Microsite Influences on Productivity and Nutrient Circulation Within Two Southeastern Floodplain Forests

Abstract

At broad spatial scales, floodplain forests of the southeastern USA are often perceived as either nutrient poor or nutrient rich. Perceived differences in nutrient availabilities between oligotrophic blackwater and eutrophic redwater floodplain forests suggest rates of aboveground net primary production (ANPP) are lower on the former. However, for these floodplain types, microsite variation may influence relationships between nutrient circulation and ANPP to a greater extent than landscape position and geomorphology of their associated watershed. Therefore, our objectives were to compare ANPP, nutrient circulation through litterfall and decomposition, and the microbial biomass among microsites that differed in terms of soils and hydrology within two riverine floodplain forests. The two floodplains used in this study were located along the Satilla River, a Coastal Plain blackwater system, and the Altamaha River, a Piedmont redwater system, both of which are located in southeastern Georgia. Microsite influences on ANPP were not significantly different during 1999 and 2000 for the Satilla (SAT) and Altamaha (ALT) floodplains. Litterfall production and patterns of P and Ca circulation on the SAT floodplain were significantly lower for the driest microsite type during both years. Microbial biomass N and P were also lowest for the driest microsite, especially in 2000. Overall, microsites on the SAT displayed greater variation in P and Ca cycling than did those of the ALT. Litterfall production, nutrient circulation in litterfall and decomposition, and the microbial biomass were similar among microsites of the ALT floodplain during both years. These findings suggest that spatial variability in nutrient cycling may be greater for oligotrophic floodplain forests.