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Decline and Mortality of Chamaecyparis nootkatensis in Southeastern Alaska, a Problem of Long Duration but Unknown Cause. Charles G. Shaw III, Principal Research Plant Pathologist, USDA Forest Service, Pacific Northwest Forest and Range Experiment Station, Forestry Sciences Laboratory, Juneau, AK 99802. Andris Eglitis, Entomologist, and Thomas H. Laurent, Pathologist, USDA Forest Service, Alaska Region, State and Private Forestry, Juneau 99802; and Paul E. Hennon, Graduate Research Assistant, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331. Plant Dis. 69:13-17. Accepted for publication 25 June 1984. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1985. DOI: 10.1094/PD-69-13.

Alaska-cedar (Chamaecyparis nootkatensis) trees have been dying of an unknown cause in large numbers at several locations in southeastern Alaska for more than 75 yr. At least 9,700 ha of cedar forest have been affected. Diseased stands often have 50% or more of their total volume in Alaska-cedar, of which 25% or more is dead or dying. Decline and mortality of small understory cedar trees have occurred either along with or after decline and mortality of larger overstory trees. Affected trees either die quickly and turn brown after a few growing seasons or decline and die slowly with their crowns gradually changing color and decreasing in fullness for 5 yr or more. Diameter growth decreases with crown deterioration. Some trees respond to foliage loss by producing bushy, epicormic branches. The cedar bark beetle (Phloeosinus cupressi), previously suggested as a cause of mortality, was found to be a secondary agent that only attacked trees in advanced decline. Armillaria sp. occurred frequently on dead and dying trees but not consistently on recently killed trees, suggesting that it is not the primary cause. No other known pathogens were isolated from affected trees. The patterns of tree death and decline are consistent with a hypothesis that environmental stress is the primary cause of the problem.