Effects of Canopy Modification and Accumulated Sediment on Stream Communities

Abstract

Small streams differing in sediment composition were compared in logged and forested reaches to determine effects of accumulated fine sediment on stream communities under different trophic conditions. Three stages of forest community succession were studied in the Cascade Mountains: Recently clear-cut areas without forest canopy (5–10 years after logging); second-growth forest with deciduous canopy (30–40 years after logging); and old-growth coniferous forest (>450 years old). One stream with mostly coarse sediment (56–76% cobble) and one with more fine sediment (5–14% sand and 23–53% gravel) were contrasted for each successional stage. In general, streams traversing open clear-cuts had greater rates of microbial respiration, and greater densities or biomasses of aufwuchs, benthos, drift, salamanders, and trout than did the shaded, forested sites regardless of sediment composition. We conclude that for these small Cascade Range streams, changes in trophic status and increased primary productivity resulting from shade removal may mask or override effects of sedimentation.