CAREER: A network-oriented research and education plan to explore links between forest cover and temperature in the eastern United States

在过去的一个世纪里，地球表面的大部分地区都在变暖，而在美国东部的大部分地区，气温没有上升，甚至有所下降。与此同时，由于放弃质量差的农业用地，该地区的森林覆盖率急剧增加。这个项目将检验一个假设，即美国东部的重新造林提供了解释，因为它以导致冷却的方式影响地表能量平衡，从而掩盖气候变化造成的长期变暖。就像人体通过出汗或风扇降温一样，与它们所取代的农田和草原相比，森林可能通过更高的蒸散速率和由风驱动的热能运动来降温。展望未来，随着可用空间的填满，重新造林的速度将随着时间的推移而下降，但自然填满或种植的树木类型可能会发生变化。值得注意的是，耐旱的橡树目前正在减少，而对干旱敏感的枫树和松树正在激增。因此，这项工作也将测试第二个假设，即树种的持续区域变化促进了蒸散量的减少，特别是在干旱时期，这将使地表变暖。这项研究将为可持续农业生态系统管理战略的制定提供信息，减轻干旱对生态系统生产力和功能的破坏性影响。将开发一系列讲习班，以及一个公民科学计划，旨在培训青年科学家利用和分析网络数据的有效方法。这项研究将通过与一系列环境观测网络的相互作用得以实现，这些网络汇集了来自许多生态系统的气象和生态观测，从而使环境科学的大数据方法成为可能。项目成果与正在进行的模拟工作有关，这些模拟工作旨在重现历史气候趋势并更有信心地预测未来条件。这项工作将通过生成丰富的树叶到生态系统尺度的观测数据集来推进网络驱动的环境科学，这些观测数据将与现有网络共享。这项研究的动机是认识到，在研究区域内，正在进行的管理活动正在推动从以各向异性物种为主的森林向以等水物种为主的森林过渡。等水的概念近年来受到了广泛的关注，本项目将通过对美国东部重要物种沿着等水-各向异性连续体进行分类，并建立一个包含等水-各向异性框架的气孔导度模型来推进这一知识体系。虽然该项目侧重于生态系统能量平衡，但项目成果也将有助于了解区域碳和水循环，并有助于制定森林管理战略，减轻干旱对生态系统功能的有害影响

While the vast majority of the surface of the earth has warmed over the past century, in much of the eastern United States the air temperature has failed to rise or has even declined. At the same time, forest cover over the region has increased dramatically, driven by abandonment of poor quality agricultural lands. This project will test the hypothesis that reforestation in the eastern U.S. provides the explanation, in that it affects the surface energy balance in ways that lead to cooling and thus obscures long-term warming from climate change. Just as human bodies are cooled by sweating or by a fan, forests may be cooled by greater rates of evapotranspiration and wind-driven movement of heat energy when compared to the croplands and grasslands they have replaced. Looking forward, the rate of reforestation will decline over time as available space is filled, but the types of trees that fill in naturally or are planted will likely change. Notably, drought-tolerant oaks are currently declining, while drought-sensitive maples and pines are proliferating. So this work will also test a second hypothesis that ongoing regional shifts in tree species promote a reduction in evapotranspiration, particularly during periods of drought, that will tend to warm the surface. The research will inform the development of sustainable agro-ecosystem management strategies that mitigate damaging effects of drought on ecosystem productivity and function. A series of workshops will be developed, along with a citizen science program aimed at training young scientists in effective approaches for leveraging and analyzing network data.The research will be enabled by interactions with a range of environmental observation networks, which aggregate meteorological and ecological observations from many ecosystems and thereby enable a big data approach to environmental science. Project outcomes are relevant to ongoing modelling efforts to reproduce historic climate trends and predict future conditions with more confidence. This work will advance network-driven environmental science by generating a rich collection of leaf- to ecosystem scale observations that will be shared with existing networks. The research is motivated by the recognition that, within the study region, ongoing management activities are driving a transition from forests dominated by species that are more anisohydric in their water use to forests dominated by more isohydric species. The concept of isohydry has received much attention in recent years, and this project will advance this body of knowledge by classifying important eastern U.S. species along the isohydric-anisohydric continuum, and developing a model for stomatal conductance that incorporates the isohydric-anisohydric framework. While this project is focused on ecosystem energy balance, the project outcomes will also be relevant for efforts to understand regional carbon and water cycling, and for the development of forest management strategies that mitigate deleterious effects of drought on ecosystem functioning