Bark beetle and wood borer infestation in the greater Yellowstone area during four postfire years

Abstract

Extensive surveys of bark beetles and wood bores in the Greater Yellowstone area were conducted in 1991 through 1993. The study objectives were to determine the effect of delayed tree mortality following the 1988 fires on mosaics of fire-killed and green tree stands, the relationship between fire injury and subsequent infestation, and the effect of insect buildup in fire injured trees on infestation rates for uninjured trees. Surveys were conducted adjacent to roads, and plots wee selected randomly. In 1991, 321 plots were measured, 198 plots in 1992, and 127 plots in 1993. Insects killed 12.6 percent of the Douglas-fir, 17.9 percent of the lodgepole pine, 6.6 percent of the Engelmann spruce, 7.5 percent of the subalpine fire, and 2.8 percent of the whitebark pine. Delayed mortality attributed to fire injury accounted for more mortality than insects. Both types of mortality greatly altered the original fire-killed/green tree mosaics that were apparent immediately after the 1988 fires. Insect infestation was strongly and positively correlated with the percent of the basal circumference of the tree that was fire killed in the species, except in Engelmann spruce where infestation peaked in the middle fire-injury class. Infestation in Douglas-fir, lodgepole pine, and Engelmann spruce increased through 1992 then declined in 1993. Although it cannot be said with certainty that insects built up in fire-injured trees and then caused increased infestation of uninjured trees, the high level of infestation suggests this is the case.