Abstract
Forest practices (e.g. timber harvest, road construction, etc.) remain a major anthropogenic influence in many forested watersheds. To minimize adverse effects of forest practices on fish communities, forest practice regulations (riparian buffers, limit size of harvest units, erosion control) have been developed in recent decades. As the top of aquatic food webs, response of resident fish populations provides a key indicator of the effects of forest practices on aquatic ecosystems. To evaluate effects of forest practices on fish, a comprehensive nested and paired before-after, control-impact (BACI) study was implemented in the Mica Creek Experimental Watershed (MCEW), Idaho, USA. Fish populations including native westslope cutthroat trout (Oncorhynchus clarkii lewisi), non-native brook trout (Salvelinus fontinalis), and sculpin species (Cottidae spp.) were monitored for 7 years pre- and 6 years post-harvest. Relative to reference and pre-treatment relationships age 1+ salmonid densities (as first pass capture, removal estimates, and density) significantly increased post-harvest in the rotation clearcut, thinning (partial cut), and upstream cumulative (∼0.9 km downstream) reach, but did not vary in the downstream cumulative (∼3.8 km downstream) reach. Estimated increases in salmonid densities ranged from + 41% in the upstream cumulative reach to + 156% in the rotation clearcut reach. Both non-native brook trout and native westslope cutthroat trout densities increased post-harvest suggesting both species contributed to the overall salmonid response. Sculpin densities did not vary significantly with harvest treatment. Continued monitoring will help evaluate fish responses during stand regrowth, hydrologic recovery, and additional forest practices as the MCEW transitions to a 21st century working forestland watershed.