Shifts In Aquatic Insect Populations In A First-Order Southern Appalachian Stream Following A Decade Of Old Field Succession

Abstract

Aquatic insects of two first-order southern Appalachian streams were sampled monthly during one year. Sawmill Branch Watershed was subjected to several disturbances before 1968, including clear-cutting. Since 1968 Sawmill Branch Watershed has undergone natural secondary succession from terrestrial vegetation dominated by Gramineae to a herbaceous/coppice hardwood dominated by black locust, Robinia pseudoacacia. Grady Branch, the control stream, drains an undisturbed hardwood watershed. Aquatic insect densities on Sawmill Branch were about twice those of Grady Branch, which represent a dramatic reversal from results obtained by a similar study in 1968. It is suggested that change in riparian vegetation is a major factor influencing long-term changes in aquatic insect populations, and these changes are manifested through a shift toward an allochthonous energy base. The most conspicuous changes in macrobenthos on the disturbed watershed between 1968 and 1978 were a reduction in grazer organisms and a corresponding increase in shredder organisms, especially Peltoperla (Plecoptera).Key words: macrobenthos, secondary succession, watershed changes, clear-cutting, allochthonous detritus, food quality.