COLLABORATIVE RESEARCH: EAGER-NEON: How do Microscale Biophysical Processes Mediate Ecosystem Shifts during Climate Change-driven Drought?

森林景观因气候变化、火灾制度和土地利用以及它们之间的反馈而发生变化。影响加州的前所未有的干旱为我们提供了一个及时的自然实验，以提高我们对长期干旱影响下森林变化的认识。研究人员将利用国家生态观测站网络（NEON）的数据，与他们的小气候测量、树种建立的实验数据和生态系统模型相结合，了解森林对干旱的反应如何导致遭受干旱影响的西部地区的景观变化。了解由全球变化驱动的区域森林动态是如何被当地地形对山区气候的影响所缓和的，这一点至关重要。例如，树苗可能会在更凉爽、更湿润的朝北斜坡上躲避干旱。目前的干旱预示着21世纪气候变暖所导致的干旱条件的扩大，并提供了一个很好的机会来回答有关北美西部水资源有限的森林生态系统恢复能力的关键问题。预测能力对于预测和规划全球变化对包括流域保护在内的森林生态系统服务的影响至关重要。这项研究的结果将支持土地管理者和决策者对森林进行适应性管理，并有助于将当地维持森林生物多样性和生态系统服务的努力与区域和全球缓解计划联系起来。研究人员将检验微环境对森林动态的宏观生态模式产生强烈影响的假设。具体来说，研究问题是：1)在太平洋西南NEON域的南内华达山脉山麓和山脉的细微时空尺度上，小气候（太阳日照、地表温度和土壤湿度）是如何变化的？2)该区域内发生的亚高山气候梯度与丘陵地区局部小气候和植被冠层覆盖度变化之间的关系如何？3)干旱引起的树木死亡如何影响微环境条件，死亡模式和林隙形成如何影响随后的森林动态？NEON机载观测平台（AOP）获得的图像提供了无与伦比的数据源，支持植被组成、状况和结构的跨尺度观测，再加上适当的地面数据，将允许研究人员模拟小气候、植被、植物群落和生态系统动态之间的联系。NEON机载图像数据将用于开发基于成像光谱和机载激光扫描数据融合的细粒度森林组成和结构图。绘制的植被结构将与气候一起作为苗木建立模型的预测因子。绘制的森林组成将为景观扰动和演替的森林群落模拟模型设定初始条件，并利用全球变化情景下的幼苗建立概率进行模拟。该研究将加深我们对如何将局部尺度生物物理变化的知识纳入大尺度生态系统动力学模型的理解。该项目解决了EAGER-NEON的目标，即利用NEON数据与其他数据相结合，扩展潜在变革性研究的空间和时间维度。

Forested landscapes are transformed by changing climate, fire regimes and land use as well as feedbacks among them. The unprecedented drought affecting California provides a timely natural experiment for advancing our knowledge of forest change under the effects of prolonged drought. The investigators will leverage National Ecological Observatory Network (NEON) data in synergy with their microclimate measurements, experimental data on tree species establishment, and ecosystem models to understand how forest response to drought may lead to landscape change in the drought-stricken West. It is critical to understand how regional forest dynamics, driven by global change, are moderated by the effects of local topography on climate in mountainous landscapes. For example, tree seedlings may find refuge from drought conditions on cooler, moister north-facing slopes. The current drought foreshadows the expanding drought conditions anticipated under 21st century warming and offers an excellent opportunity to answer key questions about ecosystem resilience in water-limited forests of western North America. Predictive capability is critical for anticipating and planning for global change effects on forest ecosystem services that include watershed protection. Results form this research will support adaptive management of forests by land managers and policy makers and help bridge local efforts to maintain forest biodiversity and ecosystem services to regional and global mitigation plans.The investigators will test the hypothesis that microenvironments exert a strong influence on macroecological patterns of forest dynamics. Specifically, the research questions are: 1) How do microclimates (solar insolation, surface temperature, and soil moisture regime) vary at fine spatial and temporal scales across the southern Sierra Nevada foothills and mountains of the Pacific Southwest NEON Domain? 2) How does the relationship between local microclimate and vegetation canopy cover change across the foothills to subalpine climate gradient that occur within this region? 3) How does drought-induced tree mortality affect microenvironmental conditions, and how do patterns of mortality and canopy gap formation affect subsequent forest dynamics? Imagery acquired by the NEON Airborne Observation Platform (AOP) offers an unparalleled data source to support cross-scale observation of vegetation composition, condition, and structure that, coupled with appropriate ground data, will allow the investigators to model the connections between microclimate, vegetation, plant communities and ecosystem dynamics. NEON airborne image data will be used to develop a fine-grained map of forest composition and structure based on fusion of imaging spectroscopy and airborne laser scanning data. Mapped vegetation structure will be used as a predictor, along with climate, in seedling establishment models. Mapped forest composition will set the initial conditions for a forest community simulation model of landscape disturbance and succession, and seedling establishment probabilities under global change scenarios will be used in the simulations. The proposed research will deepen our understanding of how knowledge of local scale biophysical variation can be incorporated into models of large-scale ecosystem dynamics. This project addresses the EAGER-NEON objective of leveraging NEON data in combination with other data to extend the spatial and temporal dimensions of potentially transformative research.