Historical redlining is associated with disparities in wildlife biodiversity in four California cities

Abstract

Legacy effects describe the persistent, long-term impacts on an ecosystem following the removal of an abiotic or biotic feature. Redlining, a policy that codified racial segregation and disinvestment in minoritized neighborhoods, has produced legacy effects with profound impacts on urban ecosystem structure and health. These legacies have detrimentally impacted public health outcomes, socioeconomic stability, and environmental health. However, the collateral impacts of redlining on wildlife communities are uncertain. Here, we investigated whether faunal biodiversity was associated with redlining. We used home-owner loan corporation (HOLC) maps [grades A (i.e., "best" and "greenlined"), B, C, and D (i.e., "hazardous" and "redlined")] across four cities in California and contributory science data (iNaturalist) to estimate alpha and beta diversity across six clades (mammals, birds, insects, arachnids, reptiles, and amphibians) as a function of HOLC grade. We found that in greenlined neighborhoods, unique species were detected with less sampling effort, with redlined neighborhoods needing over 8,000 observations to detect the same number of unique species. Historically redlined neighborhoods had lower native and nonnative species richness compared to greenlined neighborhoods across each city, with disparities remaining at the clade level. Further, community composition (i.e., beta diversity) consistently differed among HOLC grades for all cities, including large differences in species assemblage observed between green and redlined neighborhoods. Our work spotlights the lasting effects of social injustices on the community ecology of cities, emphasizing that urban conservation and management efforts must incorporate an antiracist, justice-informed lens to improve biodiversity in urban environments.

Keywords: environmental justice; iNaturalist; legacy effects; redlining; species richness.

Fig. 1.

Greenlined neighborhoods detect more unique species with less sampling effort. Species accumulation curves for each HOLC grade across six clades. The x-axis shows the number of observations within each HOLC grade. The y-axis shows accumulated species richness. The dashed horizontal line* shows the maximum accumulated richness for grade A. The vertical lines** show the number of observations to reach grade A’s maximum accumulated richness in grade A (left vertical line) and in grade D (right vertical line). The difference in observations between redlined (i.e., grade D) and greenlined (i.e., grade A) neighborhoods is shown as a delta value. *Horizontal line: y = 964. **Vertical lines (grade A, grade D): x = 17,095; 25,445.

Fig. 2.

Redlined neighborhoods across California have lower species richness. Species richness for all species across six clades among HOLC grades for Los Angeles (Top Left), Oakland (Top Right), (C) San Diego (Bottom Left), and San Francisco (Bottom Right). Bars represent the mean, and whiskers represent 95% credible intervals. All pairwise comparisons are significant.

Fig. 3.

Clade richness is consistently lower in redlined neighborhoods. Species richness for (A) insects (top row), (B) birds (middle row), and (C) mammals (bottom row) shown among HOLC grades for each Californian city (columns). Los Angeles is on the far left, Oakland is on the middle left, San Diego is on the middle right, and San Francisco is on the far right. Bars represent the mean, and whiskers represent 95% credible intervals. All pairwise comparisons are significant. All comparisons between green- (i.e., grade A) and redlined (i.e., grade D) neighborhoods are significant. Note: for each clade, the y-axis (species richness) is subject to change.

Fig. 4.

Redlined neighborhoods differ in their species assemblage. Nonmetric multidimensional scaling (NMDS) for β-diversity (Jaccard’s metric) among HOLC grades in (A) Los Angeles, (B) Oakland, (C) San Diego, and (D) San Francisco. Each dot represents a neighborhood and ellipses encompass 95% data points. No overlap between ellipses suggests that HOLC grades have distinct beta diversity patterns and strong dissimilarity in species assemblage. Substantial overlap in ellipses suggests that beta diversity between HOLC grades is more similar to each other and there is strong similarity in species assemblage.