Responses of invertebrates and algae of a boreal coniferous forest stream to experimental manipulation of leaf litter inputs and shading

Forest harvesting alters leaf litter inputs and shading of small streams. Most of the previous studies of harvesting effects are limited to coastal or deciduous forests, so here we consider a sub-boreal forest stream. To test the hypothesis that changes in light and litter inputs would affect the benthic community in these streams, we experimentally manipulated these variables in stream mesocosms. We used a 2 × 2 factorial design with light (shaded or full light) and leaf litter inputs (equivalent to a forested stream or one quarter that rate) as factors. The high leaf litter treatment resulted in differences in macroinvertebrate community composition and higher densities of two shredders, Limnephilus sp. and Podmosta sp., suggesting food limitation. Algal filaments were longer in the high light treatments indicating a change in periphyton composition. There were no significant differences in chlorophyll a or ash-free dry mass, suggesting that light was not limiting to periphyton. The community structure clearly shifted in response to both resources, although primarily to detrital inputs. These results provide evidence that changes to shading and leaf inputs to small streams can affect the benthos and may limit secondary production.