Three Long-Term Studies of Paired Watersheds Pre- and Post-Timber Harvest in Western Oregon

A BACI design was used to study three paired watersheds in western Oregon where we are examining how current-practice forestry affects benthic invertebrates, emerging aquatic insects and salmonid diet.  Preharvest we found strong differences in benthic composition between Hinkle, Alsea, and Upper Trask watersheds, but we did not detect differences among headwater tributaries within basins. Other spatial differences (headwaters vs. mainstems) in benthics, and temporal differences (annual and seasonal) in benthics, emergence and diet were also detected.  Currently, we have post-harvest results completed for Hinkle and preliminary results for Alsea and Trask watersheds. After timber harvest at fishless Hinkle Creek headwaters, local changes in benthic community composition, increases in benthic densities, in midge densities, and in aquatic insect emergence, along with decreased taxa richness were detected. After logging adjacent to mainstem reaches, effects were similar, but benthic densities did not increase. At Trask, headwater benthic community composition a year post-harvest also show local changes. To date, we cannot detect similar responses to harvest at Alsea, but responses may be more pronounced following additional harvest in summer 2014. We believe the regional scope, longevity, and within-basin replication of our studies are helping us identify both general and site-specific responses to harvest.