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，河流沿岸的森林受到威胁。当生根区水分有限时，树木会发生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地区（如美国的大片地区）洪泛区的森林中尤为严重。这些森林提供了一系列生态系统服务，但它们的面积和物种多样性有限，并且在不断变化的气候下难以管理。该项目旨在建立对生态水文的新认识。通过采用一套跨学科的研究方法，在水资源供应与森林健康之间建立联系。它包括从洪泛区树木中提取树核，以调查年生长情况，并将进一步调查？同位素签名吗?记录在每个年轮内的树木使用的水源水。通过监测气候变化和从不同来源收集水，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，该研究将采用一个数值模型来评估在区域气候变化的合理情景下气候如何控制森林的取水。该项目将为森林/水/流域管理的实践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，并为本科生开设新的生态水文课程。该研究项目包括：1)对气候和水文进行实地测量，并对所有潜在树木水源的氧同位素进行实验室分析；(2)对树木年轮中的氧和碳同位素进行当代和回顾性分析，以调查最近气候驱动的树木水分利用和水分利用效率波动；(3)利用高分辨率显微切片技术对氧同位素进行季节（年内）分析。利用树木年轮来评估树木水源利用的季节波动；4)气候驱动的生态水文数值模型的改进与应用，该模型包括冲积平原动态水通量、同位素分馏/混合和树木水分吸收。它将比较沿强气候梯度的森林地点的生态水文对气候的反应。目前，将树木/森林响应与年代际气候变化联系起来的能力有限。目前还缺乏将区域气候与水的可用性以及林分上河岸树木的用水联系起来的一般性认识，这限制了森林对干旱胁迫在十年时间尺度上的响应预测能力。这项研究将使：i)确定河岸森林内水资源压力的特征；森林对气候变化响应的预测能力；Iii)在洪泛区可用水量范围内气候表达的区域变化的更清晰图景；iv)通过更好地约束不同气候强迫条件下的水分有效性和利用，改善树木-古气候重建。该研究项目将为管理人员预测和减轻气候变化对温带和地中海气候地区主要河流沿岸脆弱森林资源的风险提供新的视角和工具。该项目将举办为期两天的研讨会，向研究区域的从业者和利益相关者传播我们的研究结果。它还包括本科生研究经验（REU）补充，使两名女性和/或少数民族学生前往法国，作为他们的第一次国际旅行，参加第一次实地活动。REU将为这些学生提供令人兴奋的国际研究经验，世界一流的学习机会，并介绍环境/水文科学的潜在职业生涯。此外，该研究的数据和模型将被整合到UCSB旱地生态水文学的新高年级课程中。

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.