Ponderosa pine mortality during a severe bark beetle (Coleoptera: Curculionidae, Scolytinae) outbreak in southern British Columbia and implications for wildlife habitat management

摘要

We examined the extent and severity of bark beetle (Dendroctonus sp.) attack in ponderosa pine forests in southern British Columbia using stand monitoring plots and forest insect overview survey data, and relate these results to vertebrate wildlife habitat conditions. Monitoring plots established in ponderosa pine stands in 2007 indicate overall mortality levels of 77.8% for trees >7.5cm dbh by 2008, with lower mortality rates for small stems in the 7.6-15cm dbh range (53%) and very high mortality (94.9%) of large stems >30cm dbh. Data from insect overview surveys indicated the attack was extensive and continues to expand. In the Kamloops district, 52,126ha, or 36% of the area with ponderosa pine as a component of the stand was attacked in 2007 alone, with many areas likely attacked in more than one year. The current bark beetle attack represents a strong thinning from above disturbance that is extensive and will have long-term consequences for canopy closure and overstory structure. These changes will have implications for species dependant on mature overstory trees or large snags for foraging and nesting, with effects greatest in pure stands of ponderosa pine. In mixed stands of ponderosa pine and Douglas-fir, ponderosa pine mortality will likely enhance habitat for species dependent on mature or old forest structure by increasing levels of snags, downed wood and creating natural within-stand gaps and heterogeneity. An extensive natural disturbance like the current bark beetle outbreak, following the extensive harvesting in ponderosa pine forests between 1850 and 1950 may frustrate management attempts to provide future diverse habitat conditions for flora and fauna, and other commodities such as viewscapes, recreation and timber. Silvicultural interventions can facilitate the development of mature conditions in some pure stands of ponderosa pine where mature trees have been killed, and should be considered to reconcile current conditions with desired mid- and long-term habitat requirements