Date of Award

Winter 1996

Project Type

Dissertation

Program or Major

Plant Science

Degree Name

Doctor of Philosophy

First Advisor

Thomas D Lee

Abstract

Many wetland plant species can be found growing on Carex stricta Lam. (tussock sedge) tussocks in freshwater marshes. Based on Grime's model of plant species richness, the objectives of this research were to: (1) examine if dispersal characteristics vary among C. stricta marshes in a manner that could potentially influence species richness on individual tussocks, and (2) examine how variation in propagule availability may interact with standing crop and leaf litter to regulate species richness on individual tussocks. All of the research was conducted in southeastern New Hampshire.

Dispersal characteristics were quantified in five wetlands representing a broad range of average species richness per tussock. In each wetland, I observed patterns of plant colonization on 50 artificial tussocks (10 per site) over a one year period. In wetlands with high numbers of species per C. stricta tussock, species arrived at artificial tussocks at higher rates than at sites with few species per C. stricta tussock. Therefore, it was possible that variation in dispersal characteristics among wetlands could contribute to the observed differences in average species richness per C. stricta tussock. In addition, I found that the variation among wetlands in the rates at which species anived at artificial tussocks was due primarily to variation in numbers of dispersing species (species pool) rather than to variation in the densities of dispersing propagules per species.

In order to examine how variation in propagule availabilities may interact with standing crop and leaf litter to regulate species richness on C. stricta tussocks, I experimentally manipulated these factors using a factorial design involving 168 tussocks in three wetlands. Clipping of live C. stricta, removal of leaf litter, and addition of seeds from tussock inhabiting species all increased species richness on tussocks. Moreover, the magnitude of the limitation imposed by each was strongly dependent on the levels of each of the other factors. All of these relationships were consistent with Grime's model.

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