The enigma of yellow-cedar decline: what is killing these long-lived, defensive trees?

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Yellow-cedar, also known as Alaska-cedar (Chamaecyparis nootkatensis), is ecologically important and economically valuable in coastal Alaska and British Columbia. It is a beautiful and fascinating tree whose common name is derived from its bright yellow heartwood. Native Alaskans used the tree's wood and bark extensively, and the Russians built ships from its strong and durable wood when they occupied Alaska in the 1800s. The wood is currently exported to Asian markets; it is especially sought in Japan. Yellow-cedar's ecological strategy seems to be one of defense: tolerate harsh sites where competition is at a minimum, put relatively few resources into growth and reproduction, and outlive competitors. The color and distinct aroma of its heartwood come from powerful natural biocides, such as nootkatin. The foliage contains volatile leaf oils that probably restrict insect feeding. Yellow-cedar has few serious insect and disease pests and can live a millennium or longer. Despite those defenses, something has been killing yellow-cedar since the 1880s across numerous islands on more than 500,000 acres of forest in southeast Alaska, generating the most severe forest decline in western North America. Large concentrations of snags accumulate as the wood's natural durability allows dead trees to persist standing for decades. Yellow-cedar decline appears to be an outstanding example of a naturally induced forest decline. Extensive mortality before 1900 on numerous remote, undisturbed sites without nearby sources of anthropogenic pollutants argues against atmospheric pollution as the cause of decline. Climatic warming, which apparently coincided with the onset of extensive yellow-cedar mortality, could be responsible for triggering some stress factor that has led to the demise of yellow-cedar forests on some 500,000 acres. Warmer temperatures could influence crucial environmental factors by, for example, changing winter precipitation from snow to rain. Changes in temperature or precipitation may affect decomposition processes, perhaps resulting in the formation of soil compounds toxic to yellow-cedar. Research on possible abiotic factors, such as 10 December 1997 freezing of fine roots and soil toxicity, and their link to climatic change, could solve the mystery. If climate has been a trigger, then yellow-cedar decline in Alaska may be an excellent example of the devastating effects of a moderate climate shift on a forest ecosystem. Long-lived tree species that do not reproduce often, such as yellow-cedar, may be unable to adapt to a changing environment. That inability to adapt could explain the enigma of what is killing this defensive tree.

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Reference Code: U97HEN01IDUS

Full Citation: Hennon, P. E. and C. G. Shaw III. 1997. The enigma of yellow-cedar decline: what is killing these long-lived, defensive trees? Journal of Forestry 95(12): 4-10.

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