Effects of whitebark pine (Pinus albicaulis) restoration treatments on the distribution of bark beetle attacks

Whitebark pine is an important component of high elevation ecosystems in the western United States and Canada. Many wildlife species, including grizzly and black bears, squirrels, and birds, forage on the large, wingless seed. Whitebark pine relies heavily upon the Clark's nutcracker for seed dispersal and regeneration. Due to fire exclusion, white pine blister rust, and the mountain pine beetle, whitebark pine is declining across most of its range. In western Montana and eastern Idaho, researchers are implementing restoration treatments in an effort to combat the decline and increase natural regeneration. Treatments include silvicultural strategies, prescribed fire, and combinations of the two; the treatment that best restores and preserves whitebark pine may be implemented at a large scale in the future. This study was conducted to evaluate the effects of the restoration treatments on bark beetle attacks, to monitor flight periods of the mountain pine beetle and the pine engraver, and to survey insects infesting whitebark pine. The main study site was located on Beaver Ridge, Powell Area, Lochsa District, Cleanwater National Forest. Silvicultural treatments were implemented in summer 1998 and 1999 at this site. Tenthacre permanent plots were established throughout the treatment areas to measure tree data. Within plots, tree and site characteristics were measured and a bark beetle survey was conducted. Although bark beetle population levels were endemic, a significant treatment effect on bark beetle attacks was found using logistic regression. Bark beetles preferentially attacked trees in nutcracker opening and slashing treatments rather than control treatments. However, plots surveyed for two years, 1998 and 1999, showed no increase in bark beetle populations. The mountain pine beetle attacked only whitebark pine at the site, which supports a mixed species forest with a significant lodgepole pine component. Whitebark pine had a smaller mean diameter and height, as well as significantly more bark beetle attacks per tree than lodgepole pine. The reasons underlying mountain pine beetle preference for whitebark pine warrants further examination. The results of this study show that managers must consider the insect component of whitebark pine ecosystems before implementing restoration treatments.