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

水从地面上升到树叶表面，在那里蒸发，是绿色基础设施为城市降温的重要手段。这种水的运动或蒸腾作用也与树木通过光合作用储存碳的能力有关。然而，对于不同树种如何在高温下维持蒸腾作用或叶片发育和落叶日期的变化方面对城市热量做出反应，人们还不是很清楚。因此，城市没有足够的信息来选择最能在压力条件下茁壮成长的物种，并在变暖的情况下增强气候适应能力。该项目使用无人机和卫星图像分析来观察这些反应，这种方式以前只能在实验室条件下实现。这个项目将增加我们对城市环境中的树木如何通过树木的冷却作用来帮助缓解城市变暖的理解。缺乏关于物种和种植地点（如市中心街道树、郊区公园树）如何影响城市森林蒸腾的信息，部分原因是难以在精细的空间尺度上解释城市土地覆盖的高度异质性。该项目通过使用高分辨率图像分析来解释树木对热量的响应随空间和时间的快速变化。每天将多次获得叶片温度和化学成分的无人机测量数据，以检查光合作用和蒸腾作用相互跟踪或偏离的程度。能够在一个大城市的单个树木尺度上测量树叶丰度的每周卫星图像将用于评估城市森林季节开始和结束的变化，这是对季节蒸腾的基本控制。这些分析是第一次提供观测证据，证明城市树木的功能是如何被每日和季节性增加的热量所改变的。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.