The role of forest debris in a southeastern stream and the effects of its removal on trout populations

Measurements of substrate composition, cover characteristics, and trout populations and biomass were made at a total of ten sites on South Fork Mills River and one of its tributaries. Poplar Creek, in 1975 and 1976.

Besides providing cover debris accumulations generally caused a reduction in stream velocity with accompanying deposition of smaller substrate types. Removal of debris caused a shift to larger substrates.

A multiple regression treatment of the physical characteristics and trout populations indicated that regression models relating the presence of debris and large substrates (interpreted here as increasing water flow) to trout populations were the only ones significant at the .1 level and accounted for 58% of the variation in trout biomass. The presence of debris could account for none of the variations in trout numbers. Areas containing debris were found to contain populations made up of larger fish than areas without debris.

The effects of debris removal were not clear cut, however, there was a trend towards reduced biomass but not necessarily reduced number of trout. This was probably due to decreases in cover, which made the areas less desirable for large trout, but increased flows which favored smaller trout.