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

Abstract

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. Key words: vegetation, stability, freshwater floating marsh, Panicum hemitomon, Louisiana, climate.

Floating mats: their occurrence and influence on shoreline distribution of emergent vegetation

“…Furthermore, there is no consensus in the literature on the ecological significance of floating emergent mats. Floating‐mat communities have been variously described as a stage in the succession from open water to dry land (Sculthorpe, 1967), an endpoint in succession characterised by remarkable stability in community structure (Sasser et al. , 1995) and as an illustration of the adaptation by rhizomatous plants to problems of fluctuating water level (Keddy, 2000).…”

Long-term vegetation change in Louisiana tidal marshes, 1968–1992

“…However, 92 percent of the maidencane marshes in Terrebonne estuary are floating (Evers et al 1996). Although attached Panicum hemitomon is negatively affected by increased water levels (McKee and Mendelssohn 1989), floating Panicum hemitomon biomass is positively correlated with higher water levels (Sasser et al 1995b). The positive effect of increased water level on floating Panicum hemitomon is presumably due to higher nutrient levels associated with increased runoff (Sasser et al 1995b).…”

“…Although attached Panicum hemitomon is negatively affected by increased water levels (McKee and Mendelssohn 1989), floating Panicum hemitomon biomass is positively correlated with higher water levels (Sasser et al 1995b). The positive effect of increased water level on floating Panicum hemitomon is presumably due to higher nutrient levels associated with increased runoff (Sasser et al 1995b). In addition, based on 1990 imagery, fresh spikerush marsh has also started to appear in Barataria estuary (Sasser et al 1994, Evers et al 1996.…”

Floating islands in a tropical wetland of peninsular India

“…Such floating mats have been called floating islands or sudds (Pallis 1915;Kashyap 1920;Sahni 1927;Russel 1942;Reid 1952;Lind 1956;Kaul and Zutshi 1966;Sculthorpe 1967;Little 1969;Junk 1970Junk , 1973Junk , 1977Scutcliffe 1974;Varfolomeyeva 1977;Sasser et al 1995Sasser et al , 1996Mitsch and Gosselink 2000;Mallison et al 2001;Adams et al 2002;Gopal et al 2003;Azza et al 2006). They represent a special habitat different from their surrounding water-spread.…”

“…They provide more space and habitat for emergent plants, facilitating their spread into the open water. These are described variously as a stage in the succession from open water to dry land (Sculthorpe 1967), an end point in succession characterised by remarkable stability in community structure (Sasser et al 1995) and as an adaptation by rhizomatous plants to problems of fluctuating water level (Keddy 2000;Azza et al 2006). Large floating islands often disturb the submerged and floating leaved vegetation to a great extent by cutting off light and oxygen.…”