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The Louisiana coastal marshes form some of the most extensive wetlands within the continental United States. The problem of land loss in these coastal marshes is well-documented, but very little is known about possible changes in vegetation composition that might be associated with this loss. We analyzed vegetation data collected from 1968 to 1992 in the tidal wetlands of Terrebonne parish and described five vegetation types that occur in this region. Our data did not show the predicted change to more salt-tolerant vegetation. This is probably due to the influence of the Atchafalaya River in the study area. However, we documented a large change in the dominant vegetation of the fresh marsh. Panicum hemitornon-dominated marshes occupied 51% of the study area in 1968 and only 14% in 1992. This vegetation type was replaced with Eleocharis baldwinii-domJnated marshes (3% in 1968 to 41% in 1992). This change occurred adjacent to an area of significant conversion to open water. Based on limited available data from the literature, we ev',duated three potential driving factors in this change-grazing, water-level increase, and water quality-but could not determine the cause of change definitively.

Nutria (Myocastor coypus) diets and food preferences in selected freshwater forested wetlands of Louisiana were determined by microhistological examination of fecal pellets and stomach contents. Lemna minor and Spirodela polyrrhiza (duckweeds) dominated the diet (yearly mean 55.5%) during all seasons on 4 of 6 sites sampled. Nutria also ate substantial amounts of Pontederiaceae (Eichhornia crassipes and Pontederia cordata) (9.9%), Alternanthera philoxeroides (8.3%), Poaceae (mostly Panicum gymnocarpon) (5.1%), and woody tissue (6.8%). Nutria diets varied among seasons, with spring diets containing more Poaceae (P<0.01) and less Pontederiaceae (P<0.01) than during other seasons. Nutria showed seasonal preference for L. minor and S. potyrrhiza (spring and summer), Po aceae (spring), A. philoxeroides (summer and winter), and Cyperaceae (summer and fall). SinceL. minor and S. polyrrhiza dominated nutria diets even when they had relative cover values as low as 16.8%, nutria habitat quality should improve if freshwater forested wetland understories are converted (throughnatural or anthropogenic forces) to communities dominated by these plant species.

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