Susceptibility of lodgepole pine to infestation by mountain pine beetles following partial cutting of stands

Abstract

Thinning stands of lodgepole pine (Pinuscontorta Douglas var. latifolia Engelmann) is thought to increase vigor and thereby reduce susceptibility to mountain pine beetle (Dendroctonusponderosae Hopkins). Partial cut stands of lodgepole in the Kootenai and Lolo National forests, Montana, U.S.A., provided opportunity (i) to determine growth response of 76- to 102-year-old lodgepole pines following thinning and (ii) to test the hypothesis that vigor of residual trees infested and uninfested by beetles does not differ. Lodgepole pine stands receiving different partial cutting prescriptions were sampled. Characteristics measured for trees within the sample were diameter at breast height, grams of stem wood per square metre of foliage, periodic growth ratio, and leaf area. Trees in most treatments showed decreased growth the 1st year following thinning. The 1st year was followed by increased growth during the next 4 years. Of the tree characteristics measured, only dbh was significantly different on both forests between live trees and trees killed by the mountain pine beetle; the latter were larger (P < 0.001). The low amount of mountain pine beetle infestation in all stands in the presence of poor growth response and vigor of residual trees suggests that factors other than tree vigor will regulate mountain pine beetle infestations in recently thinned lodgepole pine stands. We hypothesize change in stand microclimate is the principal factor.