Decline of Western Red Cedar: Using Tree Rings to Understand Mortality Patterns and Identify Drought-Resilient Populations Under Climate Change

  • U.S. Forest Service
  • WA Dept of Natural Resources
  • OR Dept of Forestry
  • Idaho Dept of Lands
  • B.C. Forests, Lands, Natural Resource Operations and Rural Development
In Progress

Western red cedar (Thuja plicata) is a long-lived conifer that is culturally and economically centered in the Pacific Northwest. Over the past several decades, forest health specialists, private landowners and managers have observed a progressive decline in western red cedar. Stands in decline across the species’ range have been reported to exhibit thinning crowns, heavy cone crops, foliage discoloration and widespread mortality. Although western red cedar dieback is known to be widespread, the geographic extent of its mortality has been difficult to capture through typical aerial detection surveys, where its slow dieback can be masked by more dominant crowns of Douglas-fir or western hemlock.

Drought during the growing season and reduced April snowpack are suspected causes of western red cedar decline, which are likely to become more prevalent challenges with future climate change. However, the geographic extent and underlying causes of both western red cedar dieback and resilience are unclear. Comprehensive, quantitative examinations of western red cedar resiliency to co-occurring climate stresses are needed in order to effectively manage and protect western red cedar in a changing climate.

To help address this research need, this study combines field-based data collection, tree ring measurements, statistical analyses and computer-modeling to provide insights about site characteristics that sustain or degrade western red cedar growth and resilience to drought. The tree ring measurements will provide detailed information about how this species has been reacting to changes in climate, while the remote sensing and modeling will help inform forest management actions critical to the longevity of this iconic and culturally important species.