Interactions of socioeconomic patterns with vegetation cover and biodiversity in Los Angeles, CA

Background/Question/Methods Vegetation cover and tree biodiversity in urban ecosystems provide multiple ecosystem services for city residents, such as climate regulation and air purification. In large cities such as Los Angeles, we hypothesize that benefits may be disproportionately represented in high income areas due to the “luxury” effect. Interactions of socioeconomic patterns with vegetation in urban ecosystems are expressed spatially, reflecting human, climate, and topographic effects. Our study addresses this complex issue by combining field data with spatial and laboratory analysis. Within the boundaries of the City of Los Angeles, 151 11.2 meter plots were selected using a randomized design stratified for land use classes. Each plot was assessed for tree species, percent tree cover, and ground cover type. Trees were measured for DBH, height, crown dieback, and canopy size. Leaves were collected from each tree and measured for Specific Leaf Area (SLA) and percent carbon and nitrogen. Plot characteristics and location were organized within a Geographical Information Systems map and overlaid with socioeconomic, topographic, and climatic factors. Our analysis focused on three distinct city regions: Hollywood/Santa Monica Hills, San Fernando Valley, and Downtown (LA City Proper), which respectively contain areas with the highest, median, and lowest income census tracts. Results/Conclusions We found 364 individual trees, 96 different tree species and a surprisingly even composition of species across all of Los Angeles. The tree species with the broadest spatial distribution were commonly planted street trees. The coefficient of variation for SLA in the top five most common trees was (with the exception of Magnolia grandiflora) between 50-150% higher than trees found in only one or two plots. Despite this finding, carbon to nitrogen ratios did not vary spatially within common tree species. Plots in census tracts with income above $50,708/year (median income for Los Angeles) had four to five times more trees, twice as much tree cover, and less impervious ground cover compared with corresponding low income (below $20,000/year) areas. Treeless plots. while occurring in every income bracket, were twice as common in low income census tracts. These results were mirrored in our regional study, with Hollywood, San Fernando Valley, and Downtown sites ranked proportionally from high to low in income, number of trees, and tree cover. Our results show income to be a driving factor in the spatial distribution of tree and ground cover in metropolitan areas.