In 2021, when the nonprofit AZ Sustainability Alliance (AZSA) set its sights on planting trees at a school in a Phoenix-area neighborhood as part of its urban forestry program, the question was: Where? Which school around Phoenix needed trees the most?

In past years, the answer to that question may have come from AZSA staff members’ networks — who did they know working at schools and which of those schools needed trees? But this time, the group had a new tool at its disposal: Tree Equity Score (TES).

The first-of-its-kind tool uses data on population density, income, temperature, race, and tree canopy to generate a score that indicates how close a neighborhood is to having enough trees. Suddenly, the job became much easier — and more data driven.

“We would have looked to other maps and data, but once I started looking at the TES map, I said, ‘Oh my gosh, this is awesome. This is just what we need,’” says Julia Colbert, who led the project at AZSA. (Colbert now works for the Sustainable Cities Network at Arizona State University.)

Using the TES tool, AZSA easily identified an area in the town of El Mirage that was most in-need and targeted Thompson Ranch Elementary as the worthiest recipient of the planting. “To try to do this without TES would have been me emailing the 150 teachers that I know saying, ‘Hey, can your school use trees?’” Colbert says.

Colbert then approached the school’s principal armed with a data-based case for planting about 50 trees there. AZSA received a warm reception that bolsters the case for democratizing scientific data.

THE TREE EQUITY SCORE was developed in 2021 by the Washington DC-based American Forests, one of the oldest conservation nonprofits in the country.

“This data is provided to help you make the case for planting trees in the right places,” says Chris David, vice president of GIS and data science at American Forests and the creator of the TES program. “That is what democratizing data means: to make it easy for anyone to use data to make decisions.”

So far, the tool provides a score to measure tree canopy in 150,000 neighborhoods in hundreds of metropolitan areas in the U.S. American Forests is expanding TES’s reach to rural areas, as well as Puerto Rico, Hawai’i, and Alaska. An international pilot is also in the works. The TES tool is free and accessible to the public via the Tree Equity Score National Explorer, which allows limited filtering and scenario analysis for users to see the effects of planting trees in particular places.

American Forests is also working on a Tree Equity Score Analyzer (TESA), another publicly available tool that allows for a deeper dive into the data and greater customization of planting scenarios. TESA users can simulate custom scenarios and analyze the estimated benefits of tree-planting down to the parcel level.

While American Forests coined the term “tree equity” and spurred the broader movement to address this issue, the idea that tree cover should be equitably distributed among neighborhoods of course predates the organization’s efforts on this front. Research on housing discrimination found that 94 percent of neighborhoods subject to historic redlining during 1930s have lesser tree cover and are hotter than those that hadn’t been redlined. The imbalance in tree canopy causes quality-of-life differentials among communities.

On average, socioeconomically disadvantaged US neighborhoods populated by people of color have 33 percent less tree cover than wealthier, Whiter neighborhoods. Areas with poverty rates of 90 percent or more have 41 percent less tree canopy than communities with poverty rates of 10 percent or less. That means these communities are missing out on the health, economic, and climate benefits trees provide. Neighborhoods that lack sufficient canopy suffer from more heat-related illnesses and deaths, higher utility costs, poorer air quality, and less shade than those with more trees.

The work to develop TES and TESA started about two years ago as a pilot program in Rhode Island that brought together a group of stakeholders — municipal foresters and local nonprofits working on urban greening and forestry — to help guide the process of developing the tools that could help with equity-focused tree-planting efforts across the country.

As part of that project, American Forests gave a local nonprofit, Groundwork Rhode Island, a grant to field test the first iteration of the TES tool in 2021. Groundwork had noticed that a tree giveaway program, the Providence Neighborhood Planting Program run in partnership with the City of Providence, was unknown to many residents. The trees were disproportionately going home with wealthy White residents who had the time and resources to learn about the program. Using TESA, Groundwork was able to do targeted door-to-door canvassing to get more residents interested in planting trees on their property and to help them put in an application to receive a tree through the program.

“We want to make sure TESA can be used as an advocacy tool for folks who are most impacted by tree inequity, such as neighborhoods with high concentrations of people in poverty and people of color,” says Molly Henry, director of climate and health at American Forests. “Getting it in their hands and making sure they have the support they need to talk about these issues to decisionmakers.”

After the first TESA was completed for Rhode Island, American Forests customized the tool for other cities, including Boston, Washington DC, Austin, Dallas, Phoenix, Detroit, and Indianapolis. Other cities will follow.

In 2021, Phoenix became the first urban area to officially pledge commit to creating tree equity by 2030, a goal that includes increasing tree canopy in each of its 185 parks to 25 percent. To support this effort, Phoenix increased its funding for urban forestry by $1.6 million, and it will use the TESA to target its tree-planting efforts.

For Phoenix, the Tree Equity Score is especially helpful. A large desert city can’t rely on universal standards for tree canopy that apply for more temperate regions. TES allows the city to target trees where they’ll be most impactful.

“To increase tree canopy to 15 percent, which is the estimate we think a desert biome can support across 500 square miles, would take an enormous number of trees,” says Eric Candela, director of local government relations at American Forests. “Many of [the trees] would end up being planted in places that were providing only nominal value to people and residents of the community. They saw in the TES application a logical way that they could really address the problem in a meaningful way.”

After promising results using TES, Phoenix has now dedicated another $6 million to urban forestry. Other cities have begun their own projects. Las Vegas has committed to planting 60,000 trees on public property, using the TES to target its work. Baltimore County’s Operation ReTree is working to place more trees in high-density, lower-income areas, using a custom tree equity tool the city designed for the purpose.

Having an easier, more consistent way to make decisions on where and how to plant trees for maximum benefit is increasingly important in a world where climate change is boosting average temperatures and public health inequities are on the rise.

“Tree equity wasn’t a big topic before, and now I see other organizations and media talking about it and bringing it into the public eye,” says Henry. “That’s been fulfilling to see that this work has had an influence on the larger national conversation.”