Periodicity of Two-Year Cycle Spruce Budworm Outbreaks in Central British Columbia: A Dendro-Ecological Analysis
Four periods of decade-long reduced growth attributable to budworm defoliation were identified in the increment cores from both spruce and subalpine fir. These occurred in the mid-1890s to the early 1900s, the mid-1920s to the mid-1930s, the 1950s to the early 1960s, and the late 1980s to present (1999). Outbreaks recurred approximately every 32 yr. The reduced growth period, indicative of past outbreaks, consisted of a growth reduction phase lasting 7 to 11 yr in which rings generally exhibited a pattern of alternating wide and narrow rings (a “saw-tooth” pattern). This pattern was attributed to the biennial nature of the life cycle of this budworm, in which severe damage is caused every other year. The growth reduction phase was followed by a growth recovery phase lasting 3 to 5 yr in which ring-width gradually returned to pre-outbreak levels. Thus, the entire growth loss period could last from 10 to 16 yr and cause an average annual loss in radial increment from 16 to 21%. The 32 yr cycle of outbreak recurrence was attributed to changes in forest structure in which the forest evolves from a nonsusceptible to a susceptible state as the proportion of subalpine fir present in the upper canopy increases relative to the spruce component. A 2 yr cycle budworm outbreak will selectively remove the subalpine fir component returning the forest to a less susceptible state. It was concluded that the 2 yr cycle budworm is an important disturbance agent of northern British Columbia forests causing significant growth loss. FOR. SCI. 48(4):722–731.
Keywords: Insect disturbance; environmental management; forest; forest growth; forest management; forest resources; forestry; forestry research; forestry science; herbivory; natural resource management; natural resources; tree-ring
Document Type: Miscellaneous
Affiliations: 1: Professor Cold and Arid Regions Environmental and Engineering, Research Institute, Chinese Academy of Sciences, 260 Dong-Gang-Xi-Lu, Lanzhou, Gansu, 73000, P.R. China, Phone: 86-931-8278490; Fax: 86-931-8273894 [email protected] 2: Senior Research Scientist Pacific Forestry Centre, Canadian Forest Service, 506 West Burnside Road, Victoria, BC, Canada, V8Z 1M5, Phone: 250-363-0660; Fax: 250-363-0775 [email protected]
Publication date: 2002-11-01
- 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.
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