We measured the effects of timber-harvest condition (clearcut and forested) and flow duration (perennial and intermittent) on emergent aquatic insect assemblages at 20 headwater streams in the Central Oregon Coast Range. Clearcut streams had been logged to the stream banks within 2 y prior to the start of our study. Adult aquatic insects were sampled from a 40-m reach at each study stream in 3 seasons: summer, autumn, and spring. Emergent insects were strong indicators of harvest condition and, regardless of flow duration or season, more aquatic insects emerged from streams in clearcut catchments than in forested catchments. Plecoptera had higher emergence rates from intermittent streams than from perennial streams in spring. Functional feeding group composition was not apparently affected by harvest condition or flow duration. Taxon richness was slightly higher at clearcut than at forested streams, primarily because of the occurrence of rare taxa at clearcut streams. Nonmetric multidimensional scaling (NMS) ordination of emergent aquatic insect assemblages showed community patterns that varied by season and harvest condition, but little by flow duration. Stream canopy % cover, stand age, logging debris (% slash), and substrate composition differed between clearcut and forested streams and were strongly correlated with NMS axes. Taxa that responded to conditions created by logging, such as % slash or canopy opening, contributed to differences in assemblages between headwater streams flowing through clearcut and forested catchments.
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Vol. 26 • No. 4