Canadian Forest Service Publications
Effects of climate and weather on mountain pine beetle populations. 1978. Safranyik, L. Pages 77-84 in A.A. Berryman, G.D. Amman, and R.W. Stark, Editors. Proceedings of Symposium on Theory and Practice of Mountain Pine Beetle Management in Lodgepole Pine Forests, April 25-27, 1978, Washington State University, Pullman, Washington. College of Forestry, Wildlife and Range Sciences, University of Idaho, Moscow, Idaho.
Issued by: Pacific Forestry Centre
Catalog ID: 1819
The literature on the direct effects of climate and weather on the biology and dynamics of mountain pine beetle (Dendroctonus ponderosae Hopkins) populations is reviewed and discussed, with emphasis on the development of epidemics. Of the climatic effects, temperature is the most important. Typically, in the optimum range of the beetle's distribution on lodgepole pine (Pinus contorta Douglas var. latifolia Engelmann), there is enough heat accumulation each year to produce one or more generations and the frequency of adverse weather conditions is not high enough to prevent population build-up or to reduce infestations to endemic levels. In some years, however, adverse weather can cause a decline in population and damage levels, but this reversal is usually temporary and the course of outbreak is largely determined by factors other than climate. In this optimum habitat, the beetle poses a continuous threat to lodgepole pine of susceptible age and size. At high elevation and at northern latitudes, climate becomes the dominant factor controlling the distribution and abundance of mountain pine beetle populations and infestations in space and time. Beetle development is out of phase with the cold season; consequently, the least cold-hardy life stages (eggs, pupae) may enter the winter and suffer heavy mortality. Epidemics tend to be less frequent and intense, and stand depletion decreases, toward the limits of the distributional range. The northern limit of the beetle's range is bounded by the isotherm for -40°C (-40°F) mean annual minimum temperature and a zone where, on the average, heat accumulation during the growing season is less than the estimated minimum (833 degree-days C) for brood development on a 1-year cycle. The upper altitudinal limit, which ranges from about 750 m (2460 ft) near the northern limit (latitude 56°N) to about 3650 m (11,972 ft) near the southern limit (latitude 31°N), is probably delimited by similar temperature conditions.