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

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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.