Substrate‐Mediated Response of Stream Invertebrates to Disturbance

The response of aquatic invertebrates to a major watershed (catchment) disturbance, clear—cutting, was examined in a second—order stream in the southern Appalachian Mountains. For 21 mo after the start of logging, invertebrates were sampled in four substrate types: rock face (moss—covered boulders and outcrops), cobble riffles, pebble riffles, and sand. The type of substrate was an important factor in determining the direction and magnitude of the response of many taxa. In the stream that drained the clear—cut watershed, more taxa increased in density (compared with a nearby reference stream) in moss—covered rock face than in any other substrate; cobble riffles were next, followed by pebble riffles and sand. Conversely, the number of taxa with significant reductions in density was highest for sand substrates, followed by pebble, cobble, and rock face. Among functional groups of insects, collector—gatherers and scrapers increased, while the dominant shredder, Peltoperla, declined. The differential response of invertebrates among substrates suggests that biological stability is closely coupled with physical stability; however, moss associated with larger particles may be a factor in enhancing the biological stability of these substrates. Clear—cutting of a watershed is a largescale, low—frequency, anthropogenic disturbance to associated stream ecosystems. Certain successional characteristics of these headwater streams following a major anthropogenic disturbance differ from those observed in streams in which succession may be truncated by frequent disturbances such as flash flooding.