The purpose of this study was to test the hypothesis that emergent plant communities, at Marsh Island, Louisiana, were unaffected by weir management. Although weir management may affect other marshes differently than those at Marsh Island, this study may indicate how other coastal marshes respond to similar forms of minimal management. The poorly drained marsh had lower species richness and diversity than the better drained marsh, and poorly drained and better drained marshes differed in the importance of 4 major plant species. Vegetative cover, species richness, diversity index, and abundant marsh plants did not differ between weir managed and unmanaged marshes. Species composition was lower in weir managed marsh for 4 species: Lythrum lineare, Pluchea foetida, Setaria glauca, and Vigna luteola, but higher for Distichlis spicata. Spartina patens and Juncus roemerianus dominated the weir managed and unmanaged areas. When muskrats were present, nutria were usually present, but the reverse was not true. No difference was found between the weir managed marsh and unmanaged marsh in the 6 characteristics that differed between poorly drained and better drained marshes, or in any other characteristic except for Echinochloa walteri, which was more abundant in weir managed marsh. Species richness and diversity index declined as the nutria index increased, but species richness increased as the frequency of muskrats increased. Any differences in emergent plant community structure between the weir managed marsh and unmanaged marsh, at Marsh Island, are less than observed differences between naturally well-drained and poorly-drained marshes. The lack of management effect was attributed to the lack of substantial soil drainage, even in the unmanaged marsh.
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