Effects of forest defoliation by the gypsy moth on detritus processing in southern Appalachian streams

We investigated whether changes in chestnut oak (Quercus prinus L.) leaf qu ality caused by gypsy moth (Lymantria dispar L.) defoliation affected leaf breakdown rates in southern Appalachian streams of differing disturbance hi story. Breakdown rates of second-flush leaves produced after defoliation we re compared to those of natural spring-flush leaves shed in autumn. Second- flush leaves broke down significantly faster than spring-flush leaves in th ree of the six streams tested. Initial fiber content and the ratio of fiber to protein were significantly higher in spring-flush leaves than in second -flush leaves, showing that initial differences in internal leaf constituen ts could explain the faster breakdown rates of second-flush leaves. Using c hanges in leaf toughness through time as a measure of microbial conditionin g we found that the faster-decaying second-flush leaves also softened at a faster rate than the spring-flush leaves. In addition, both types of leaves incubated in three streams draining a recovering 14-y-old clear-cut catchm ent broke down significantly faster than leaves incubated in three streams draining a reference catchment. We attributed this increase in leaf breakdo wn to significantly higher abundance and density of leaf-shredding insects and greater microbial conditioning in leaf packs in the streams of the reco vering clear-cut catchment. Overall, our results show that insect defoliati on accelerates detritus processing in southern Appalachian streams and that this acceleration may be especially important in previously disturbed stre ams in which leaves are already processed faster.