Large woody debris in a headwater stream: Long-term legacies of forest disturbance

We excluded litter (leaves and wood) inputs to an Appalachian headwater str eam for 5 years. Leaves disappeared from the streambed very rapidly (< 1 ye ar) following litter exclusion, however, a large residual mass of woody deb ris remained. After excluding inputs of leaf litter and wood to the stream for 3 years we removed all small wood (< 10 cm diameter) from the stream. T here was close agreement (within 10%) between estimates of mass of small wo ody debris made using line intersect methods and that made by direct remova l. Two years later, we removed all large woody debris (LWD = > 10 cm diamet er) from the wetted perimeter of the stream. Five annual estimates of LWD m ass made with line intersect methods exceeded those of complete removal by a factor of about 2x, although total wood removed was within the 95% confid ence interval of that estimated by the line intersect method. Species of wo od removed from the stream displayed weak similarity (percent similarity = 45 to 49%) with recent (1993 and 1972) measures of basal area of tree speci es in the surrounding forest, but stronger similarity (65%) with tree speci es measured in 1934. About 37% of the LWD removed consisted of American che stnut, Castanea dentata, (similar to 24%) and black locust, Robinia pseudoa cacia, (similar to 14%), which currently represent < 1.5% of the basal area of the surrounding forest. LWD in the stream reflects large inputs of ches tnut following the chestnut blight in the 1930s and inputs of early success ional species such as black locust following extensive timber harvesting in the early 1920s. These earlier disturbances to the forest were important s ources of LWD that remain in the stream today. Thus, the structure and func tion of present day streams are influenced by forest disturbances that occu rred over six decades ago.