Temporal changes in the vegetation pattern in a tidal freshwater marsh

Temporal changes in vegetation patterns of Chesapeake Bay wetlands have been poorly documented. Data from a 1987 vegetation analysis of a Chesapeake Bay tidal freshwater marsh were compared to those of a vegetation study completed in 1974. Changes in the vegetation pattern were calculated using species importance values and a species diversity index. Comparison of the 1987 and 1974 results shows no significant difference in species diversity index. However, there was a significant difference in species contribution to the index. Spartina cynosuroides, an oligohaline species that was not among the dominant species listed in the 1974 study, had the fourth highest importance value in this study. The change in dominant species composition of the marsh may reflect a directional shift from tidal freshwater toward oligohaline conditions.