In western Canada, the operational risk rating system for mountain pine beetle is based on biological knowledge gained from a rich legacy of stand-scale field studies. Owing to the large spatial and temporal extents of the current epidemic, new research into large-area mountain pine beetle processes has revealed further insights into the landscape-scale characteristics of beetle infested forests. This research evaluates the potential for this new knowledge to augment an established system for rating the short-term risk of tree mortality in a stand due to mountain pine beetle.--Publisher's website.

The mountain pine beetle, Dendroctonus ponderosae Hopkins, is a significant agent of tree mortality in lodgepole pine (Pinus contorta Dougl. ex Loud.) forests throughout western North America. A large outbreak of mountain pine beetle caused extensive tree mortality in north-central Colorado beginning in the late 1990s. We use data from a network of plots established in 2006-2007 on the Sulphur Ranger District of the Arapaho and Roosevelt National Forests to develop simple probability of infestation and extent of mortality models using classification and regression trees, respectively. A classification tree indicated that when live lodgepole pine basal area was equal to or greater than 59.3 ft2/acre pre-outbreak, the probability of infestation increased. A second classification tree added lodgepole pine mean diameter as a second splitting variable. The rate of correct classification for both models was greater than 0.79. Two regression trees also used live pre-outbreak lodgepole pine basal area as a splitting variable and indicated increasing basal area killed with increasing live lodgepole pine basal area. These simple models use readily available data from forest inventories and can be used to identify stands, based on forest stand conditions, where mountain pine beetle is more likely to occur and the potential extent of lodgepole pine tree mortality should an outbreak occur.

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