Wednesday, May 28, 2008 - 10:00 AM
387

Benthic macroinvertebrate response to multiple clear-cut forest harvest: Local habitat effects override cumulative watershed effects

Morgan Hannaford, Department of Biology, Shasta College, Redding, CA 96049 and Cajun James, Sierra Pacific Industries, Redding, CA 96049.

Cumulative watershed effects caused by clear-cut harvest management are of great concern for conservation of aquatic resources in forested streams.  Although physical and biological monitoring of stream quality is commonly done to identify cumulative watershed effects, few tests of the sensitivity of these indicators have been attempted.  As part of an experimental forest harvest, designed to measure cumulative watershed effects on a stream in Northern California, we sampled physical habitat parameters and macroinvertebrate assemblages in a series of alternating clear-cut and unharvested reaches.  Water temperature and flow cumulatively increased over the entire 3 km study reach after treatment.  Benthic macroinvertebrate indices that are popular in many biomonitoring programs (based on taxa richness, EPT, and tolerance metrics) failed to discriminate between clear-cut and unharvested reaches.  Clear-cut reaches had a greater frequency of large predatory Megaloptera and Plecoptera among other taxa that are assumed to be “sensitive” water quality indicators.   Multivariate analysis of macroinvertebrate species assemblages identified significant differences between clear-cut and unharvested reaches.  However, no cumulative longitudinal pattern of change in macroinvertebrate species assemblages was observed.  This study suggests that localized stream habitat effects have a greater influence on macroinvertebrate species assemblages than any physical cumulative watershed effects we observed.


Web Page: macroinvertebrates, clear-cut, bioassessment

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