Does Woody Species Establishment Alter Herbaceous Community Composition of Freshwater Floating Marshes?

Abstract

Abstract Floating freshwater marsh communities (flotant) in the Mississippi Deltaic Plain are composed of vegetation rooted in an organic mat that detaches from the underlying mineral substrate and shifts vertically as water levels below rise and drop. Unlike attached marshes dominated by herbaceous species, floating marsh mats are free from the stress of inundation, enabling establishment of woody species. Dynamics of these flotant communities are largely unstudied, and it is unknown whether invasion by woody species alters their structure and composition. To study the potential effects of woody species invasion on herbaceous community characteristics, we compared open herbaceous marsh, sparse scrub-shrub, and dense scrub-shrub thickets at Jean Lafitte National Historical Park and Preserve in coastal Louisiana. We found that species richness and composition differed significantly among the three marsh types. Herbaceous communities lacking shrub canopies had the lowest richness and were dominated by emerg...