The role of environmental variables on interannual variation in species composition and biomass in a subtropical minerotrophic floating marsh

Floating marshes supporting emergent vascular vegetation occur in expansive areas in many parts of the world. We analyzed the long-term variability in species composition and related plant biomass to environmental variables in a subtropical minerotrophic floating marsh, Louisiana, U.S.A. Panicum hemitomon was the dominant plant species, representing 76% of the total mean end of season aboveground dry weight of 840 g∙m−2. Multivariate analyses showed that community structure in the Lake Boeuf floating marsh has changed little during the 11 years included in this study. Individual species occurring in varying frequency with the dominant, Panicum hemitomon, form two marginally distinct assemblages. Mean live end of season biomass varied from a low of 602 g dry wt∙m−2 to a high of 1173 g dry wt∙m−2 during the period of the study. Ninety-nine percent of the variation in total aboveground biomass can be predicted by environmental variables related to temperature, precipitation, evaporation, and water level. Mapping of the area for the years 1945, 1952, 1981, and 1992 show that a net loss of about 4% of marsh has occurred between 1945 and 1992.