NSFDEB-NERC: Understanding drought and post-drought legacy effects in tropical forest

该项目解决了在理解热带森林如何应对从器官到树木和森林生态系统的不同尺度的干旱方面的一个关键空白。它将通过举办“科学与影响”讲习班，在使用卫星数据的新的监测能力、先进的陆地表面建模和减轻干旱风险规划方面推动扩大影响，使相关利益攸关方参与进来。我们建议将阿马佐尼亚独特的大规模田间试验与详细的生态生理和新的塔基雷达测量相结合，以提供对干旱期间以及重要的干旱后恢复期间跨尺度干旱反应的新见解。水的可获得性在全球碳循环中起着主导作用，受阿马佐尼亚的影响很大。然而，我们预测水供应变化的影响的能力在很大程度上受到对应对干旱的生态过程的有限理解的限制，特别是在热带森林中。这些反应发生在不同的尺度上，从树叶到树木再到森林生态系统，对区域和全球观察到的碳循环产生了非常大的影响。事实证明，由于以下几个原因，理解热带森林的干旱反应具有挑战性：缺乏适当规模的生态生理分析；持续监测大规模、例如利用卫星的机制了解的水胁迫反应的能力有限；以及对包括干旱胁迫及其后果的生态过程的了解有限。我们问：干旱胁迫如何影响整棵树的功能，热带森林干旱后蒸腾和生长等关键过程能否恢复？干旱胁迫是否通过限制生长潜力和增加未来干旱可能导致的树木死亡风险而留下长期的遗产？关键的是，干旱对树木功能的影响如何影响许多树木的表现，即热带森林的表现？为了解决这些问题，需要进行多尺度测量。将有重点的生态生理测量与新的塔基雷达(微波)观测相结合，有可能在理解、从树木到森林和区域的尺度上取得重大进展。这个项目将把世界上唯一一个在热带森林中进行了20年的长期干旱实验与新的雷达传感器结合起来。我们将使用基于塔的雷达测量来检测实验范围内植被水分的变化。这将提供比以前使用卫星雷达更高的分辨率检测和机械洞察，并允许我们连接雷达和植物生态生理数据。我们的具体假设涉及：器官、树木和生态系统对干旱和干旱后的反应之间的联系；这些数据如何促进我们对森林功能以及对功能和生存的风险的理解；总而言之，我们有三个主要目标：i)利用我们在阿马佐尼亚森林的生态系统规模干旱实验，利用植物生理学和塔基雷达(微波)测量，在多个尺度上量化和了解干旱的影响。ii)通过使用我们的实验实现的控制来停止干旱并监测恢复过程，了解干旱后对森林复原力的影响。(3)利用(I)和(Ii)推进热带森林的大规模卫星探测能力，以改善生物量和干旱反应监测。我们将领导两个“科学和影响”研讨会，通过帮助改进使用植被模型对陆地-大气相互作用的预测，以及更好的土地利用规划预警能力，迅速扩大工作成果。

This project addresses a key gap in understanding how tropical forests respond to drought across scales, from organ to tree and forest ecosystem. It will drive extended impact in new monitoring capability using satellite data, in advanced land surface modelling, and in drought risk mitigation planning, by engaging related stakeholders through 'Science & Impact' workshops. We propose the powerful combination of a unique large-scale field experiment in Amazônia together with detailed ecophysiological and new tower-based radar measurements to deliver new insights into drought responses across scales, both during drought, and importantly, during post-drought recovery. Water availability plays a dominant role in the global carbon cycle, with a large influence from Amazônia. However, our ability to predict the effects of changing water availability is substantially constrained by limited understanding of the ecological processes occurring in response to drought, particularly in tropical forests. These responses occur across different scales, from leaf to tree to forest ecosystem, with very large impacts on the carbon cycle observed regionally and globally. Understanding drought responses of tropical forests has proved challenging for several reasons: a lack of ecophysiological analysis at the right scales; limited capacity to deliver continuous monitoring of mechanistically-informed water stress responses at large scale, eg using satellites; and limited understanding of the ecological processes comprising drought stress and its consequences. We ask: How does drought stress affect whole-tree function, and can critical processes such as transpiration and growth recover after drought in tropical forests? Does drought stress leave a long-term legacy by limiting growth potential and by increasing the risk of possible tree mortality from future drought? And critically, how do the effects of drought on tree function affect performance at the scale of many trees, ie, that of a tropical forest? Multi-scale measurements are needed to address these questions. A combination of focused ecophysiological measurement with new tower-based radar (microwave) observations has the potential to enable large advances in understanding, scaling from tree to forest and region. This project will combine the world's only long-term drought experiment at hectare scale in tropical forest, which we have run for the past twenty years, with new radar sensors. We will use tower-based radar measurements to detect changes in vegetation water content at the scale of the experiment. This will provide higher resolution detection and mechanistic insight than was previously possible using satellite radars, and allow us to connect radar and plant ecophysiological data. Our specific hypotheses address: the links between organ-, tree- and ecosystem-scale responses to drought, and after drought; how these data advance our understanding of forest function and the risk to function and survival; and how this understanding can be used to advance satellite monitoring of drought impacts, and its wider use.In summary, we have three main goals:i) To use our ecosystem-scale drought experiment in Amazônian forest to quantify and understand the effects of drought at multiple scales, using plant physiology and tower-based radar (microwave) measurements.ii) To understand post-drought legacy effects on forest resilience by using the control enabled by our experiment to halt the drought and monitor recovery processes, and the outcomes for growth and survival.iii) To use (i) and (ii) to advance large-scale satellite detection capability in tropical forests for improved biomass and drought-response monitoring. We will lead two 'Science and Impact' workshops to rapidly multiply outcomes of the work by helping to improve prediction of land-atmosphere interactions using vegetation models, and better early-warning capability for land-use planning.