Mountain Pine Beetle Caused Tree Mortality In Partially Cut Plots Surrounded By Unmanaged Stands

Periodic diameter and basal area growth were determined for partially cut stands of lodgepole pine at five locations over approximately 10 year periods. After cutting, average diameters in the partially cut plots generally increased by 0.8 inches or more, while average diameter in the uncut controls increased by 0.6 inches or less. Diameter growth in the partially cut plots was generally significantly greater than diameter growth in the controls. Individual tree growth is discussed in relation to potential susceptibility to mountain pine beetle infestation. Basal area decreased in three of the four GSL (growing stock level) 40 stands because of windthrow. Basal area generally increased >1.0 ft 2 / acre/year in partially cut plots except in the GSL 40 stands with substantial windthrow and one GSL 100 with an Armillaria infection pocket. Basal area increases in the control plots ranged from 0.2 to 1.1 ft 2 /acre/year, although the one control with a BA growth rate of 1.1 ft 2 /acre/year had a relatively low initial BA. Data from the stands are employed in the susceptibility rating methods of Amman et al.(1977), Shore and Safranyik (1992),and Anhold et al. (1996 to determine stand susceptibility and the results discussed in terms of general applicability of these methods to partially cut stands. Basal area growth is used to estimate the length of time required for various stand densities to reach specific susceptibility thresholds for mountain pine beetle infestation. Several of the GSL 40 stands are not projected to reach the susceptibility thresholds in 100 years because of windthrow. Barring mortality 1%,GSL 80 stands are estimated to reach the basal area threshold of 120 ft 2 per acre in

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.