Cities are investing in programs to expand tree cover and the myriad of benefits trees provide, such as cleaner and cooler air. In the first citywide health impact assessment of the estimated effects of a tree canopy initiative on premature mortality, a Northern Research Station scientist and her partners found that tree cover in Philadelphia could also reduce premature deaths.

In Philadelphia, tree canopy ranges from 2 percent to 88 percent, with an average 20 percent urban tree canopy coverage based on 2014 data. A research team that included the Northern Research Station and universities examined the potential impact on human mortality from Greenworks Philadelphia, a plan to increase tree canopy to 30 percent across the city by 2025. The analysis is one of the first to estimate the number of preventable deaths based on exposure to greenspaces and potential mechanisms such as increased physical activity, or reduced air pollution, noise, heat, and crime using a tool developed by public health researchers in Spain and Switzerland called Greenspace-Health Impact Assessment. Researchers found that increased tree canopy could prevent between 271 and 400 premature deaths per year in Philadelphia, suggesting that increased tree canopy or green space could decrease morbidity and mortality for urban populations, particularly in areas with lower socioeconomic status where existing tree canopies tend to be the lowest.