Local and Longitudinal Stream Temperature Response to Timber Harvest in the Trask Watershed Study Area

The Trask Watershed Study is a multi-disciplinary, long-term research project in the Oregon Coast Range which examines the effects of current forest management practices on aquatic ecosystems.  One of the key physical parameters is stream temperature.  Stream temperature is a dynamic, non-linear parameter that responds to changes in local and regional conditions and is a primary factor in structuring aquatic communities in lotic ecosystems.  Quantifying stream temperature variability before and after timber harvest at multiple scales is important to understand potential biological thermal responses to management.   Using 5 years of pre-harvest and 3 years of post-harvest stream temperature data collected in 15 small non-fish basins and 4 large fish-bearing basins we examine local and downstream temperature response to timber harvest.  Our results indicate that temperature response in the small basins varied by the level of canopy retention.  Small basins with no overstory retention and low post-harvest slash accumulations had the greatest temperature response as did a small basin with minimal overstory retention but with several beaver ponds.  While some of small headwater basins exhibited a local temperature response, it appears to be rapidly attenuated in the downstream direction and was not observable in the focused fish-monitoring reaches.