The impact of projected climate change on spruce and Douglas fir forests in British Columbia was assessed using bioclimatic envelope models. Present and future climatic suitability was modelled for Douglas fir, Engelmann spruce, hybrid spruce, and white spruce. A correlative modelling technique based on principal component analysis was employed to determine climatic suitability throughout British Columbia. The models were developed using elevation-adjusted interpolated records of the 1961-1990 climate baseline. Future suitability was modelled using climate data from six projections derived from five different Global Climate Models (GCMs) under three emissions scenarios. All projections indicate a shift in suitability for both spruce and Douglas fir to higher elevations and latitudes than their current range. However, significant differences exist between the projections with regard to the pace, extent and fine-scale details of these changes. This uncertainty was investigated by comparing individual projections to each other and presenting results of agreement between models. The effect of spatial resolution was also investigated. The impact of pest suitability was assessed with a simple climate envelope method based on empirically derived climate thresholds affecting locations of historical pest outbreak occurrence of western spruce budworm (WSBW) and spruce bark beetle (SBB). Future projections show increased outbreak risk in central and northwestern British Columbia for two climate scenarios and both pest species. By the end of the century, considerable portions of the Province have no analogue to past outbreak conditions.

The tree suitability and pest suitability results were processed together with forest inventory data by an economic model that considers major stand-level harvest decisions such as greenup constraints, preserves large tracts of old-growth forest, and an even flow of harvest. The model was solved using an iterative spatial optimization method that has good convergence properties. The model was applied to data for the Okanagan TSA and for the entire Province of BC. The results (based on climate influence on tree species and pest outbreaks for Douglas fir/WSBW and spruce/SBB only) show that the economic impact of climate change is a modest improvement or no change, depending on climate scenario, for the Province overall, but that there is a negative economic impact for the Okanagan TSA in all cases.