SPECIES ASSOCIATION CHANGES ACROSS A GRADIENT OF FRESH-WATER, OLIGOHALINE, AND MESOHALINE TIDAL MARSHES ALONG THE LOWER SAVANNA RIVER

In the present study, plant species patterns and associated environmen tal factors of freshwater, oligohaline, and mesohaline marshes of the Savannah National Wildlife Refuge were compared. DECORANA, an ordinati on method, was used to group vegetation classes. Discriminant function analysis was applied to resulting classes to quantify differences in salinity, elevation, and distance from tidal channels among classes. N ine vegetation classes across freshwater and brackish marshes correspo nded significantly to salinity differences between sites. Combinations of elevation and distance from tidal channel were significant in sepa rating vegetation classes within sites. Scirpus validus (Vahl) was the only species to occur over the entire range of measured physical para meters and accounted for much of the overlap between vegetation classe s. The proportion of correctly classified vegetation classes between s ites;was 70%. Within each site, the proportion of correct classificati on was lower in the freshwater marsh (77% correct classifications) whe n compared with the oligohaline (82%), strongly oligohaline (83%), and mesohaline (85%) sites. Although overlap among classes was greater in the more diverse freshwater marsh, our results may reflect difference s in the steepness of environmental gradients between sites and the sc ale at which physical parameters were measured rather than actual plan t distribution overlap. Results suggest that resources are more finely divided among species in the freshwater marsh, resulting in a less di stinct dominance hierarchy when compared with the mesohaline marsh.