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Responses of macroinvertebrate community composition to changes in stream abiotic factors after streamside clear-cut logging in the central interior of British Columbia Fuchs, Shirley A.

Abstract

Effects of a clear-cut timber harvest of the riparian zone were studied on 18 stream systems in watersheds influenced by a continental climate regime in the central interior of British Columbia. Streams selected in the Stuart-Takla and Willow-Bowron watersheds were sampled between mid-September and late October 1995. Study streams were classified according to stages of clear-cut harvest in the riparian zone: streams within unharvested reaches, streams without canopy cover (timber harvest less than 5 years old) or streams with a deciduous canopy cover (timber harvest more than 20 years old). Measurements were taken of topographic and habitat attributes, of watersheds and productivity and the benthic macroinvertebrate community. 'Uncut' stream channels had higher gradients and narrower widths than were found in 'old cut' streams suggesting that stream channel dimensions of streams in logged areas may have changed over time. More specifically, 'recent cut' streams had the lowest canopy cover and the highest chlorophyll α biomass. However, in 'old cut' streams with dense canopy cover, chlorophyll α biomass was similar to levels in 'uncut' streams. In addition, although density of benthic macroinvertebrates did not appear to have changed over time, total biomass increased soon after timber harvest. After more than 20 years, biomass measurements of macroinvertebrates were similar to levels found in unharvested streams. Density and biomass of the scraper functional guild, in particular, were lowest in 'recent cut' streams. These streams also had the highest densities of predators and invertebrate parasites and the highest biomass of collector functional guilds and leeches. Higher biomass of the two collector guilds in 'recent cut' streams may have been linked to an increase in the quality of their food source, i.e., FPOM, although this was not measured in this study. Higher biomass of scrapers and collectors found soon after the timber harvest may have attracted resident fish into these streams, and so increased fish parasite biomass. After more than 20 years following timber harvest, biotic and abiotic factors may have returned to levels found prior to timber harvests. Future work is required to determine the factors that influence changes in benthic community composition and instream habitat in stream ecosystems following timber harvest in this region.

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