Canadian Forest Service Publications
Forest, climate and mountain pine beetle outbreak dynamics in western Canada. 2006. Taylor, S.W.; Carroll, A.L.; Alfaro, R.I.; Safranyik, L. Pages 67-94 (Chapter 2) in L. Safranyik and W.R. Wilson, editors. The mountain pine beetle: a synthesis of biology, management, and impacts on lodgepole pine. Natural Resources Canada, Canadian Forest Service, Pacific Forestry Centre, Victoria, British Columbia. 304 p.
Year: 2006
Issued by: Pacific Forestry Centre
Catalog ID: 26040
Language: English
Availability: PDF (download)
Abstract
Mountain pine beetle (Dendroctonus ponderosae Hopk. [Coleoptera: Scolytidae]) outbreaks have been observed in all pine species in western Canada. However, they have occurred principally in lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia) in the southern half of British Columbia and the extreme south-western portion of Alberta, with one outbreak recorded in the Cypress Hills at the southern junction of the Alberta–Saskatchewan border. At least four large-scale outbreaks have occurred in western Canada in the past 120 years, as documented in forest survey records or detected as growth releases in tree rings. The Chilcotin Plateau in central interior British Columbia has sustained the most years of outbreak. Dendrochronological evidence suggests an outbreak periodicity of about 40 years in this region.
The size of mountain pine beetle infestations varies with short-term changes in weather and long-term changes in host availability. Retrospective modelling suggests that both the amount of susceptible mature lodgepole pine and the area with favourable climate have increased during the past century. An age-class projection model using contemporary forest inventory data in combination with wildfire and harvesting statistics suggests that during the early 1900s, approximately 17% of pine stands were in age-classes susceptible to mountain pine beetle attack. Forest age-class structure is controlled by the disturbance regime. In unmanaged lodgepole pine forests, wildfire was the primary disturbance agent. With fire-return cycles of 40 - 200 years, the long-term average susceptibility to mountain pine beetle would be about 17% - 25% over large areas. However, during the past 80 years the amount of area burned by wildfire in pine forests in British Columbia has significantly decreased. While harvesting has also increased during this same period, the net disturbance rate is believed to have decreased. The reduction in disturbance rate has resulted in an increase in the average age of pine stands such that approximately 55% of pine forests are presently in age-classes considered susceptible to mountain pine beetle. Analysis and modelling of the historical distribution of a climatic suitability index and of outbreaks suggests that over the past 40 years the range of mountain pine beetle has expanded, as has the area that is climatically favourable for it. Thus, an increase in both the amount of susceptible-aged host and range expansion due to a more favourable climate have created ideal conditions for the development of an extensive mountain pine beetle epidemic. A better understanding of the effect of forest dynamics and climatic variation on mountain pine beetle populations and outbreak development will allow for management of lodgepole pine with regard to disturbance risk.