Analysis of Spatial Patterns of Lodgepole Pine Attacked by Outbreak Populations of the Mountain Pine Beetle
Five years of mountain pine beetle, Dendroctonus ponderosae Hopkins, attacks on lodge-pole pine, Pinus contorta Dougl., were analyzed in an early outbreak situation using generalized linear models to shed light on patterns in the colonization process. The chosen logit model indicated three covariates as significant factors in the probability of trees being colonized by the mountain pine beetle. The first covariate related to tree size and spatial relationships among trees colonized the same year; its effect was most obvious for trees in the smaller diameter classes. The other two covariates correlated with tree diameters and vigor, and they indicated a greater probability of attack for larger trees and trees with low vigor. The model showed that the probability of trees being colonized in this stand increased significantly as the outbreak gained momentum, but only as long as the food supply (trees with dbh ≥ 23 cm) was abundant. It also showed that the pattern of selection of large and small trees did not change significantly as beetle pressure increased over time. Findings suggested that big trees were important to outbreaks beyond simply generating beetles, and that many trees were colonized only because they were dose to other trees under attack. For. Sci. 37(5):1390-1408.
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