RII Track-4: NSF: Does warming-driven root damage lead to drought stress in declining yellow-cedar trees?

在北美西北部的温带雨林中，黄杉（Callitropsis nootkatensis）正在经历广泛的枯死。重要的证据支持这样一种观点，即全球变暖导致的绝缘积雪的减少，使黄杉（YC）的根受到霜冻损害，最终导致树木死亡。该项目的目的是为了更好地了解气候变化是如何影响黄杉（YC）的，黄杉是一种广泛减少的标志性树种。迄今为止，超过3000平方公里的YC森林经历了严重的枯死，这对阿拉斯加东南部和不列颠哥伦比亚省的经济、生态和文化产生了深远的影响。黄杉现在被认为是全球森林健康状况因人为变暖而下降趋势的“典型代表”，而成功的保护黄杉的努力将取决于确定气候变化和树木死亡之间的所有联系。在异常的冬末天气期间，霜冻对YC根系造成的干旱胁迫是枯死过程中一个未经检验但可能至关重要的环节。通过阿拉斯加费尔班克斯大学（UAF）和亚利桑那大学的合作，该项目将通过应用新开发的方法分析雪松木材解剖结构，测试YC树木是否表现出干旱压力的症状。除了同行评议的出版物和由一名早期职业研究人员领导的会议报告外，该项目还包括一个为期一周的研讨会，由阿拉斯加Kake土著社区的K-12学生和森林管理者参加。该项目的主要目标是检验“冻害根”假说的一个重要推论；即，YC根系损伤导致干旱胁迫和最终的树木死亡。为了避免空化，干旱胁迫下的针叶树在年轮内放置了直径更细、壁更厚的管胞细胞，这些解剖变化可以用定量木材解剖（QWA）的新方法来记录。本项目将使用这些方法来验证预测，即相对于附近健康的YC树生长的相同年轮，衰落和死亡的YC树的外年轮管胞的管腔面积明显更小，壁更厚。为了实现这一目标，UAF的研究者将与亚利桑那大学树木年轮研究实验室的一位合作者合作，将QWA方法应用于从阿拉斯加东南部收集的长期死亡，积极衰退和目前健康的YC树木。这些结果将为气候变化和森林枯死提供新的见解，并使利益相关者能够更准确地预测霜冻损害和干旱对这一重要树种的影响。此外，该项目将通过获得新的分析方法来扩大UAF的研究基础设施，这将有利于阿拉斯加的一系列环境研究。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Yellow-cedar (Callitropsis nootkatensis) is now experiencing widespread dieback in the temperate rainforests of northwestern North America. Significant evidence supports the idea that a loss of insulating snow cover caused by global warming exposes yellow-cedar (YC) roots to frost damage, which eventually leads to tree death. The purpose of this project is to better understand how climate change is affecting yellow-cedar (YC), an iconic tree species in widespread decline. To date, over 3,000 km2 of YC forests have experienced significant dieback, which has had far-reaching economic, ecological, and cultural effects in Southeast Alaska and British Columbia. Yellow-cedar is now considered a “poster child” of the global trend of declining forest health in response to anthropogenic warming, and successful YC conservation efforts will hinge on identifying all the links between climate change and tree death. Drought stress in the aftermath of frost damage to YC roots during periods of anomalous, late-winter weather is an untested yet potentially critical link in the dieback process. Through a collaboration between the University of Alaska Fairbanks (UAF) and the University of Arizona, this project will test whether declining YC trees exhibit symptoms of drought stress by applying newly developed methods to analyze cedar wood anatomy. In addition to peer-reviewed publications and conference presentations led by an early-career researcher, this project will involve a week-long workshop with K-12 students and forest managers in the Alaska Native community of Kake. The primary goal of this project is to test an important corollary of the “frost-damaged root” hypothesis; namely, that YC root injury results in drought stress and eventual tree mortality. To avoid cavitation, drought-stressed conifer trees lay down thinner-diameter and thicker-walled tracheid cells within their annual rings, and these anatomical changes can be documented using new methods in quantitative wood anatomy (QWA). This project will use these methods to test the prediction that tracheid cells in the outer rings of declining and dead YC trees have significantly lower lumen areas and thicker walls relative to the same annual rings grown in nearby healthy YC trees. To accomplish this, the investigator from UAF will work with a collaborator at the Laboratory of Tree-Ring Research at the University of Arizona to apply QWA methods on long dead, actively declining, and currently healthy YC trees collected from Southeast Alaska. These results will provide new insight about climate change and forest dieback and will allow stakeholders to predict the impacts of frost damage and drought more accurately on this important tree species. In addition, this project will expand research infrastructure at UAF by acquiring new analytical methods that will benefit an array of environmental research in Alaska.This 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.