Simulated fate of leaf litter and large woody debris at a riparian cutbank

Abstract

Leaf litter and woody debris are important sources of carbon for stream ecosystems, but the patterns of such inputs are variable. To clarify the processes that may lead to such variations, we modified a computer simulation model of forest dynamics to record the production, transport, and decomposition of leaf litter and woody debris given conditions found on a floodplain. The species chosen represent those of floodplains in the central Mississippi River valley, United States. We examined differences in model results when the conditions simulated were (i) a floodplain forest interior or a riparian cutbank edge, (ii) high or low flood regimes, and (iii) with or without the direct removal of material by flood flows. Projections of productivity of floodplain interior sites were similar to those observed in other studies in comparable areas. The inclusion of edge effects increased litter and debris production significantly. There were differences in how material produced was apportioned: there was a greater input to the river that had edge effects and, trivially, flood removal; there was greater on-site storage otherwise. Interaction effects were found because of the dependence on initial productivity. This simulation indicates that the particular local effects of hydrological and geomorphological processes will affect the fate of carbon on floodplains and reveals the importance of a spatially explicit conceptualization of forest dynamics.