Changes in the health-related ecosystem services and disservices provided by urban trees over multiple decades in a small city

The effects of urban trees on public health should change over decades due to shifts in tree composition and abundance, environmental conditions, human demography, and disease incidence. However, there are few case studies documenting changes in the health-related ecosystem services and disservices provided by trees over time. Here we use seven tree censuses to quantify changes in the effects of city-owned trees on air pollution, allergenic pollen, hydrology, and heat due to shifts in tree abundance and environmental conditions in Ithaca, New York, a small city in the Northeastern United States. We also review how shifts in disease incidence have affected these trees’ health consequences. From 2005 to 2021, trees removed 20% more ozone and 268% more PM_2.5; they also removed substantially more runoff and had higher cooling capacity. In contrast, the amount of certain air pollutants removed by trees dropped from 2005 to 2021 for sulfur dioxide (361 kg/yr to 8 kg/yr), carbon monoxide (65 kg/yr to 32 kg/yr), and nitrogen dioxide (380 kg/yr to 298 kg/yr) as their ambient concentrations dropped. Pollen production by street trees from 1947 to 2021 initially dropped due to Dutch elm disease but has quadrupled since the 1980s due to increases in several high-pollen producing genera. Overall, this study illustrates how the public health effects of trees vary over decades due to changes in tree composition and abundance, environmental conditions, and changes in disease incidence and human demography, emphasizing the importance of incorporating long-term perspectives into contemporary tree management decisions.