Belowground Nutrient Dynamics Following Three Harvest Intensities on the Pearl River Floodplain , Mississippi

T HRoumouT THE USA, riverine systems represent the largest facet of forested wetlands. It is estimated that these forests cover between 6 to 13 million hectares in the U.S. Southeast (Sharitz and Mitsch, 1993). Because of their position at the land-water interface, these ecosystems are active biogeochemically since they buffer impacts from upland areas while also interacting with the floodwaters that pass across the floodplain. Since these ecosystems cover a broad land base, forested floodplains are also valuable sources of timber, and thus forest management activities are a significant anthropo-genie disturbance in these ecosystems. Little information exists regarding the impacts of forest management practices on the biogeochemical processes within floodplain forests. Even less is known about harvesting impacts on belowground processes within these ecosystems, especially the processes controlling labile C pools and nutrient cycling. Developing a better understanding of these impacts is critical, since belowground processes ultimately determine site productivity and ecological function. and abundance are important since organic matter acts as both a source and sink for soil C (Henderson, 1995). Within forested ecosystems, net primary production is related to the amount and depth of soil organic matter, while the quantity of organic matter within the soil is balanced between levels of net primary production and decomposition rates (Paul and Clark, 1996). Thus, changing levels of above-and belowground net primary production as well as mineralization-immobilization patterns will ultimately influence source-sink relationships within these ecosystems. Fine roots are an important mechanism controlling labile C and nutrient pools in forested ecosystems (Na-delhoffer et al., 1985; Hendrick and Pregitzer, 1996). These pools are partially dependent upon belowground inputs from forest vegetation; thus changing fine root production levels as a result of timber removal may alter levels of belowground net primary production within these ecosystems. Since belowground net primary production is a significant portion of total net primary production (Vogt et al., 1986), changes to the levels of fine root production and biomass as a result of forest management practices may ultimately influence long-term nutrient levels in forest soils. Forest soils are a major long-term C source, and possibly the principal C sink in undisturbed terrestrial ecosystems (Harrison et al., 1995). To date, a detailed understanding of the influences of harvesting practices on levels of COz efflux remains unclear Within undisturbed floodplain forests, detrital C processing is strongly influenced by aerobic respiration (Pulliam, 1993); however, few studies have examined the influences of different …