Optimization of Ecosystem Services of Shanghai Urban–Suburban Street Trees Based on Low-Carbon Targets

Road traffic carbon emissions are an important cause of global warming, and street trees play an important role in regulating road carbon emissions. During urbanization, major differences in the planting management modes and growth status of the street trees in urban–suburban gradient may exist, leading to significant differences in the low-carbon values of the street trees in urban–suburban gradient. Based on this, this study took two typical urban–suburban gradient zones in Shanghai as an example to analyze the changes in the characteristics of street tree species, planting density, tree sizes, and low-carbon contribution with urban and rural changes, and proposed strategies for optimizing the low-carbon contribution of urban street trees. The results showed that, from the inner ring to the outer ring and the suburban ring, the proportion of London plane tree gradually changed from 82% to 11%, and the proportion of the camphor tree gradually changed from 9% to 70%; the average DBH of the trees gradually decreased from 28.81 to 23.74 cm. The number of plantings per unit road length gradually increased, and the number of plantings per unit area gradually decreased; therefore, the average low-carbon contribution of urban–suburban street trees is not significant, but the low-carbon contribution of upper street trees per unit area is higher, and suburban unit street trees have a higher low-carbon contribution. Finally, this article proposes different optimization strategies for future urban micro-renewal and suburban new-city construction.

Urban forest biodiversity and cardiovascular disease: Potential health benefits from California’s street trees

Enhanced immune functioning in response to biodiversity may explain potential health benefits from exposure to green space. Using unique data on urban forest biodiversity at the zip code level for California measured from 2014 to 2019 we test whether greater diversity of street trees is associated with reduced death from cardiovascular disease. We find that urban forests with greater biodiversity measured via the Shannon Index at the genus level are associated with a lower mortality rate for heart disease and stroke. Our estimates imply that increasing the Shannon Index by one standard deviation (0.64) is associated with a decrease in the mortality rate of 21.4 per 100,000 individuals for heart disease or 13% and 7.7 per 100,000 individuals for stroke or 16%. Our estimates remain robust across several sensitivity checks. A policy simulation for tree planting in Los Angeles based on our estimates suggests that if these relationships were causal, investment in planting for a more biodiverse set of street trees would be a cost-effective way to reduce mortality related to cardiovascular disease in urban areas.