myriad of other environmental, social, health and economic benefits.
The higher the percentage of our urban tree canopy, the more benefits it provides to the community. However, as stated in the 2023 report, the urban canopy has decreased between 2013 and 2020.
Why are we seeing this trend and what progress has been made since 2023?
Urban canopy measurement methodology
The methodology used to calculate urban tree canopy, and the boundaries used for the analysis, have both changed since the Urban Forest Strategic Plan (UFSP) was approved in 2018. Instead of using city limits, our analysis now uses subcommunity boundaries to ensure better alignment with other citywide initiatives.
The overarching goal of the UFSP was to maintain 16% urban tree canopy, but we now know that number from 2018 is closer to 22% . This doesn’t mean the actual tree canopy grew but rather where, when and how we measure it has changed.
The city’s urban canopy is currently at 22%.
By making the shift to subcommunity, we can more easily see the canopy change and impacts on a neighborhood scale.
For example, three of the ten subcommunities within Boulder have shown no change in urban tree canopy between 2015 and 2021 and seven subcommunities have lost tree canopy in that timeframe.
Canopy change by subcommunity from 2015-2021
Across all Boulder subcommunities, from 2015 to 2021 the urban canopy stayed the same or decreased.
Palo Park
The slider maps show the loss of tree canopy (red dots) from 2015 to 2021. The city has added several new subdivisions with street trees over the past 8-10 years. These trees are now to the point where they are contributing to the canopy. Even with the new trees however, Palo Park experienced no overall canopy gain.
University Hill
The slider maps show the loss of tree canopy (red dots) from 2015 to 2021. Mature trees are being removed on both public and private property due to EAB, other pest issues and aging. Trees are also removed through private development and large city projects. New trees are being planted on public property, but tree removals are outpacing all tree planting.
Mature trees are crucial for climate change mitigation because their canopies are larger and they contribute more than new trees to heat moderation.
East Boulder map
Low-income communities, like in East Boulder, have fewer trees than other subcommunities making these populations more vulnerable to the impacts of climate change and more heat-related illnesses. In this map the darker red colors indicate a higher investment need in the subcommunity, and the green dots are trees.
Boulder Forestry accepts requests for street tree planting, but we receive fewer requests in less affluent, lower canopied areas. Request a free street tree .
Risks to the urban canopy
Kermes scale and drippy blight bacteria on a red oak tree
Losses due to Emerald Ash Borer (EAB) and other pests, severe weather events, and development have outpaced new planting and growth. More of the canopy is at risk, with up to 25% of it threatened by EAB alone, in addition to threats from other pest species like drippy blight , which is currently attacking our red oaks.
Drippy blight bacteria on a tree near the Bandshell
Looking ahead
The 2022 Boulder Parks and Recreation Plan helped us understand how our assets and services, including the urban tree canopy, are distributed throughout the city. This work identified gaps and areas where more investment is needed that can make the most impact for underserved members of the community. We are committed to improving the equitable distribution of our services.
Boulder's Urban Forest Strategic Report
In addition, BPR’s Urban Forest Strategic Plan (UFSP) is our roadmap to our goal of maintaining and exceeding our canopy cover throughout the city.
In 2018, the UFSP identified an annual $500,000 funding gap, based on average spending in comparable cities. This gap was highlighted in our Department Plan. Each year, that gap grows due to inflation and rising costs. Boulder Forestry continues to look for opportunities to close that funding gap as we care for our urban canopy.
A society grows great when old men plant trees whose shade they know they shall never sit in.
What are the climate impacts of trees?
Trees are incredibly important for our climate, especially in urban settings. You can feel the heat radiating off paved surfaces on hot days. Trees help cool down the ambient temperature around those heat islands.
- The temperature in urban areas can differ from 12-18° F between the hottest and coolest neighborhoods partially due to the differences in tree cover.
- Adding street trees can decrease temperatures by as much as 4° F.
- Canopy loss between 50-100% can increase temperatures by as much as 6° F.
- Planting trees in up to 50% of plantable spaces can decrease temperatures by as much as 9° F.
Extreme heat is the leading weather-related cause of death. Planting trees in the right places reduces the urban heat island effect and can help save lives.
Source: City of Boulder Urban Heat Risk Assessment, September 2024
What are additional benefits of trees?
