The effect of riparian condition on invertebrate drift in mountain streams

Abstract

The effect of stream riparian condition on invertebrate drift was examined in headwater streams of the Torpy River in north-central British Columbia, Canada. Forest harvesting provided the opportunity to examine drift within control streams (i.e., within intact forest), streams with 10 m foliated reserve strips, streams with 10 m defoliated riparian reserve strips, and streams without riparian reserve strips (i.e., clear cut to the stream bank). The density (concentration) of aquatic invertebrates (individuals m−3) in the drift was significantly lower in streams with 10 m riparian reserves compared to control streams (P 10 m defoliated > 10 m foliated). There was significantly more aquatic drift in downstream vs. upstream locations of control streams, but this pattern was reversed for harvested streams (P = 0.51) leading to a significant interaction term in the analysis (P = 0.046; which indicates that the upstream-downstream comparison differed significantly between control and treatment streams in this double-control design). These types of changes in the drift of aquatic and terrestrial invertebrates are known to affect stream ecosystems through trophic interactions among periphyton, benthic grazers, and fish. Consequently, both the quantity and quality of riparian reserve strips must be considered for the effective mitigation of forestry practices.