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The Tree Equity Score

Research has shown that trees play a vital role in promoting well-being. Spending time in nature, such as hiking or forest bathing, has several positive effects on a person's physical, mental, and spiritual health. Trees can promote these benefits at the community level too. However, communities without sufficient tree coverage miss out on the numerous health and environmental services that trees offer. Unfortunately, certain communities and individuals, particularly those residing in urban areas, have reduced access to the tree canopy compared to others. Therefore, the need for adequate tree coverage is a matter of social and environmental justice for all.


Benefits That Trees Provide


Trees Promote Health


Trees influence the local climate. In a previous post, we touched on the importance of trees in helping cities reduce heat trapped by the urban infrastructure. Trees have a real impact on our physical health because without urban forests, high temperatures pose a much greater threat to the community’s health and thermal comfort. An urban canopy can also help reduce exposure to air pollution and UV radiation, and in some cases, it may reduce risks of respiratory illness.


Green spaces impact our mental health as much as our physical health. Urban trees have been linked to stronger stress recovery compared to treeless streetscapes. Green spaces in general have been shown to boost cognitive performance and mood, increase gratitude, enhance one’s attention span, and inspire better life management.


Trees give us a sense of security. They have been associated with reduced crime and increased property values. Plus they add visual appeal to spaces. Feelings of safety and satisfaction are important contributions to the community and personal well-being (Wolf et. al., 2020).


Trees Enhance the Urban Environment


Urban forests are essential in cities because of the ecosystem services provide. They can regulate climate which is important in cities that suffer high temperatures from heat islands. An urban forest can be a vital tool for reducing heat-related illness in city communities. Cities experience smog and high air pollution; trees purify the air. Impervious surfaces, which are abundant in cities, can lead to high quantities of polluted water. High-density areas developed near water can experience widespread damage from flooding. An urban forest can purify water and reduce stormwater runoff (Nowak et. al., 2008). Urban forests have numerous environmental services that benefit community integrity and health.



 

The Need For Equal Access To Trees


All in all, trees are vital to human health. In cities where tree coverage is often limited, the existing infrastructure can make it difficult to increase tree coverage and green spaces. As a result, communities living in urban environments are disproportionately harmed by a lack of trees. More specifically, high-density regions that are often occupied by low-income communities and communities of color. These communities bear more environmental harm, such as excessive heat and high pollution, than neighborhoods with better tree cover.


In the 1950’s, the Home Owner’s Loan Corporation dictated who could access certain real estate and where. They classified different regions of a city by its livability. Class D areas, which were colored red on maps, were considered unlivable and hazardous. Housing in these areas was reserved for low-income, minority, and immigrant groups. These groups were prevented from loaning houses in Class A districts. Class A areas, mapped with green, had the most desirable housing which was reserved for wealthy, native-born white people.


Though redlining has been outlawed, oppressive systems of the past continue to create unfair environmental burdens for disadvantaged people. Once-redlined communities remain some of the poorest today and still suffer from the remaining infrastructure they are forced to live around. People in these areas suffer from greater heat island effects, higher impervious surface cover, and lower tree cover (Nowak et. al., 2022). Several studies show that neighborhoods that were once red-lined, predominately affecting African-American communities, experience hotter temperatures than non-red-lined neighborhoods. In Washington D.C., neighborhoods with subsidized housing, home to some of the most financially vulnerable residents, were found to be poorly adapted to extreme heat (Leets et. al., 2022). In many American cities, the poorest neighborhoods are associated with the highest temperatures as well as the lowest tree cover.



An old map of a redlined Philadelphia. Image sourced from The Society Pages.


Studies show that urban tree canopies have a strong positive correlation with median household income. In the Bronx, disadvantaged socio-demographic and socio-economic groups experienced disproportionately lower tree cover (Charity and Charles, 2020). One study examining large cities found that in neighborhoods once classified as Class A areas, tree cover averaged around 40.1% while previous Class D areas averaged 20.8%. As a result, disadvantaged communities receive unequal and inequitable access to urban canopy ecosystem services. In some cities, the tree cover disparity in once-redlined areas equates to losses of millions of dollars in ecosystem benefits (Nowak et. al., 2022).




A map of tree canopy cover in Philadelphia as of 2018. Map from the Philly Tree Plan. Compare this map to the old redlining map above to visualize tree canopy cover relative to regions of redlining.


Areas with little tree cover in disadvantaged communities must be the priority for expanding the urban canopy. The expansion of the tree canopy in these communities needs to be equitable, not just equal. Luckily, there is a tool to help identify just where those priorities should be.


 

The Tree Equity Score


The relationship between tree cover in urban spaces and community health, based on various socioeconomic and sociodemographic conditions, can be linked using a Tree Equity Score. This tool, created by American Forests, rates a geographical area for its tree cover disparity. Factors that are evaluated for this score consider a region’s building density, the percentage of tree cover, and surface temperature. It also considers factors like unemployment, the percentage of people living in poverty, the percentage of children and seniors, the percentage of people of color, linguistic isolation, health burden index, and heat disparity.


Trees provide many benefits, like cooling local air temperatures, purifying the water and air, reducing stormwater, and more. The tree equity score assesses if the benefits from the surrounding tree cover are reaching the communities that need those benefits the most. Scores range from 0 to 100. A low score indicates that a community is disproportionately harmed by lacking tree-based benefits compared to areas with higher scores. A low-scoring community is thus in greater need of trees to offset unfair environmental burdens, like high heat and exposure to air pollution.


The factors used to calculate a tree score.

An example of a high-priority region with a lower tree equity score. Sourced from West Chester.


A snapshot of Philadelphia using the tree equity score. Orange blocks have the lowest scores while bright green blocks have the highest scores.


The goal of a tree equity score is to highlight areas where efforts for investing in an urban tree canopy should be directed to best uplift the community. While the score is useful for directing efforts toward areas that need the most attention, this is only the first step. Real, intentional action is needed to address tree cover disparity and foster change. Some cities have integrated the tool into their tree plans to target areas of need. The tree equity score is free to the public for use. To see how your neighborhood fares, visit www.treeequityscore.org. This tool could be the first step to building a better and more resilient community.

 

References


Charity N. and Charles N. K. 2020. The equity of urban forest ecosystem services and benefits in the Bronx, NY. Urban Forestry & Urban Greening. Volume 53. https://doi.org/10.1016/j.ufug.2020.126723.


Leets, L., Sprenger, A., Hartman, R. O., Jackson, J. H., Britt, M., Gulley, A., Thomas, J. S., and Wijesinghe, S. 2022. Promoting tree equity in Washington, D.C. Trees, Forests and People. Volume 7. https://doi.org/10.1016/j.tfp.2022.100209.


Nowak, D. J., Crane, D. E., Stevens, J. C., Hoehn, R. E., Walton, J. T. and Bond, J. 2008. A ground-based method of assessing urban forest structure and ecosystem services. Arboriculture & Urban Forestry. Volume 34(6): 347-358.


Nowak, D. J., Ellis, A., and Greenfield, E. J. 2022. The disparity in tree cover and ecosystem service values among redlining classes in the United States. Landscape and Urban Planning. Volume 221. https://doi.org/10.1016/j.landurbplan.2022.104370.


Wolf, K. L., Lam, S. T., McKeen, J. K., Richardson, G. R. A., van den Bosch, M., and Bardekjian, A. C. 2020. Urban Trees and Human Health: A Scoping Review. International Journal of Environmental Research and Public Health. Volume 17(12):4371. https://doi.org/10.3390/ijerph17124371


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