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theses

Wetlands provide crucial ecosystem functions that aid water security, stormwater management, and biodiversity conservation. However, the underlying mechanisms that influence headwater wetlands in urban landscapes are poorly understood. Further, biodiversity loss may reduce ecosystem function and increase the transmission risk for some enzootic diseases, such as West Nile virus (WNV). My research aimed to: 1) assess wetland vegetation structure and the importance of fragment size and landscape position on biodiversity; 2) test the importance of flooding conditions for mitigating invasive plant dominance in forested wetlands using Japanese stiltgrass (Microstegium vimineum) as my study system; and 3) identify relationships between vegetation structure, fragment size, and the relative abundance of competent avian WNV hosts and mosquito vectors. I used a combination of measurative and experimental research methods to address these objectives, the third of which was part of a collaborative interdisciplinary research grant. Vegetation structure was measured in 36 plots located in six forested wetlands and data loggers were used to monitor aboveground flooding. Avian and mosquito research teams coordinated iii with my sampling points. My results illustrate the capacity for urban headwater wetlands to support a diverse flora, as well as the complex interactions between human activities and wetland structure and function. Red maple, oak, sweetgum, and green ash were the dominant tree species. Half of the 287 plant species identified only occurred at 1-2 sample points. Groundcover composition reflected the confluence of hydrogeomorphology, and past and present human actions. Connectivity via nearby streams or ditches had a greater impact on exotic plant richness than did wetland patch size. Aboveground flooding prior to seedling emergence significantly reduced the distribution of Japanese stiltgrass. Avian species richness was positively correlated with plant richness. In contrast, mosquito richness was negatively correlated to plant richness. WNV hosts and vector abundance both increased with maple (Acer spp.) tree canopy dominance. Cumulative host abundance averaged 24% and was composed primarily of American Robin, which showed large interannual shifts in fragments <15 ha. The relative abundance of competent vectors ranged from 5 to 26% and their populations demonstrated less interannual variation than were observed in the host populations.

ETD_6853

Ph.D.

Includes bibliographical references

by Laura Jean Shappell

doi:10.7282/T37W6F54

ETD doctoral

The author owns the copyright to this work.