Effects of canopy modification and accumulated sediment on stream communities

Small streams differing in sediment composition were compared in logged arid forested reach-es to determine effects of accumulated fine sediment on stream communities under differenttrophic conditions. Three stages of forest community succession were studied in the CascadeMountains: 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 coniferousforest (>450 years old). One stream with mostly coarse sediment (56-76% cobble) and one withmore fine sediment (5-14% sand and 23-53% gravel) were contrasted for each successionalstage. 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 didthe shaded, forested sites regardless of sediment composition. We conclude that for these smallCascade Range streams, changes in trophic status and increased primary productivity resultingfrom shade removal may mask or override effects of sedimentation.