Bark Beetle Demography in a Jeffrey Pine Stand as Influenced by Mechanized Thinning and Prescribed Fire

摘要

Forest thinnings implemented with cut-to-length and whole-tree harvesting systems followed by underburning were evaluated for their effects on bark beetle prevalence in pure, uneven-aged Jeffrey pine fPinus jeffreyi Grev. & Balf.) interspersed with isolated California white fir fAbies concolor var. lowiana [GordJ Lemm.), Based on pitch tube counts in a stand with a moderate bark beetle population in its pine component, the Jeffrey pine beetle fDendroctonus jeffreyi Hopkins) generally preferred largertrees before treatment implementation, but after exhibiting mixed pretreatment tendencies concerning stand density demonstrated a posttreatment proclivity toward higher density. Cut-to-length thinning followed by underburning increased the pine beetle population ivhile whole-tree thinning unaccompanied by burning reduced it. Tree mortality was induced by the bark beetle infestation but was not its sole cause. Pitch tube abundance on white fir far exceeded that on Jeffrey pine, and the greatest influence on the fir engraver fScolytus ventralis LeConte) population was the prevalence of its host tree. The responses presented herein to these thinning and burning practices, which are being increasingly utilized in forest restoration efforts in the westernUSA, provide natural resource managers insight into potential forest health outcomes when implemented in Jeffrey pine and similar dry site forest types.