Recovery of a Louisiana barrier island marsh plant community following extensive hurricane-induced overwash

The Isles Dernieres barrier island chain provides the front line of protect ion for the Lower Terrebonne Estuary, Louisiana. Landfall of Hurricane Andr ew on August 26, 1992 resulted in overwash of most of this island chain, th ereby accelerating the erosional processes and altering the plant communiti es of the islands. Four zones were identified by the depth of overwash sand s received (from >50 cm to <10 cm) to examine the factors affecting the col onization of vegetation following overwash. Within each, zone a permanent t ransect and thirty permanent plots were established and sampled four times over two years for biotic and abiotic variables. A total of 32 plant specie s was identified, 30 of which were located in the zone with the highest loa dings of sand. Over time this zone also had the greatest increases in speci es richness. The most important survivor and early colonizer of the high zo ne overwash was Spartina alterniflora. However, over time Spartina patens b ecame dominant. The other zones, receiving moderate to no sand deposits, di ffered greatly. The few species present in these zones (<7) were indicative of high salt marsh and salt pan habitats and were dominated by Spartina al terniflora throughout the study. Using multivariate analyses, biotic and ab iotic variables were correlated. The soil variables representative of topog raphical elevation and soil salinity influenced plant community zonations o n the Isles Dernieres. Soil fertility and herbivory were not dominant facto rs affecting vegetation establishment. Backbarrier marsh areas that receive d the greatest sand loadings are now characterized by dune and swale plant species, while areas that received low sand loadings are returning to a mar sh community.