Succession of Vegetation in an Evolving River Delta, Atchafalaya Bay, Louisiana

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Abstract
(1) A description is given of the wetland vegetation on the natural islands of the Atchafalaya Delta, Louisiana. (2) The vegetation was described using principal components analysis, which allowed an objective classification of the community into species associations. Seasonal change in each association was described by comparing the community data from spring and autumn samplings. Relationships between the vegetation groups and environmental characteristics were evaluated. (3) Three vegetation associations explained the most variance in the spring and autumn analyses and also occupied the greatest area. Each was dominated by a single species: Sagittaria latifolia, Salix nigra or Typha latifolia. In each of these associations diversity was low. Measurement of the similarity in species composition among the main associations showed little spatial overlap among them. More complex seasonally-changing plant associations, with higher diversity and greater spatial overlap, are developing on the delta islands, but at present occupy little area. (4) Analysis of soil nutrients revealed little variation with season or plant association. In contrast, the percentage variation in water level, organic carbon, and percentage sand with season and plant association was substantial. Hydrologic influences on the delta islands seem to have the greatest influence on the distribution of vegetation.