Urban Tree Canopy Cover and Environmental Justice

This study examines the distributional equity of urban tree canopy (UTC) cover for Baltimore, MD, Los Angeles, CA, New York, NY, Philadelphia, PA, Raleigh, NC, Sacramento, CA, and Washington, D.C. using high spatial resolution land cover data and census data. Data are analyzed at the Census Block Group levels using Spearman’s correlation, ordinary least squares regression (OLS), and a spatial autoregressive model (SAR). Across all cities there is a strong positive correlation between UTC cover and median household income. Negative correlations between race and UTC cover exist in bivariate models for some cities, but they are generally not observed using multivariate  regressions that include additional variables on income, education, and housing age. SAR models result in higher r-square values compared to the OLS models across all cities, suggesting that spatial autocorrelation is an important feature of our data. Similarities among cities can be found based on shared characteristics of climate, race/ethnicity, and size. Our findings suggest that a suite of variables, including income, contribute to the distribution of UTC cover. These findings can help target simultaneous strategies for UTC goals and environmental justice concerns.

In a nutshell, this resource offers:

• Urban tree canopy coverage, income, and race distributions compared across seven major U.S. cities.
• Evidence that urban tree cover is not equally distributed with regards to income levels, and in some cases, race.
• A reflection of current vegetation patterns and social structure potentially mismatching with long-lived vegetation (i.e., trees).
• A suggestion that climate (arid versus temperate environments) may amplify the income-tree canopy disparity, since arid cities depend on irrigation to maintain tree canopy cover.

How to use this resource:

• As a peer-reviewed citation or basis for environmental justice or equity-based projects.
• To help direct city-scale sustainability, urban forestry, or planting projects.
• As background knowledge to understand the connections between income, race, and benefits or disservices provided by urban trees.
• As a source for citations regarding the benefits and possible disservices of urban trees.

Authors: 

Kirsten Schwarz, Michail Fragkias, Christopher G. Boone, Weiqi Zhou, Melissa McHale, J. Morgan Grove, Jarlath O’Neil-Dunne, Joseph P. McFadden, Geoffrey L. Buckley, Dan Childers, Laura Ogden, Stephanie Pincetl, Diane  Pataki, Ali Whitmer, Mary L. Cadenasso

Date published: 2015

Point of contact: Kirsten Schwarz, Department of Biology, Northern Kentucky University, schwarzk1@nku.edu 

Citation: Schwarz, K; Fragkias, M; Boone, C G; Zhou, W; McHale, M; Grove, J.M.; et al. 2015. Trees Grow on Money: Urban Tree Canopy Cover and Environmental Justice. PLoS ONE 10(4): e0122051.

Resource available online here.