Distribution of Attacks by Dendroctonus ponderosae Hopk. on Pinus contorta Dougl. var. latifolia Engelm.

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Abstract
The incidence of attacks by Dendroctonus ponderosae Hopk. (= monticolae) was recorded by square-foot quadrats from the total bark surface of 60 lodgepole pine trees, Pinus contorta Dougl. var. latifolia Engelm., according to location on the tree, proximity to branches, and degree of bark roughness. The frequency distribution of attack density was bimodal, but the bimodality was an artifact of sampling from a population having a varying mean density. A log (x + 1) transformation of the data permits the use of parametric tests. Alternative non-area sampling techniques showed that the spatial distribution of attacks within a small area tended toward regularity, probably following the distribution of bark niches. The greatest variance in attack density was associated with height, followed by areas, trees, diameters and aspects. Bark roughness was an important influence of distribution but number of branches was not.