Understanding tree species response to urban heat using high resolution remote sensing

American University, Washington DC

Investigators

Abstract

Movement of water from the ground up to tree leaf surfaces, where it evaporates, is an important means by which green infrastructure cools cities. This water movement—or transpiration—is also linked to a tree’s ability to store carbon via photosynthesis. However, it is not well understood how different tree species respond to urban heat with respect to maintenance of transpiration at high temperatures or shifts in the dates of leaf development and leaf fall. Thus, cities do not have adequate information to choose the species that are best equipped to thrive under stressful conditions and bolster climate resilience under warming. This project uses drone and satellite imagery analysis to observe these responses in a manner only previously possible under laboratory conditions. This project will increase our understanding of how trees in an urban environment can help to mitigate the warming of cities though the cooling impact of trees. Information on how species and planting site (e.g., downtown street tree, suburban park tree) influence urban forest transpiration is lacking, in part because it is difficult to account for a city’s high degree of land cover heterogeneity at fine spatial scale. This project accounts for rapid changes in tree response to heat over space and time through use of high-resolution imagery analysis. Drone measurements of leaf temperature and chemistry will be acquired multiple times per day to examine the extent to which photosynthesis and transpiration track one another or diverge. Weekly satellite imagery capable of measuring leaf abundance at the individual tree scale across a large city will be used to assess changes in urban forest start and end of season, a fundamental control on seasonal transpiration. These analyses are among the first to provide observational evidence of how urban tree function may be altered by increased heat at daily and seasonal increments. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.