Long-Term Patterns in Leaf Breakdown in Streams in Response to Watershed Logging

Abstract

The watershed of Big Hurricane Branch, Coweeta Hydrologic Laboratory, North Carolina, USA, was logged in 1976. We measured breakdown rates of experimental leaf packs in this second-order stream prior to logging, during logging, soon after logging, and 3 additional times since then. Leaf breakdown was slow just after logging, apparently due to leaf burial by sediments. Thereafter, leaf breakdown rates have been consistently faster than before logging and faster than in a reference stream. These differences may be related to 3 factors. First, the post-logging nitrate concentration has been about 3–10 times higher than pre-logging values in Big Hurricane Branch and 5 times higher than in a reference stream. The high nutrient concentration may be stimulating microbial decomposition processes in leaf packs. Second, dominance of litterfall by “medium” and “fast” processing leaves from the recovering forest coupled with relatively high sediment loads during storms may hasten breakdown through physical abrasion. Third, the interaction of high nutrients and high quality leaves may be attractive to leaf-shredding invertebrates whose feeding activities may also hasten the breakdown rates.