Collaborative Research: Impacts of Dynamic, Climate-Driven Water Availability on Tree Water Use and Health in Mediterranean Riparian Forests

由于气候驱动的树木可用水变化，河流沿线的森林受到威胁。当根区的水分有限时，树木会经历影响其整体生长和健康的生理变化。这个问题在夏季温暖、干燥的地区(例如美国的大片地区)的河流泛滥平原的森林中尤为严重。这种森林提供一系列生态系统服务，但它们在面积、物种多样性方面有限，在不断变化的气候下进行管理具有挑战性。本项目旨在建立对生态水文学的新认识。通过采用一套跨学科的研究方法，将水的可获得性与森林健康联系起来。它包括从河滩树木中提取树芯以调查年生长情况，并将进一步调查同位素特征？在每个年轮内记录的树木使用的源水的数量。通过监测气候变化和从各种来源收集水，该项目将深入了解森林树木潜在水源的变化。为了推广这项研究，这项研究将使用一个数字模型来评估在区域气候变化的合理情景下，气候是如何控制进入森林的水的。该项目将为森林/水/流域管理从业者提供新的工具和信息，为水文科学中代表性不足的群体提供国际教育机会，并为本科生开设一门新的生态水文学课程。这一研究项目结合了：1)实地测量气候和水文以及实验室分析所有潜在树木水源的氧同位素；(2)对一年生树木年轮中的氧和碳同位素进行当代和回顾分析，以调查最近气候驱动的树木用水量和水分利用效率的波动；(3)通过高分辨率、微切片？其中包括：(1)对树木年轮进行监测，以评估树木水源使用的季节波动；(4)改进和应用气候驱动的数值生态水文学模型，其中包括进入泛滥平原的动态水通量、同位素分馏/混合和树木吸水量。它将比较沿强烈气候梯度的森林地点的水可获得性对气候的生态水文响应。目前，将树木/森林反应与十年气候变化联系起来的能力有限。目前缺乏将区域气候与水的可获得性和跨林地的河岸树木的用水联系起来的概括性理解，这限制了森林在十年时间尺度上对干旱胁迫作出反应的预测能力。这项研究将有助于：i)确定河岸森林内水分胁迫的特征；ii)森林对气候变化反应的预测能力；iii)更清楚地描述泛滥平原水资源可获得性的区域变化；以及iv)通过在不同气候强迫条件下对水资源的供应和使用提供更好的约束，改进树枝古气候重建。这一研究项目将为管理人员提供新的视角和工具，以预测和减轻气候变化对温带和地中海气候区域主要河流沿线脆弱河岸森林资源的风险。该项目将主办一个为期两天的研讨会，向研究区域的从业者和利益攸关方传播我们的调查结果。它还包括一项本科生研究经历(REU)补充资料，使两名女性和/或少数族裔学生能够前往法国，作为她们参加第一次实地活动的第一次国际旅行。REU将为这些学生提供令人兴奋的国际研究体验、世界级的学习机会，并介绍他们在环境/水文科学领域的潜在职业。此外，这项研究的数据和模型将被纳入UCSB关于旱地生态水文学的新的高级课程。

Forests along rivers are under threat due to climate-driven changes in water availability to trees. When water in the rooting zone is limited, trees undergo physiological changes that affect their overall growth and health. This problem is particularly acute within forests in river floodplains in regions with warm, dry summers (e.g., large areas of the USA). Such forests provide a range of ecosystem services, but they are limited in area, species diversity, and are challenging to manage under a changing climate. This project aims to build new understanding of the ?ecohydrological? links between water availability and forest health by employing an interdisciplinary set of research methods. It involves extracting tree cores from floodplain trees to investigate annual growth and will further investigate the ?isotopic signatures? of source water used by trees as recorded within each annual ring. By also monitoring climate variations and collecting water from various contributing sources, the project will provide insight into variations in potential source waters to forest trees. To generalize this research, the research will employ a numerical model to assess how climate controls water access to forests under plausible scenarios of regional climate change. The project will generate: new tools and information for practitioners of forest/water/basin management, international educational opportunities for underrepresented groups in the hydrologic sciences, and a new ecohydrology course for undergraduates. This research project combines: 1) field-based measurements of climate and hydrology and laboratory analysis of oxygen isotopes from all potential tree water sources; (2) contemporary and retrospective analysis of oxygen and carbon isotopes in annual tree-rings to investigate recent climate-driven fluctuations in tree water use and water use efficiency; (3) seasonal (intra-annual) analysis of oxygen isotopes via high-resolution ?micro-slicing? of annual tree rings to assess seasonal fluctuations in tree water source use; and 4) improvement and application of a climate-driven numerical ecohydrology model that includes dynamic water fluxes into the floodplain, isotopic fractionation/mixing, and tree water uptake. It will compare the ecohydrologic responses to climate in water availability at forest sites along a strong climatic gradient. There is currently limited ability to link tree/forest response to decadal climate shifts. Generalizable understanding linking regional climate to water availability to water use by riparian trees across forests stands is currently lacking, which limits predictive capability of forest response to drought stress over decadal timescales. This research will enable: i) identification of signatures of water stress within riparian forests; ii) predictive capability of forest response to climate change; iii) a clearer picture of regional variations in the expression of climate within floodplain water availability; and iv) improvement of dendro-paleoclimate reconstructions by providing better constraints on water availability and use under different conditions of climatic forcing. This research project will provide managers with a new perspective and tools for anticipating and mitigating the risks of climate change on vulnerable riparian forest resources along major rivers in temperate and Mediterranean climatic regions. The project will host a 2-day workshop to disseminate our findings to practitioners and stakeholders in in the study region. It also includes a Research Experiences for Undergraduates (REU) supplement to enable two female and/or minority students to travel to France as their first international trip to participate on the first field campaign. The REU will provide these students will an exciting international research experience, a world-class learning opportunity, and an introduction to a potential career in environmental/hydrologic sciences. Additionally, data and models from this research will be integrated into a new upper division course on dryland ecohydrology at UCSB.