We have a symbiotic relationship with trees…we need them, and they need us. Let’s work together and take action to ensure Boulder has a healthy, thriving, urban forest and preserve that relationship well into the future.
The Cool Boulder campaign
We partner with the city’s Climate Initiatives Department on the Cool Boulder campaign, which helps equip residents with the knowledge and tools needed to take affordable, impactful climate action. Learn more at CoolBoulder.org .
What can you do to help?
- Make sure the trees on your property have adequate water, are pruned routinely by a licensed, certified arborist, and are treated for pests, when needed.
- Plant and help new trees thrive. Proper planting, watering, mulching and maintenance helps them survive our climate.
- Advocate for tree planting, maintenance and protection in your neighborhood, your community or across the city.
- Request a free street tree! Boulder Forestry plants free trees into the public street rights-of-way adjacent to homes where there is enough room and an irrigation system to ensure adequate long-term watering. Request a tree .
- Become a tree tender with the PLAY Boulder Foundation Tree Trust.
- Be on the lookout for invasive pests! The earlier a new pest is detected the more management options are available. Be on the lookout for these tree pests: spotted lanternfly, Asian longhorned beetle and the spongy moth.
Spotted Lanternfly - image courtesy of PA Dept. of Agriculture
Spongy Moth caterpillar - image courtesy of Oleksandrum via Shutterstock
Christensen Park - photographer Belah Abel
Urban Forest Strategic Plan
The Urban Forest Strategic Plan (UFSP) is our roadmap to create a more resilient, sustainable urban forest by maintaining our urban tree canopy cover throughout the city.
The UFSP includes short and long-term goals to:
- increase community safety
- stabilize the urban tree canopy from losses
- improve the canopy’s overall health
We implement the plan through:
- increasing tree planting
- ongoing tree maintenance
- collaborating with local, regional, state and national partners
The UFSP identifies what could be accomplished with more funding. We're working to find additional funding to care for and grow the urban canopy.
Who implements Boulder's UFSP? We all do! The Boulder Forestry team takes care of the public trees in our city. Our urban forest consists of public and private trees, so we need your help.
Our in-house team of foresters, led by nationally recognized City Forester Kathleen Alexander, manage the 51,000 public trees in city parks and in the public street rights-of-way thrive, despite the challenges of extreme temperature swings, snowstorms, drought, floods, climate change, invasive pests, and the loss of trees due to development projects and construction.
Boulder Forestry achieves the goals of the Urban Forest Strategic Plan through smart planning (plan), effective management (manage), tree protection (protect) and community engagement (engage).
Here’s the progress we’re making along these four themes:
Plan
Progress
- Partnered with the city’s Climate Initiatives and Fire-Rescue Departments on climate resilient landscapes guidelines
- Updated canopy information
- Started utilizing new canopy software
- Analyzed diversity data from the updated tree inventory and canopy analysis to prioritize tree planting for future years
- Documented the Boulder Forestry emergency response standard operating procedures
Priorities looking ahead
- Diversify and add equity considerations to tree planting plans
- Continue interdepartmental work on Boulder Revised Code changes related to urban trees
Manage
Progress
Trees planted
- 906 trees in 2023-24, including 105 new trees at Flatirons Golf Course since 2020
Trees pruned
4,773 trees citywide in 2023-24, including 454 trees at Flatirons Golf Course since 2020
Ash trees removed by Boulder Forestry by year between 2013 and 2024
Additional accomplishments
- Recognized as a Tree City USA for the 41st year and as a Tree City of the World for the fifth year
- Continued the Emerald Ash Borer response , including increased tree planting, pesticides to preserve ash trees, using biocontrols, tree removals and continued outreach. Boulder Forestry staff was also invited to present information at a regional workshop in Billings, MT, a tree pest diagnostic workshop in Longmont, CO and to the National Plant Board.
