Tree canopy equity: how Tree Equity Score and a seven-city study measure it

This page reports what the named sources say. It takes no side on how cities should spend on trees. Related pages are trees and urban heat and urban forestry programmes.

Tree Equity Score as American Forests defines it

American Forests, a nonprofit, publishes Tree Equity Score. Its home page describes the score as a single measure from 0 to 100 that combines information from a variety of sources, and says the lower the score, the greater the need for investment. The inputs it lists are tree canopy, building density, income and employment, race, surface temperature, health, language and age. It says the score was created to guide investment toward communities living on low incomes, communities of color and people disproportionately affected by extreme heat, pollution and other environmental hazards.

The organization's About page says scores are available for nearly 200,000 urban neighborhoods in the United States, covering more than 260 million people. It also states that over 500 million more new trees are needed to reach Tree Equity in all areas with inadequate tree cover. That is American Forests' own estimate. The site offers a National Explorer map, and local Analyzers for named cities and regions that support planting plans at property level. The methodology page, which holds the formulas, loads its text with scripts, so this page does not report weights or thresholds from it.

The seven-city study

Schwarz and colleagues published Trees Grow on Money: urban tree canopy cover and environmental justice in PLoS ONE on April 1, 2015. They examined urban tree canopy cover in Baltimore, Los Angeles, New York, Philadelphia, Raleigh, Sacramento and Washington, D.C., using high-resolution land cover data and census data analyzed at the census block group level with correlation, regression and a spatial regression model.

Question	What the authors report
Tree canopy and income	Across all seven cities there is a strong positive correlation between canopy cover and median household income.
Tree canopy and race	Negative correlations between race and canopy exist in bivariate models for some cities, but are generally not observed in multivariate regressions that add income, education and housing age.
Where the expected pattern appeared	The conclusion says low canopy in neighbourhoods with a high share of racial and ethnic minorities appeared only in the California cities of Sacramento and Los Angeles. The authors suggest aridity and dependence on irrigation may amplify socioeconomic differences there.
Method note	Spatial regression models fit better than ordinary least squares in every city, which the authors take to mean spatial autocorrelation matters.

The authors write that a suite of variables, including income, contributes to how canopy is distributed, and say the findings could help target canopy goals and environmental justice concerns together. They list further work they call needed: analyses of the costs and benefits of keeping tree cover in arid and humid places, and qualitative work on how residents manage their land.

The Forest Service programme

The U.S. Forest Service describes its Urban and Community Forestry Program as the only federal programme dedicated to growing and maintaining urban and community trees, forests and green spaces, serving places where it says 84 percent of Americans live, work and play. Its page does not define a canopy equity measure.

Reading the two together

The two sources do different jobs. Tree Equity Score is a published index built by a nonprofit, with race as one of its inputs. The 2015 study is a peer-reviewed analysis of seven cities in which race did not hold up in most multivariate models. The two are not tests of each other.