Trees provide critical ecosystem services to people who live in cities, such as local cooling, air purification, and runoff reduction. It has long been appreciated that trees in cities are under threat from stressors associated with both urbanization and climate change. What is not known, however, is the extent to which tree species currently planted within urban areas will continue providing ecosystem services as the climate warms, water becomes more limited, and urbanization intensifies. We propose to apply an experimental framework that harnesses existing urban heat gradients as analogs of future climate conditions to infer how climate change could affect local cooling services provided by popular and commercially-important urban trees species. For tree species that experience a wide range of urban temperatures, we will assess key metrics describing their capacities to reduce local temperatures, including various metrics of growth and shade quality. This work will provide a blueprint for determining how escalating heat stress may affect the equity of ecosystem services provided by urban trees across US cities. To expand this work beyond our focal cities, we propose to survey key actors in the supply chain for urban trees (tree growers, developers, arborists) to determine how they make decisions about which tree species to plant and, importantly, to what extent climate change, ecosystem services, and socioeconomic factors play into these decisions. This project represents a critical first step toward building urban forests that will continue to provide ecosystem services under future climates.
