Mountain Pine Beetle-Caused Tree Mortality in Partially Cut Plots Surrounded by Unmanaged Stands

Mountain pine beetle activity was monitored in one set of 2.5 acre plots in the southern portion of the Black Hills National Forest over a 17-year period. Beetles attacked 77 percent of the trees in the uncut control, 48 percent of the trees in the growing stock level (GSL) 100/110, 53 percent of the trees in the GSL 80/90, and 9 percent of the trees in the GSL 60/70. The percentages of MPB-attacked trees in each 1 in diameter class were lowest in the GSL 60/70, intermediate in the GSL 80/90 and GSL 100/110, and highest in the uncut control. Live basal area was significantly reduced in the GSL 80/90, GSL 100/110, and control but not in the GSL 60/70. Partial cutting to reduce beetle-caused mortality may be ineffective for partially cut parcels of <10 acres if the partially cut stands are surrounded by unmanaged susceptible stands. To increase the effectiveness of partial cutting, stands should be managed on a landscape basis. A 100-ft-wide strip with stand density of ≤GSL 70 between unmanaged and managed stands may be sufficient to limit the spread of beetle-caused mortality from unmanaged stands to adjacent partially cut stands.