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Influence of Dwarf Mistletoe and Western Spruce Budworm on Growth and Mortality of Douglas-Fir in Unmanaged Stands

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Permanent inventory plots in 94 unmanaged stands of primarily Douglas-fir (Pseudotsuga menziesii) on three national forests in Oregon and Washington were examined for growth suppression caused by dwarf mistletoe (Arceuthobium douglasii) and western spruce budworm (Choristoneura occidentalis). Ten-year increments of diameter and basal area were calculated from measurements in 1977-1987. Severity of dwarf mistletoe was scored using the six-class system. Severity and duration of defoliation were determined from aerial maps drawn over a 20-yr period. Dwarf mistletoe significantly decreased 10-yr diameter increment. Western spruce budworm significantly reduced diameter increment and basal area increment. No significant interactions between defoliation and dwarf mistletoe were found. Ten-year mortality of Douglas-fir due to dwarf mistletoe averaged 5% and 2% of the infected trees and basal area, respectively, for stands with moderate dwarf mistletoe severity and 4% and 3% of the infected trees and basal area, respectively, for stands with severe dwarf mistletoe infestation. Mortality was highest in stands with the most dwarf mistletoe and in stands with the most severe defoliation. There were no significant differences in diameters of dead trees among severity classes for dwarf mistletoe. Dead-tree diameters were significantly smaller in stands with the most severe defoliation during the measurement period. For. Sci. 39(3):465-477.

Keywords: Arceuthobium douglasii; Choristoneura occidentalis; Pseudotsuga menziesii; diameter and basal area increment; pest impact assessment

Document Type: Journal Article

Affiliations: Biological Technician, Pacific Northwest Research Station, USDA Forest Service, 1401 Gekeler Lane, La Grande, OR 97850

Publication date: August 1, 1993

More about this publication?
  • Forest Science is a peer-reviewed journal publishing fundamental and applied research that explores all aspects of natural and social sciences as they apply to the function and management of the forested ecosystems of the world. Topics include silviculture, forest management, biometrics, economics, entomology & pathology, fire & fuels management, forest ecology, genetics & tree improvement, geospatial technologies, harvesting & utilization, landscape ecology, operations research, forest policy, physiology, recreation, social sciences, soils & hydrology, and wildlife management.
    Forest Science is published bimonthly in February, April, June, August, October, and December.

    2015 Impact Factor: 1.702
    Ranking: 16 of 66 in forestry

    Also published by SAF:
    Journal of Forestry
    Other SAF Publications
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