The role of short duration climate events in reducing natural tree regeneration in forests and woodlands of the southwestern United States

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Forests in the southwestern United States are declining and their future is uncertain. Much previous research focused on how disturbances such as wildfire, insect outbreaks, and severe drought killed mature trees. Yet, young trees are also failing to grow from seed to adulthood in some locations, suggesting that failure of the natural regeneration process may also be important. Changes in temperature and moisture conditions are becoming less favorable for juvenile tree survival. This may lead to even more severe forest ecosystem declines in the future. This project will examine how short duration climate events such as timing of summer rainfall support and limit juvenile tree survival. The role of local environments, and the stress tolerance of juvenile trees has not received substantial research attention. This project will train undergraduate and graduate students, including individuals from under-represented groups. The University of Nevada-Las Vegas is a Minority-Serving Institution. This project will also enhance scientific infrastructure by establishing three vegetation and climate monitoring towers. Research results will be useful to regional forest managers, who will gain critical information for understanding the future of forest ecosystems in the southwestern United States. This research will use ground-based field instrumentation and remote sensing to study the specific environmental conditions that initiate juvenile tree mortality events. The three dominant coniferous tree species in the region will be studied: ponderosa pine, pinon pine, and juniper. This instrumentation will be deployed over multiple years and across diverse landscapes in the southwestern U.S. This work hypothesizes that juvenile tree mortality will be caused by environmental conditions that are different and less severe than those determined experimentally. However, it is likely that prolonged environmental stress will be required to kill juvenile trees due to the favorable microclimates where they are located. Additionally, improved mechanistic insight on juvenile tree mortality will be used to enhance existing forecasts of natural forest regeneration in scenarios of 21st century climate change. When completed, this research will improve our understanding of how the interaction of climate, environment, and tree stress tolerance will shape the future of forests in the southwestern U.S.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.