Climate Change, Forest Management, Stream Temperature and Salmonids

There has been concern for decades about the individual effects of climate change and forest harvesting on stream temperature, to a large extent motivated by concerns regarding the effects on salmonid habitat suitability. This presentation explores the effects of climatic variability and forest harvesting, both individually and in combination, on stream thermal regime and its consequences for resident cutthroat trout. Stream temperature data have been recorded for a set of headwater streams in the southern Coast Mountains of British Columbia, including both unlogged controls and catchments subject to clearcut harvesting with and without riparian buffers. Time-series regression models are used to relate pre- and post-harvest stream temperatures in treatment streams to the corresponding temperatures recorded in the control streams. These regression models are used to generate multi-year time series of with-harvest and without-harvest stream temperatures for the treatment streams. Regression models are also used to explore the sensitivity of stream temperature to weather conditions. Forest harvesting has its greatest effect on stream temperature in spring, summer and early autumn. The effects of forest harvesting interact with prevailing weather conditions, with the greatest effects occurring during periods of warm, dry weather. Given that summers in the Pacific Northwest are projected to become warmer and drier, summer stream temperature is likely to become more sensitive to forest management. While winter stream temperature is relatively insensitive to the effects of harvesting, it does vary substantially according to prevailing weather conditions and thus will be sensitive to climatic change. The potential effects of future climatic scenarios and forest management on resident trout populations are explored using a bioenergetics model.