Understanding Plant Community Composition In Agricultural Welands: Context Dependent Effects And Plant Interactions

Community composition results from an integrated combination of random processes, regional habitat spatial structure, local environmental conditions, and species interactions. For example, the outcome of plant interactions can change depending on local environmental conditions such as nutrient availability, land management, or herbivory intensity. In particular, plant interactions may vary between facilitation and competition depending on ecological context, with facilitation expected to be prevalent under stressful conditions. I present the results of four studies that address different aspects of the community assemblage and dynamics emphasizing the synergistic effect of different processes. In the first, I investigated the importance of habitat isolation in determining species richness of wetlands with contrasting land use. The second describes an experiment to test the hypothesis that plant interactions with an unpalatable plant (Juncus effusus) would range from competition in ungrazed areas to facilitation in grazed areas and predicted that facilitative effects of Juncus would differ among functional groups of beneficiary species and be strongest when grazing was intense. In the third, I examine the community composition impacts of Juncus and predicted that Juncus would preserve functional diversity in grazed wetlands but that the effects of Juncus would vary along a grazing gradient. The fourth study investigated the relative importance of competition and nutrients in determining wetland invasion in two different land use types. Broadly, I demonstrate that the importance of different processes (habitat isolation, nutrient availability, competition/facilitation) to community composition is dependent on ecological conditions. This integrated view of community dynamics is interesting from a purely ecological perspective but also can be applied to understanding ecological problems such as exotic invasions and restoration of disturbed habitats