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 expa nsive areas in many parts of the world. We analyzed the long-term vari ability in species composition and related plant biomass to environmen tal variables in a subtropical minerotrophic floating marsh, Louisiana , U.S.A. Panicum hemitomon was the dominant plant species, representin g 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 inclu ded in this study. Individual species occurring in varying frequency w ith the dominant, Panicum hemitomon, form two marginally distinct asse mblages. Mean live end of season biomass varied from a low of 602 g dr y wt . m(-2) to a high of 1173 g dry wt . m(-2) during the period of t he study. Ninety-nine percent of the variation in total aboveground bi omass can be predicted by environmental variables related to temperatu re, precipitation, evaporation, and water level. Mapping of the area f or the years 1945, 1952, 1981, and 1992 show that a net loss of about 4% of marsh has occurred between 1945 and 1992.