COLONIZATION PATTERNS OF THE MOUNTAIN PINE-BEETLE IN THINNED AND UNTHINNED LODGEPOLE PINE STANDS

Outbreak populations of the mountain pine beetle, Dendroctonus pondero sae Hopkins, in central Oregon, were analyzed with an autologistic reg ression model to evaluate colonization patterns in thinned and unthinn ed plots of lodgepole pine, Pinus contorta Dougl. Results confirmed pr evious observations that beetle attacks in unmanaged stands were relat ed to tree diameter and spacing among trees. Beetles showed a decided preference for colonizing trees with large diameters. Trees with small diameters were rarely attacked unless they were close to other trees under attack. Thinned plots were initially unattractive to beetles, bu t when attacks occurred, colonization was not very different from the pattern in unthinned plots. Conditional probabilities of attack for tr ees near other attacked trees were actually greater in thinned plots, indicating that the wide spacing between trees in these plots did not seem to interfere with the switching of attacks between trees. Vigor w as not a significant covariate for estimating probability of attack in the unthinned plots. It was significant for one of the thinned plots, however, and marginally significant for another. Only one tree was co lonized in a third thinned plot that had the widest spacing and the gr eatest vigor. A surprise was that some of the oldest trees on thinned plots appeared resistant to attack; their resistance was unrelated to diameter, vigor, or position relative to other attacked trees.