Collaborative Research: RAPID: A perfect storm: will the double-impact of 2023/24 El Nino drought and forest degradation induce a local tipping-point onset in the eastern Amazon?

合作研究：RAPID：一场完美风暴：2023/24厄尔尼诺干旱和森林退化的双重影响是否会导致亚马逊东部地区出现局部临界点？

• 批准号: 2403883
• 负责人: Scott Saleska
• 金额: $ 10.38万
• 依托单位: University of Arizona
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2024
• 资助国家: 美国
• 起止时间: 2024-02-15 至 2025-01-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2403883&HistoricalAwards=false
• 关键词: Collaborative; Research; RAPID; perfect; storm

The Amazon rainforest sustains itself by recycling rainfall: trees pump water from the soil and release it from their leaves as vapor, which can be recondensed in the atmosphere and fall as rain again. The potential for drought and forest degradation to break this forest-sustaining recycling system, pushing the Amazon rainforest past a point of collapse into a degraded or even savanna state, has received much recent attention in the media and scientific literature. However, exactly how the so-called ‘tipping point’ occurs in any given forest site is unclear. This project investigates two possible causes of tipping points, both of which are predicted to become more common in the future: severe drought linked to El Niño climate conditions, and forest degradation caused by increasingly frequent strong storms and winds. This award capitalizes on a fleeting opportunity to observe how the ongoing drought, amplified by previous forest degradation, shuts down the capacity of trees to transfer water from the soil to the atmosphere, and thereby breaks the water pump that sustains rainfall recycling throughout the Amazon. The knowledge produced will help scientists predict when and how Amazon-wide tipping points might occur, which would importantly affect weather patterns, water resources, and economic stability in South America, as well as global climate. This study has broad impacts on education, through training of graduate students at public universities and through a custom-designed high school educational program that connects U.S. students with Amazon researchers and real scientific data from trees of the world’s most famous tropical forest.This study focuses on whole-forest and leaf-level observations of transpiration–the transport of water by trees from soil to atmosphere during photosynthesis–through drought and initial recovery. It tests three key hypotheses at the heart of the Amazon forest tipping-point paradigm. H1) Whole-forest drought sensitivity is heightened by the legacy of previous droughts. H1 is tested by comparing eddy-flux-tower measured 2023/24 drought response to those of previous droughts, notably the extreme El Niño of 2015/16. H2) Whole-forest drought sensitivity emerges from individual trees’ differing ecophysiological strategies for drought response. These strategies contribute to ecosystem-scale drought sensitivity and structure the tipping point onset. H2 is tested by observing responses across six dominant species, providing a foundation for individual-to-ecosystem trait-based scaling. H3) Forest drought sensitivity is heightened by disturbance-induced forest degradation. H3, widely postulated but never directly tested, explores the tipping point mechanisms relating increased drought sensitivity to altered energy balance from forest cover loss. H3 is tested by comparing tree ecohydrology and microenvironments between forest interior and large windthrow gaps. This research will provide new, hard-to-observe datasets that will allow critical tests (and subsequent improvement) of models of forest drought response and ecohydrologic tipping pointsThis 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.

亚马逊雨林通过循环降雨来维持自身：树木从土壤中抽出水，并以蒸气的形式从叶子中释放出来，这些水蒸气可以在大气中重新凝结，并再次以雨水的形式落下。干旱和森林退化可能会破坏森林的维持。回收系统将亚马逊雨林推向退化甚至稀树草原状态，最近受到媒体和科学文献的广泛关注。然而，所谓的“临界点”到底是如何在任何特定的森林地点发生的。是该奖项预测了导致临界点的两个可能原因，预计这两种原因在未来将变得更加常见：与厄尔尼诺气候条件有关的严重干旱，以及调查日益频繁的强风暴和大风引起的森林退化。这是一个转瞬即逝的机会，可以观察因之前的森林退化而加剧的持续干旱如何关闭树木将水从土壤转移到大气中的能力，从而破坏维持整个亚马逊地区降雨循环的水泵。帮助科学家预测何时以及如何亚马逊范围内的临界点可能会出现，这将严重影响南美洲的天气模式、水资源和经济稳定性以及全球气候。这项研究通过公立大学研究生的培训和通过研究对教育产生了广泛的影响。定制设计的高中教育计划，将美国学生与亚马逊研究人员以及来自世界上最著名的热带森林树木的真实科学数据联系起来。这项研究的重点是对整个森林和叶层蒸腾作用的观察，即树木通过树木输送水的过程。土壤到大气光合作用——通过干旱和初始恢复。它测试了亚马逊森林临界点范式的三个关键假设。H1）通过比较涡流-来测试整个森林的干旱敏感性。塔测量了 2023/24 年干旱对以往干旱的反应，特别是 2015/16 年极端厄尔尼诺现象。这些有助于制定生态系统规模的干旱敏感性策略，并通过观察六个主要物种的响应来测试临界点的发生，为基于个体到生态系统特征的缩放提供基础。 H3 被广泛假设但从未直接测试过，它通过比较森林内部和大面积的树木生态水文学和微环境来探索干旱敏感性增加与森林覆盖损失改变的能量平衡之间的临界点机制。风投这项研究将提供新的、难以观察的数据集，以便对森林干旱响应和生态水文临界点模型进行关键测试（以及随后的改进）。该研究是法定任务，并被认为值得通过使用基金会的知识进行评估来支持。优点和更广泛的影响审查标准。