Groundwater-forest interactions during drought in temperate forests across scales

据估计，全世界有3万亿棵树覆盖了4200万平方公里，相当于南北美洲面积的总和。世界各地的社会都依赖森林提供水、食物、药品和林产品，以及其他娱乐、文化和审美利益。从经济上讲，热带和温带森林提供的生态系统产品和服务每年在全球范围内的总价值约为23.32万亿美元。干旱和干旱制度的变化有可能通过减少森林生长和增加植被压力和死亡率来破坏这种森林服务的提供。地下水，无论何时何地，都可以缓冲特定部分的森林，使其免受不断变化的干旱制度的影响。适应干旱对森林影响的战略需要更好地了解和预测干旱反应与地下水之间的模式、后果和反馈。本研究的总体目标是评估地下水作为一种生态系统属性，减轻干旱制度变化对温带森林的不利影响。该项目将开发一套补充性干旱探测工具，以观察和联系受地下水影响的树木和森林对干旱的反应。我们将使用模拟模型将我们的测量置于一系列场景的上下文中。这项研究将通过向包括研究人员、森林和水资源管理者以及公众在内的广泛利益相关者传播结果，帮助社会更好地应对21世纪的森林和水资源挑战。随着干旱制度的不断变化和对森林的影响，确定和评价减轻干旱压力的生态系统属性以及开发监测干旱反应的新方法至关重要。传统的方法依赖于单个树木有限的水分胁迫观测和来自粗分辨率卫星图像的林分水平植被指标。这类数据的综合削弱了物种特有的响应，也不能提供必要的数据集来揭示干旱对森林的影响在空间尺度上的联系机制。通过提议的工作，多种证据线将用于量化特定物种的树木和森林对地下水缓冲的干旱反应。具体而言，本研究建议利用：(1)树木年轮年表提供树木的历史响应，量化地下水对树木生长和干旱脆弱性的影响；(2)利用加速度计测量树摇，连续监测水分胁迫和树木对干旱的生理反应；(3)利用高光谱遥感技术绘制植物叶片干旱响应的空间图谱。这些监测干旱反应的新方法将与传统的互补数据集结合起来，开发一套模拟地下水-树木相互作用的数值模型，以机械地代表实地观测结果。该项目将为了解地下水在温带森林树木、样带和景观尺度上的抗旱作用提供基础。

An estimated 3 trillion trees cover 42 million km2 worldwide - equivalent to the combined areas of North and South America. Societies around the globe rely on forests for water supply and provision of food, medicine, and forest products, as well as other recreational, cultural, and aesthetic benefits. Economically, tropical and temperate forests provide ecosystem goods and services totaling an estimated $23.32 trillion/yr worldwide. Drought - and changes in drought regimes - have the potential to disrupt this provisioning of forest services through reduced forest growth and increased vegetation stress and mortality. Groundwater, when and where available, may buffer specific portions of forest from the consequences of changing drought regimes. Strategies to adapt to drought impacts on forests requires improved understanding and forecasting of patterns, consequences, and feedbacks between drought response and groundwater. The overarching goal of this research is to evaluate groundwater as an ecosystem attribute that alleviates adverse impacts of changing drought regimes on temperate forests. This project will develop a suite of complementary drought detection tools to observe and link tree and forest response to drought, as influenced by groundwater. We will use simulation models to place our measurements in the context of a range of scenarios. This study will help society to better address forest and water resource challenges in the 21st century through dissemination of results to a broad array of stakeholders including researchers, forest and water resource managers, and the public. As drought regimes continue to change and impact forests, it is critical to identify and evaluate ecosystem attributes that alleviate drought stress and to develop novel methodologies to monitor drought response. Traditional methods rely on limited water stress observations of individual trees and stand level vegetation metrics derived from coarse resolution satellite images. Synthesis of such data dilutes species-specific responses and does not provide the necessary datasets to reveal mechanisms linking drought impacts on forests across spatial scales. Through the proposed work, multiple lines of evidence will be used to quantify species-specific tree and forest response to drought as buffered by groundwater. Specifically, this research proposes to investigate drought response across gradients of groundwater depth using: (1) tree ring chronologies to provide historic tree response and quantify the influence of groundwater on tree growth and drought vulnerability; (2) tree sway measurements from accelerometers to continuously monitor water stress and tree physiological response to drought; and, (3) hyperspectral remote sensing to spatially map species-specific foliar drought response. These novel methods for monitoring drought response will be aggregated with traditional complementary datasets to develop a suite of numerical models for simulating groundwater-tree interactions to mechanistically represent field observations. This project will provide a basis for understanding the role of groundwater in conferring drought resistance at the tree, transect, and landscape scales in temperate forests.