Influence of forest practices on aquatic production

Management of streamsides for fishery resources requiresa thorough knowledge of the structure and major processes of streamecosystems. Management of streamside forests must be based on afunctional perspective of riparian zones that integrates geomorphicprocesses, terrestrial plant succession, and aquatic ecology. Forestrypractices pbtentially alter solar radiation, water temperature, sediment,nutrient, and litter inputs, woody debris, and channel structure--all ofwhich influence the habitat and nutritional resources of aquatic organ-isms. Primary producers are generally stimulated by canopy removal andthe increases in nutrients and temperature that often accompany timberharvest, but instability of stream sediments may decrease plant abun-dance. Microbial processes may be enhanced by increases in nutrients,detrital quality, and temperature, but microorganisms may be negative-ly affected by a decreased quantity of detritus or decreased oxygenconcentrations. The ability of streams to retain algae and litter inputsfor food resources and retain sediments for habitat is determined bychannel complexity, especially accumulations of woody debris. Aquaticinsects and other invertebrates respond to changes in habitat and foodresources. Sedimentation and decreased substrate stability may decreasethe abundance of aquatic insects. Herbivores benefit from stimulation ofaquatic plants; detritivores may be negatively affected by the changesin detritus. Frequently, insect community structure shifts towardorganisms that are more likely to drift, thereby increasing the avail-ability of food for salmonids. Salmonids also more efficiently captureprey items in open areas where light intensities are greater. Thesepotential benefits may be negated if thermal tolerances are exceededby temperature increases, if sediments blanket rearing and spawninghabitat, or if winter habitat is reduced. Changes in habitat, food, ortemperature may also alter fish community structure and potentiallyincrease competition with the species of interest.
Streams in harvested watersheds may therefore be more pro-ductive, but the abundance and distribution of organisms in thesestreams may fluctuate more than in streams in mature forests. ResourceObjectives must be clearly defined before fishery resources can beeffectively managed in forest ecosystems. The landscapes and bioticcommunities of terrestrial and aquatic ecosystems are intricately linked,
d effective management must acknowledge and incorporate suchcomplexity.