Relationship of Growth Reduction in Douglas-fir to Infection by Armillaria Root Disease in Southeastern British Columbia

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Abstract
Stem volume growth during consecutive 5-yr periods was measured in four Douglas-fir (Pseudotsuga menziesii) stands infected by Armillaria ostoyae in the interior cedar-hemlock and montane spruce biogeoclimatic zones of southeastern British Columbia. Growth, expressed as percent of stem volume at the start of each period, decreased significantly as resinosis increased due to mycelial colonization of tree base. It was highest in resinosis severity class 0 (healthy), lowest in classes 3 (> 50-100% of basal circumference showing resinosis) and 4 (recently killed, 100% resinosis), and intermediate in classes 1 (no basal resinosis but root[s]infected within 1 m of root collar) and 2 (.ltoreq. 50% basal resinosis). Differences among classes were greatest for the past 5-yr period and least, though still significant, for the past 15-yr period. Trends during the past 30 yr showed greater declines in severity classes 3 and 4 relative to class 0 than in classes 1 and 2. The period in which decline was initiated also occurred earlier (up to 25 yr ago) in classes 3 and 4 than in other classes. The percentage of basal circumference that was affected by lesion was strongly related to percent roots infected by only weakly to percent volume growth. The relation of percent basal circumference affected by lesion to percent volume growth was greatly strenthened by including the period in which decline was initiated in the regression equation.

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