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

美国西南部的森林正在减少，它们的未来是不确定的。以前的许多研究都集中在野火、昆虫爆发和严重干旱等干扰是如何杀死成熟树木的。然而，在一些地方，小树也不能从种子长成成年树，这表明自然再生过程的失败也可能是重要的。温度和湿度条件的变化对幼树的生存越来越不利。这可能导致未来更严重的森林生态系统衰退。该项目将研究夏季降雨时间等短期气候事件如何支持和限制幼树的生存。当地环境的作用和幼树的抗逆性还没有得到大量的研究关注。该项目将培训本科生和研究生，包括来自代表性不足群体的个人。内华达大学拉斯维加斯分校是一所少数族裔服务机构。该项目还将通过建立三个植被和气候监测塔来加强科学基础设施。研究结果将对区域森林管理者有用，他们将获得了解美国西南部森林生态系统未来的关键信息。这项研究将使用地面现场仪器和遥感来研究引发幼树死亡事件的具体环境条件。研究区内的三种优势针叶树种：黄松、松和杜松。该仪器将在美国西南部的不同景观中部署多年。这项工作假设幼树死亡将由不同的环境条件引起，并且不像实验确定的那样严重。然而，由于幼树所处的有利小气候，很可能需要长期的环境压力才能杀死幼树。此外，在21世纪气候变化情景下，对幼树死亡机制的改进将用于加强现有的天然林更新预测。这项研究完成后，将提高我们对气候、环境和树木抗应力之间的相互作用如何影响美国西南部森林的理解。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。

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.