Trees benefit human health by counteracting negative environmental outcomes like air pollution and urban heat islands. Cities across the country — including Boston, Los Angeles, and Pittsburgh — are undertaking projects to preserve and expand their tree canopies to boost positive environmental effects.

Columbus, Ohio, announced plans this fall to spend $1.45 million to increase tree canopy cover 40% by 2050, and last month Chicago announced a $46 million project to plant 75,000 trees over the next five years — especially in historically marginalized and underserved communities where tree cover is particularly low.

To determine the best and most impactful places to plant the trees, Chicago’s Department of Public Health teamed up with the University of Chicago to create a tree equity tool. The mapping and site selection tool prioritizes equity and environmental justice for the city’s tree-planting efforts.

“Taking an equity-centered and data-driven approach, we can identify where trees can have the greatest impact and work directly with residents and community groups in those areas to plant and maintain trees,” said Angela Tovar, Chicago’s chief sustainability officer, in a news release.

Bloomberg Philanthropies contributed some of the funding for the research tool pilot.

Tree tool development

The research team knew they needed a system that would integrate numerous separate data streams into one place, break down complicated geospatial insights into an easy-to-use interface, and ensure transparency. Some of the datasets include neighborhood surface temperatures, the number of asthma cases, and social vulnerability. Certain data came from NASA, and some is three-dimensional LiDAR (light detection and ranging) data collected by using a pulsating laser to measure distances.

The team built the tree equity tool using Carto’s data mapping and visualization software. Individual trees appear as dots when the user zooms in on the digital map. When zoomed out, areas displaying the darkest green color exhibit the most tree cover.

“The more you zoom in on a particular area, the more things are illuminated,” said Marynia Kolak, University of Chicago health geographer and data scientist, in a news release.

Although researchers built the tool to assist the city with its tree-planting initiative, they also created a free, open-sourced version so residents can explore environmental data in their own neighborhoods and compare it to others.

Impact

The mapping tool quantifies where trees exist citywide. It illustrates that Chicago’s historically redlined and segregated neighborhoods often contain fewer trees. These same neighborhoods often are closer to industrial areas and expressways, meaning they have higher levels of air pollution and urban heat and could most benefit from additional trees.

The tree equity tool also uncovers an area for further research: why some historically marginalized neighborhoods have maintained a high level of tree cover. For instance, Chicago’s Englewood neighborhood is one of the lowest-income areas of the city, but it has a relatively high amount of tree canopy cover. Therefore, that neighborhood is shadier and cooler during the summer than others of similar socioeconomic status.

Work on the tree equity tool emphasizes that considering multiple factors and data streams creates a more holistic technology that better solves problems. It also shows that trees can be a focal point for thinking about multiple issues in tandem, Kolak said.

“This tool is an invitation to partnerships across different groups. It can highlight disparities, but then invite folks to the table for the next stage,” Kolak said.

In addition to using data from the tree equity tool to influence its tree-planting initiative, Chicago intends to meet with local community members to hear their tree concerns. For example, some residents in underserved communities correlate more trees with gentrification and might consider tree-planting efforts a signal of unwanted development.