- Responded to multiple small weather-related events that impacted public trees
- Updated the city’s public tree inventory
- Started tracking the survivability of newly planted trees
1,203 service requests completed from Jan 2023 to Oct. 2024
Priorities looking ahead
- Identifying additional funding for urban forest needs since there is a gap of nearly $500,000/year based on average spending in comparable cities
- Continuing our EAB response
- Monitoring for other invasive pests and tree health issues
Pests we’re monitoring include:
- Native pests that may spill over from the foothills such as mountain pine beetle or Douglas-fir tussock moth
- Kermes Scale/Drippy Blight impacting large red oak trees
- European elm scale in American elms
- Collaborating with the Community Vitality Department to improve site conditions to grow trees on the Hill and in downtown
- Phasing in additional monitoring and maintenance activities to enhance trees’ long-term survivability, such as increasing conversations with property owners about watering/mulching, structure pruning, and improving the growing conditions for newly planted trees
Protect
Progress
- Continued to partner with the Climate Initiatives, Planning and Development Services, and Fire-Rescue Departments on:
- code updates
- climate resilient landscapes guidelines
- complying with the new state turf law
- strengthening tree protection measures
Priorities looking ahead
- Continuing to partner with city departments on code changes
Engage
Progress
- Worked with Communications and Engagement staff to create an Urban Forest, Trees & Climate Impacts Communication Plan
- Worked with the inaugural class of the Community Forestry Corps
- Planted trees for Arbor Day with elementary school students from High Peaks BCSIS in 2023 and Whittier Elementary in 2024
- Planted trees with the CommuniTyler organization in 2023 and 2024
- Supported the PLAY Boulder Foundation’s Tree Trust program
- Tree giveaway at McGuckin Hardware in April 2023 and 2024
- Tree sale for the community in Fall 2023
- Participated for the fourth year in the Saluting Branches event at Fort Logan National Cemetery
- Provided tree related crafts for kids and talked with community members at the Chautauqua Meadow Music events in 2023 and 2024
- Talked with community members at the 2023 and 2024 What’s Up Boulder events
Priorities looking ahead
- Continuing support for the PLAY Boulder Foundation’s Tree Trust and the Community Forestry Corps programs
- Implementing items in the Urban Forest, Trees & Climate Impacts Communication Plan
- Continuing community outreach at public events
- Starting a conversation with the community about the need and desire to protect private property trees
Using the USFP as our guidebook, we will continue working to achieve our vision of a resilient and sustainable urban forest.
Tree Inventory & Resource Analysis
Boulder Forestry maintains a tree inventory and tracks all major tree maintenance to manage risk, monitor costs and assess future needs. Our tree inventory and resource analysis were both updated in 2024.
The public tree inventory:
- Contains information on tree species, diameter, condition, location, etc.
- Assesses overall health, growth and maintenance needs of our public trees
- Manages risk to and from our public trees
The tree resource analysis:
- Provides a baseline from which to measure changes, trends and outcomes
- Shows the number, diversity and size of trees
- Helps to identify trees’ susceptibility to current and future invasive pests and catastrophic events
- Indicates the maintenance work needed
- Evaluates the monetary value and benefits provided by our urban canopy
- Contains information to request adequate budget for current and future tree maintenance
Overall condition of trees maintained by Boulder Forestry
Diversity in tree species is good! Boulder Forestry's goal is to have each tree species less than 5% of all trees.
Map of public tree inventory
Investing in our future
With Boulder’s urban tree canopy trending downward, action is needed now to achieve our goal to maintain and grow the city’s urban tree canopy. This will require enormous effort, both public and private. This work can only be successful only with the support of our community and collaboration between public land managers and private landowners.
Here’s what Boulder Forestry is doing to reach the canopy goal:
- Maintain public street rights-of-way and park trees
- Manage Emerald Ash Borer and monitor for new pests
- Plant diverse tree species in low canopy areas and increase their care to help them survive
- Work with other city departments to make changes to the Boulder Revised Code that would strengthen protections for public trees and possibly add protections for private property trees
- Work with other departments on city projects to ensure trees are preserved, whenever possible
- Support the PLAY Boulder Foundation Tree Trust and the Community Forestry Corps
Trees touch everything. It’s an interdependent and a long-term relationship. The impact of a newly planted tree may not be fully realized for decades, so investment now is critical.
Conclusion
While momentum slowed during the pandemic to foster the urban canopy, we're working hard to achieve the goals of the Urban Forest Strategic Plan.
We hope this report helps you understand the importance of our urban canopy and all that the city and our community does to care for it!
Text and some photos from City of Boulder. Additional photos from Boulder community members. Click on the "i" to see who submitted each photo.
