Most studies of stream wood have focused on pieces a parts per thousand yen0.1 m diameter. However, this approach may overlook an important feature of small streams, where wood < 0.1 m can constitute the majority of wood pieces. We examined the effect of fine wood (FW) on local drift of stream macroinvertebrates. The study was carried out at seven sites in four boreal forest streams, from early June to mid-August 2011. This was done by anchoring bundles of FW at each site and measuring drift upstream and downstream of each bundle. We hypothesized that FW would increase drift density, biomass and diversity of aquatic invertebrates. Ten weeks after FW addition, aquatic drift density was higher downstream than upstream of FW bundles, while drift biomass and drift diversity did not differ significantly downstream and upstream of FW.

Changes in riparian vegetation due to forest harvesting may affect the input of fine woody debris, an important structural element, to streams. Woody debris has been shown to benefit trout populations. In-stream fine woody debris (FWD) has not been studied as extensively as large woody debris, but is probably important to smaller-sized trout. In a laboratory stream experiment we tested young-of-the-year wild brown trout, Salmo trutta, responses to three densities of fine woody debris (FWD). The trout were tested as singletons and four together. Swimming activity increased with increasing fish density and decreasing FWD density. Foraging decreased and time spent in FWD increased with increasing FWD density. Aggressiveness was lowest in intermediate FWD density. Our study shows that FWD impact on trout is related to fish rank, fish density and FWD density, and that juvenile trout response to fine WD is different from the response to large WD reported by others.