Timber Harvest Influence on Flow Regimes and Fish in a Northern Idaho Watershed

Disturbances occur naturally in forested landscapes of western North America.  Forest management introduces an element of anthropogenic disturbance that can cause additional alterations to aquatic ecosystems within these watersheds.  Today, current regulations and contemporary timber harvest management activities using Best Management Practices (BMPs) attempt to minimize detrimental effects to stream channels through riparian buffers (stream protection zones), outsloped road construction, relief culverts near stream crossings, filter windrows, and adjacency guidelines that assist with hydrologic recovery.  To meet the needs of evaluating timber harvest response, a comprehensive nested and paired Before-After-Control-Impact (BACI) design was implemented in the Mica Creek Experimental Watershed (MCEW) in northern Idaho, which is privately owned by Potlatch Corporation.  In addition to evaluating abiotic responses like streamflow, monitoring was also conducted to evaluate biotic responses, including fish abundance and species composition.  Salmonid populations present in this study were native westslope cutthroat (Oncorhynchus clarki lewisi) and non-native brook trout (Salvelinus fontinalis).  Following harvest, overall streamflow increased by 36 percent in the clearcut catchment and by 23 percent in the partial-cut catchment.  Increases in streamflow (11-20 percent) were also observed at downstream cumulative monitoring sites.  Post-harvest data indicated overall fish abundance increased immediately following timber harvest.  Westslope cutthroat numbers remained relatively stable following harvest, while invasive brook trout numbers increased.  While the linkage of these results don’t address all the causal effects of physical alterations to biotic communities, it does improve our broader understanding of 21^st century forest management practices on small mountain stream flow regimes and fish communities.