Long-term patterns in leaf breakdown in streams in response to watershed logging

The watershed of Big Hurricane Branch, Coweeta Hydrologic Laboratory, North Carolina, USA, was logged in 1976. We measured breakdown rates of experime ntal leaf packs in this second-order stream prior to logging, during loggin g, soon after logging, and 3 additional times since then. Leaf breakdown wa s slow just after logging, apparently due to leaf burial by sediments. Ther eafter, leaf breakdown rates have been consistently faster than before logg ing 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 ti mes higher than in a reference stream. The high nutrient concentration may be stimulating microbial decomposition processes in leaf packs. Second, dom inance of litterfall by "medium" and "fast" processing leaves from the reco vering 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 inve rtebrates whose feeding activities may also hasten the breakdown rates.