Effects of beaver damn on invertebrate drift in forest streams

We aimed to assess the effects of beaver dams on the invertebrate drift fauna in five central Swedish boreal forest streams. Each stream was sampled once during the autumn, with drift traps placed upstream and downstream of the beaver dams. Drift densities (numbers/100 m(3) water) were calculated. The invertebrates were determined, dried and weighed. No significant differences were noted in total drift densities or in the drift densities of pelagic species. The drift densities of benthic species were higher upstream of the dam, mainly because Ephemeroptera were more abundant in the upstream part. No significant difference was observed in diversity or dry weight. The functional feeding group ratio: filtering collectors/gathering collectors was significantly higher downstream of the dam.