Title

Dynamics of the submerged plant community in a freshwater tidal marsh

Date of Completion

January 2003

Keywords

Biology, Botany|Biology, Ecology

Degree

Ph.D.

Abstract

A freshwater tidal marsh plant community is characterized, using ordination to explore what abiotic variables are most important in determining presence and abundance of species. I established permanent transects to determine the degree of change among submerged plants over a six-year period and compared community structure and dynamics among five freshwater tidal marshes. The five communities were found to be sufficiently similar to suggest that metapopulation models may be useful in thinking about these communities. However, abundance of species changes independently among the communities. A field experiment showed that wintertime sediment shifting is a previously unrecognized source of disturbance among submerged plants, and computer simulations found that sediment shifting can have a significant effect on species richness and variation at small spatial scales. The degree of the effect varies with patchiness. In such highly disturbed communities, colonization is essential to persistence, and I explored the relative importance of the seedbank and vegetative propagules by sampling the seedbank, sampling the vegetative propagule stream and observing recolonization in cleared plots. Finally, I used data on vegetative propagule abundance and autecology to develop predictions on species' colonization success and persistence, and I tested those predictions using data obtained in the permanent transect censuses, concluding that vegetative propagule abundance is largely responsible for colonization success and abundance of plants in the community, although a limit apparently exists beyond which production of additional propagules results in no additional colonization. The results also show that production of vegetative tubers deep in the sediment protects some species from disturbance, resulting in higher persistence levels. ^