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

该项目填补了理解热带森林如何在从器官到树木和森林生态系统的各个尺度上应对干旱的关键空白。它将通过“科学与影响”讲习班吸引相关利益攸关方参与，在利用卫星数据的新监测能力、先进的陆地表面建模和干旱风险缓解规划方面推动扩大影响。我们建议在Amazônia上进行独特的大规模现场实验，并结合详细的生态生理学和新的基于塔的雷达测量，以在干旱期间和重要的是，在干旱后恢复期间提供跨尺度的干旱响应的新见解。水的有效性在全球碳循环中起主导作用，受到Amazônia的较大影响。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干旱，特别是热带森林中发生的生态过程的有限理解的限制。这些响应发生在不同的尺度上，从树叶到树木再到森林生态系统，对区域和全球观测到的碳循环产生非常大的影响。由于以下几个原因，了解热带森林的干旱反应具有挑战性：缺乏适当尺度的生态生理分析；有限的能力提供大规模的机械信息水压力反应的连续监测，例如使用卫星；对包括干旱胁迫及其后果在内的生态过程的理解有限。我们的问题是：干旱胁迫如何影响整个树的功能，以及热带森林干旱后蒸腾和生长等关键过程能否恢复？干旱压力是否通过限制生长潜力和增加未来干旱可能导致树木死亡的风险而留下长期遗产？关键的是，干旱对树木功能的影响如何影响许多树木的性能，即热带森林的性能？需要多尺度测量来解决这些问题。集中的生态生理测量与新的塔式雷达（微波）观测相结合，有可能在理解方面取得重大进展，从树木扩展到森林和区域。这个项目将把世界上唯一一个在热带森林进行的公顷规模的长期干旱试验与新的雷达传感器结合起来，我们已经进行了20年。我们将使用基于塔架的雷达测量来检测实验尺度下植被含水量的变化。这将提供比以前使用卫星雷达更高的分辨率检测和机制洞察，并使我们能够将雷达和植物生态生理数据连接起来。我们的具体假设涉及：器官、树木和生态系统尺度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的理解以及对功能和生存的风险；以及如何利用这种认识来推进对干旱影响的卫星监测及其更广泛的应用。总之，我们有三个主要目标：i)利用我们在Amazônian森林的生态系统尺度的干旱实验，利用植物生理学和基于塔的雷达（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和监测恢复过程，以及对生长和生存的结果，了解干旱后对森林恢复力的遗留影响。（三）利用（一）和（二）提高热带森林的大规模卫星探测能力，以改进生物量和干旱反应监测。我们将领导两个“科学与影响”研讨会，通过帮助利用植被模型改进陆地-大气相互作用的预测，以及提高土地利用规划的预警能力，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.