Ecology of Bird Island, North Carolina: An Uninhabited, Undeveloped Barrier Island

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Title: Ecology of Bird Island, North Carolina: An Uninhabited, Undeveloped Barrier Island
Author: Rosenfeld, Kristen Marie
Advisors: Thomas R. Wentworth, Committee Chair
Abstract: Barrier islands include some of the most endangered and fragmented ecosystems on the Atlantic coast, providing critical habitat for many species, including some that are threatened and endangered. As the vast majority of these islands have been developed for human usage study and protection of the few remaining undeveloped and undisturbed islands is critical. This study was undertaken in order to characterize the vascular plant communities on Bird Island, an uninhabited, undeveloped barrier island on the border of North and South Carolina, with the objectives of a thorough survey of flora, vegetation, and environment, classification of plant communities, and multivariate analysis of vegetation and environmental data. A floristic inventory of the island and its associated marshes was conducted during the growing season (May-November) of 2002 and 2003. One hundred four 100m² plots were inventoried for vegetation and environment using protocols developed by the Carolina Vegetation Survey. Plant communities were identified according to the National Vegetation Classification, the Classification of the Natural Communities of North Carolina, and the Carolina Vegetation Survey. Interpretation of vegetation patterns was based on multivariate analysis of vegetation and environmental data. Ninety-one vascular plant species in 35 families, including 4 exotic species, were distributed across 12 communities. Communities on Bird Island appear to be distinctive when compared to those described for other barrier islands in the region. Additionally, the vegetation survey on Bird Island revealed suitable habitat for the federally listed Seabeach amaranth (Amaranthus pumilus); an important dune-building annual of the North American Atlantic coast. Surveys of the late 1980s and early 1990s documented small populations of Seabeach amaranth on Bird Island, but our work found no indication of a population in either 2002 or 2003. Seabeach amaranth's existence range-wide is threatened by habitat loss and fragmentation, herbivory, and anthropogenic disturbances such as beach driving, hardening, and raking. Published work on this species has been limited, but observations of natural, experimental, and restored populations have indicated relationships between distance from the ocean and both survivorship and reproduction. To quantify this relationship, 314 plants were transplanted at varying distances from the ocean. Plants were monitored monthly from June until December 2003. We found that distance from the ocean had a significant effect on survivorship, size, and reproduction; however, presence of webworms and ghost crabs did not have significant effects on size or reproduction. Distance from the ocean combined with complex factors such as over wash and soil salinity appear to be important indicators of success for both natural and restored populations of this species, and landscape position should be incorporated into future conservation and restoration efforts for A. pumilus in the Carolinas and elsewhere. Overall, we found that the vegetation of Bird Island is mostly intact, with few exotic, invasive species present. Bird Island's protected status and limited presence of invasive species make it suitable habitat for continued protection and further restoration of rare, threatened, or endangered species, such as Seabeach amaranth. Atlantic barrier islands in general provide distinct community types combined with a small species pool, a combination that may provide a model for examination of larger ecological questions.
Date: 2004-10-17
Degree: MS
Discipline: Botany

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