Print PageIn the northeast, the average life span for an urban street tree is estimated to be only 10 years, with a 50% mortality rate in the first year of growth. The increased environmental pressure associated with anthropogenically dominated environments has been well documented. In general, trees in urban environments are exposed to increased pollution, water stress, inadequate soil conditions, heat island effects, and numerous other factors that may directly limit their growth and vitality. However, at a local-scale the interaction between environmental and socioeconomic factors may also influence survival resulting in locally unique patterns of mortality that may be lost to large-scale aggregation. The goal of this study was to determine whether such interactions help explain tree mortality in the Washington D.C. area. A spatial analysis of tree mortality was conducted using a Ripley’s K function. Following this analysis, U.S. Census Bureau data was used to assess mortality rates among census tracts. An index of seven factors, including median income, population density, percent of population under 25 years of age, median rent, median value of house, percent unemployment, and percent with at least a high school Diploma were used to assess the association between socioeconomic and urban tree mortality.
Results/Conclusions
The Ripley’s function, which uses nearest-neighbor distances to determine spatial pattern, revealed an aggregated distribution associated with tree mortality. A series of chi-square tests revealed a strong association between urban tree mortality and six socioeconomic factors. Income was determined to be the best predictor of tree mortality, with a p-value of <0.0001 across all factor level comparisons. Population density was the only factor that did not show a clear association with tree mortality. The results of this study help to highlight gaps associated with scale and areas of further research that are important to the success and re-establishment of many urban forests.
