The relationships between an historic neighborhood classification grade and tree canopy and impervious surface in Washington, DC, USA

Abstract

Urban tree canopy provides benefits, but is not equitably distributed across neighborhoods, which is an environmental distributive injustice. Trees take time to grow, so historic neighborhood conditions explain, in part, present-day conditions and the inequitable distribution of tree canopy and associated benefits. In 1934, the Federal Housing Administration (FHA) was created to help develop new housing and promote homeownership by insuring home loans, and consequently helped shape urban development. In 1937, the FHA ranked neighborhoods in Washington, DC, and the greater metropolitan area based on various neighborhood characteristics, including the racial composition of inhabitants, using the letters A through H. A-E areas were associated with white residents. From 1934–1962, nearly all (98 %) of the loans the FHA insured went to white borrowers. We asked if tree canopy cover (which provides benefits) and impervious surface cover (which is deleterious) is associated with the rank-order of the FHA’s neighborhood letter grades. High-resolution, high-accuracy land cover data from the Chesapeake Conservancy and FHA grade data from the Mapping Segregation Washington, DC project were used to examine and test these relationships with non-parametric Kruskal Wallis and Wilcoxon Rank Sum statistical tests. The percentage of tree canopy cover was significantly greater in high-ranked areas than lower, and impervious surface cover was more abundant in lower-ranked areas. The significant relationships persisted in sensitivity analyses using more encompassing definitions of tree canopy cover and impervious surface. The findings suggest that today’s inequitably distributed tree canopy cover is related to historic inequality.