Ponderosa pine stands were partially cut to various stocking levels at five locations, periodically surveyed, and remeasured during the 20 years after installation. Mean diameter generally increased 2 inches over the 20-year period on most partially cut plots and less than 2 inches on unmanaged controls. Average diameter growth for diameter classes in partially cut plots was generally significantly greater than average diameter growth for the same diameter classes in uncut control plots. Basal area increased 20 to 40 ft 2 /acre in partially cut plots and 5 to 21 ft 2 /acre in unmanaged controls at four locations over a 20-year period. Beetle-caused mortality ranged from 0 to 51 percent of the trees in partially cut plots and from 1 to 77 percent of the trees in control plots although mortality was generally <8 percent in partially cut plots. Beetles attacked trees ranging from 8 to 18 inches in partially cut stands and from 7 to 19 inches in unmanaged stands. Beetles did not exclusively attack >16-inch diameter trees, so some trees >16 inches may be selected as leave trees. However, if an infestation persisted in a stand, trees in diameter classes >16 had the highest percentage mortality. The effectiveness of partial cutting for minimizing mountain pine beetle-caused mortality is influenced by: residual stocking level, size of the partial cut, amount of time since the area was cut, and proximity of beetle populations. Partial cuts of <10 acres may not minimize beetle-caused mortality if the cut stands are surrounded by unmanaged forest. Management to minimize beetle-caused mortality should be considered the top priority in mature ponderosa pine stands.

Ten-year diameter and basal area growth were determined for partially cut stands at 4 locations. Average diameters in the partially cut plots generally increased by 1 inch or more, while average diameter in the uncut controls increased by 0.9 inches or less. Individual tree growth is discussed in relation to potential susceptibility to mountain pine beetle infestation. Basal area increases ranged from 0.9 to 1.9 ft2/acre/ yr in partially cut plots, while basal area increases in the control plots ranged from 0.4 to 1.4 ft2/acre/yr. Endemic mountain pine beetle infestations and snow breakage accounted for most of the mortality on the plots, which decreased the residual basal area and basal area growth. Increases in basal area are used to estimate the length of time required for various stand densities to reach the susceptibility thresholds for mountain pine beetle infestation. Stand marking may influence future susceptibility to beetle infestations.