Summer heat is not felt equally. Trees are one reason why.
A new online tool, developed by conservation nonprofit American Forests and the Washington Department of Natural Resources, lets Washington residents explore where those inequities exist. It covers urban areas across the state.
A fuller tree canopy comes with a host of benefits: It makes an area cooler, cleans the air, reduces stormwater runoff and makes streets safer for people with higher health risks, like seniors and children.
The tool assigns each city and census block group a tree equity score, which takes into account the area’s tree canopy need and socioeconomic context. The highest score possible is 100.
Take Montlake, for example: The Seattle neighborhood sandwiched between several large parks has average tree equity scores in the high 90s. Just a few miles away, parts of Chinatown International District score as low as 57. It can be more than 6 degrees Fahrenheit hotter there than the average temperature for Seattle. Further south in Rainier Valley, it can be more than 10 degrees hotter. These neighborhoods also have a higher proportion of people of color, children, seniors, people in poverty and households that speak a limited amount of English than Montlake. The scores not only reflect how healthy each neighborhood’s tree canopy is, but also represent other factors that increase residents’ risk during extreme heat.
The hottest areas in cities often align with socioeconomic, health and racial disparities, meaning those most vulnerable to extreme heat are the most likely to experience it.
“They’re not just decorative umbrellas,” said Will Rubin, DNR’s communications manager, of neighborhood trees, “they’re core, critical pieces of modern infrastructure.”
The tool comes out at a time when extreme heat is the No. 1 cause of weather-related deaths in the country, according to the National Weather Service. About 400 people in Washington died from direct and indirect heat-related causes during the 2021 heat dome in the Pacific Northwest, according to the University of Washington Climate Impacts Group.
In its wake, there was a surge in interest and investment in urban forestry, Rubin said. But the funding for work to reduce environmental inequities like low tree canopy today is less certain, especially at the federal level.
In April 2023, DNR and American Forests formed the Washington State Tree Equity Collaborative — the first statewide partnership of its kind.
DNR and American Forests described their roles as being supporters of local urban forestry initiatives, rather than on-the-ground directors. When it comes to actually getting hands in the dirt, it is largely individual community members, local nonprofits and city departments who are taking the lead.
“If we’re going to make progress on tree equity across the state, we really need to have community members involved in a way that feels authentic to them and empowers them to make choices about their own neighborhoods and how the land is managed,” said Lowell Wyse, executive director of the Tacoma Tree Foundation, a nonprofit focused on community greening efforts.
The dashboard
At its core, the tree equity score analyzer is a project planning tool, said Ben Thompson, DNR’s Urban and Community Forestry Program manager. But its user-friendly interface helps break down barriers so that anyone can talk about the quality of tree coverage in their community.
Each area’s score is based on two factors, according to Chris David, the vice president of geographic information systems and data science at American Forests. The first is the amount of additional tree canopy the area needs, adjusted for building concentration and environmental characteristics like soil type. That number is multiplied by a priority index that takes into account seven variables related to resident age, employment, health, income, language, race and heat severity. A higher priority index reflects a greater potential for residents to be disproportionately affected by extreme heat and environmental hazards.
Another key feature of the analyzer is its scenario tool, which allows users to see the impacts that planting a chosen number of trees would have. It provides estimates for how much carbon, water and air pollution would be sequestered, plus the economic benefit and jobs creation that those trees would provide.
“I really see this being a great tool to assist with getting funding,” said Drue Epping, the Pacific Northwest and West Coast director at American Forests.
At the local level
Zooming out on the dashboard, low tree equity scores continue from South King County down for miles along the industrial Interstate 5 corridor. Tacoma, for example, has an average score of 77, nearly 10 points lower than Seattle.
Part of the reason why is because of Tacoma’s roots as a logging town, said Tacoma Urban Forest Program manager Mike Carey.
But policy also plays a big role. Until the recent rezoning project Home in Tacoma, the city had very few laws protecting urban trees, said Robb Krehbiel, an environmental planner and Tacoma resident who volunteers on the city’s planning commission. The project implemented some tree planting requirements for developers working on private property, but the City Council is still discussing broader tree protection guidelines for Tacoma.
Balancing tree canopy needs with development is a tricky design problem, especially as cities across Washington struggle with a housing crisis.
Local nonprofits like the Tacoma Tree Foundation work closely with the city to improve its tree canopy by doing community outreach, hosting planting days and giving away trees for free.
“It can’t just be a top-down decision from cities, because the work involved in caring for the urban forest is so vast and extends to all of our properties,” Wyse said.
In 2019, Krehbiel bought a home in South Tacoma, a region with some of the lowest tree equity scores in the city. He has since planted two Garry oak trees in his yard, naming them Oak Henry and Oakphilia as literary puns.
For the past three years, Krehbiel has volunteered with the Tacoma Tree Foundation, helping plant trees in people’s yards and showing them how to care for them.
“It makes me feel more optimistic about the future when I see people get really excited to put this, this big living creature in their yard and take care of it,” Krehbiel said, “and know that it’s going to take care of us someday.”
