Effects of streamside riparian forest management on Ephemeroptera and Trichoptera community structure in four western Oregon streams Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/tq57nt948

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  • In order to restore conifers in hardwood dominated riparian forests 25% of the experimental reach forests alongside four streams in western Oregon was clearcut. Clearcutting removed 400 m without residual buffers from a 1600-m streamside forest reach in patchcuts spanning 100 and 200 meters. To assess the cumulative and direct effects of the 25% removal on the biotic stream community, Ephemeroptera (mayflies) nymphs and Trichoptera (caddisfiies) larvae were sampled on each stream under the buffered and exposed reaches. Samples were collected using a Surber sampler at four locations during the summers of 1993 and 1994, and identified by genus and functional feeding group. Absolute and relative abundance of genera and functional feeding groups and the Shannon-Wiener diversity index were calculated to compare community responses between sample sites. Insects from three untreated reference streams were also analyzed to compare natural versus treated community variability. Spatially, genera generally increased in abundance midway through the 25% clearcut reach. Specific genera, including Baetis, Glossosoma, and Micrasema, increased in the exposed clearcut. Collector-gatherers and scrapers also increased in the exposed reach and collector-filterers peaked below the 200-m patchcut. Shredders and predators did not show significant differences either year. Temporally, more individual taxa as well as the diversity index increased the second year after treatments. However, reference stream data indicated that even on untreated streams there is background variability among congeners at different sampling points and in different sampling years. Yearly differences in diversity were likely within the range of normal community variability. The responses of treated stream genera, however, greatly exceeded the few changes in population observed on the reference streams. Therefore, increases and/or decreases in abundance both years may be assumed to be a response to localized harvesting treatment effects. Treatment effects, however, occurred primarily in mid-reach. Genera increases spanned short longitudinal distances and most taxa and functional feeding groups had returned to reference levels at the bottom of the 1600-m reach. The total 25% harvest removal did not appear to influence the mayfly and caddisfly absolute and relative abundance, functional feeding groups, or diversity on these four western Oregon streams other than locally.
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