The relative importance of surrounding riparian vegetation and substrate composition on invertebrate community structure was investigated in six streams in Oregon, USA. We found that canopy type was more important than substrate character in influencing total abundance and guild structure. Streams without shading had higher abundances of invertebrates than did shaded steams. Most guilds were influenced by qualitative differences in food availability rather than quantity of food or substrate composition. Open streams had higher abundances in the collector—gatherer, filter feeder, herbivore shredder and piercer, and predator guilds. Contrary to expectations, shredders were no more abundant in shaded streams than in streams lacking a riparian canopy. Scraper density was inversely related to standing crop of aufwuchs, but biomass was positively correlated with quantity of aufwuchs. Examination of dominance—diversity curves showed that both canopy and substrate influenced ranked abundances of taxa, but neither canopy nor substrate strongly influenced number of taxa. Differences in community structure were not always revealed by analysis of community—level properties, although differences in both the absolute and relative abundances of individual taxa were observed.

Assemblages of aquatic vertebrate and insect predators were inventoried in streams in old-growth and logged coniferous forests in the western Cascades of Oregon to assess effects of clear-cut logging on stream communities. Effects associated with logging depended on stream size, gradient, and time after harvest. Clear-cut sections where the stream was still exposed to sunlight (5–17 yr after logging) generally had greater biomass, density, and species richness of predators than old-growth (> 450-yr-old) forested sections. Increases were greatest in small (first-order), high gradient (10–16%) streams, where clear-cut sites had both greater periphyton production and coarser streambed sediment than old-growth sites of similar size and gradient. Effects on predators were mixed in larger, lower gradient streams, where clear-cut sites showed accumulation of sediment and relatively small increases in periphyton production. Second-growth logged sections (12–35 yr after logging), reshaded by deciduous forest canopy, had lower biomass of trout and fewer predator taxa than old-growth sites.Key words: trout, salamanders, insects, logging, sediment, periphyton, watershed management

Relationships between density of fish and salamanders, riparian canopy, and physical habitat were investigated by studying 10 pairs of streams. Among vertebrate taxa, salmonids and sculpins were more abundant in streams without riparian shading than in shaded streams. Abundance of salamanders was not affected by canopy type. Densities of both salamanders and sculpins were correlated with substrate composition, whereas salmonid abundance was not or only weakly so. Salamanders were found only at high-gradient sites with coarse substrates, and sculpins were most abundant at lower-gradient sites with finer-sized sediments. An interaction was observed between the influence of canopy and that of physical setting on density of both invertebrate prey and total vertebrates. Among shaded sites, densities decreased as percent fine sediment increased, but a similar relationship did not exist among open sites. Removal of the riparian vegetation surrounding a stream may therefore mask detrimental effects of fine sediment. These data provide one reason why it has been difficult in the past to generalize about the effects of fine sediment on stream biota.

Natural rates of input and depletion of large woody debris (LWD) in southeast Alaska streams were studied to provide a basis for managing streamside zones to maintain LWD for fish habitat after timber harvest. Debris was inventoried in a variety of stream types in undisturbed old‐growth forest; 252 pieces of LWD were dated from the age of trees growing on them. Longevity of LWD was directly related to bole diameter: small LWD (10–30 cm in diameter) was less than 110 years old, whereas large LWD (>60 cm in diameter) was up to 226 years old. Assuming equilibrium between input and depletion of LWD in streams in old‐growth forests and exponential decay of LWD, we calculated input and depletion rates from mean age of LWD. Input and depletion rates were inversely proportional to LWD diameter and ranged from 1%/year for large LWD in all stream types to 3%/year for small LWD in large, high‐energy, bedrock‐controlled streams. A model of changes in LWD after timber harvest (which accounted for depletion of LWD and input from second‐growth forest) indicated that 90 years after clear‐cut logging without a stream‐side buffer strip large LWD would be reduced by 70% and recovery to prelogging levels would take more than 250 years. Because nearly all LWD is derived from within 30 m of the stream, the use of a 30‐m wide, unlogged buffer strip along both sides of the stream during timber harvest should maintain LWD.