Investigating drought-induced forest ecosystem evolution using water use efficiency

Forest mortality from drought and heat stress has increased worldwide during the past decades, and is expected to happen more frequently as drought events become more common due to global climate change. How different forest ecosystems respond dynamically to drought events of varying severity is not well understood. As a selective force, drought could drive the evolution of forest ecosystems and thus impact forest drought resilience. In this study, I propose to examine the change of forest ecosystem carbon-water cycle during drought-induced evolution, using ecosystem water use efficiency (eWUE) as a proxy. Based on NASA datasets (e.g. forest canopy height and solar-induced chlorophyll fluorescence) and other datasets, the relationships between eWUE and a variety of potential factors will be assessed, to understand how different environmental conditions shape the forest ecosystem carbon-water cycle. I will then look at drought resilience, examining how different forest ecosystems respond to different kinds of drought events. Finally, I will analyze how forest ecosystem carbon-water cycle changes during drought phases and how mega drought may drive forest ecosystem evolution. North American forest ecosystems will be used as a testbed here. By studying how eWUE can be used as a proxy measure of evolution, the proposed investigation can advance our knowledge of how forest ecosystem adapt to drought. This study can inform decisions in forest management, enhance model development, improve our ability to assess and respond to drought events, and thus help society better adapt to the changing climate.