Growth response in a Douglas-fir/lodgepole pine stand after thinning of lodgepole pine by the mountain pine beetle: A case study

Abstract

Diameter growth response was measured in a mixed stand of lodgepole pine, Pinus contorta Dougl. ex Loud, and interior Douglas-fir, Pseudotsuga menziesii var glauca (Beissn.) Franco, in the Cariboo Forest Region of British Columbia, 14 years after an outbreak of the mountain pine beetle, Dendroctonus ponderosae Hopkins, killed 76% of the pine. Nearly all Douglas-fir and a large proportion of the lodgepole pine responded to the beetle-induced thinning with a diameter growth increase which persisted 14 years after the infestation. Douglas-fir trees gained an average 1.4 em or 11.7% in diameter over the estimated size the trees would have reached in the absence of the thinning effect. Annual growth rates of Douglas-fir in the post-outbreak period averaged 2% per year without the beetle-induced thinning and 2.9% after thinning. The surviving lodgepole pine trees gained an average 1 em or 5.4% in diameter over the size the trees would have reached in the absence of the thinning effect. In the post-outbreak period, annual diameter growth rates of the pine doubled from 0.4% per year without the thinning , to 0.8% per year with thinning. The thinning response in Douglas-fir was inversely related to the initial diameter and age of the trees at the start of the infestation but that of pine was not.