Date of Award

8-2011

Document Type

Open Access Thesis

Degree Name

Master of Science (MS)

Department

Biology

First Advisor

John P. Ebersole

Second Advisor

Richard Kesseli

Third Advisor

Robert D. Stevenson

Abstract

Phragmites australis is a perennial wetland grass that is native to North America. However, salt marshes, estuaries, and other wetlands throughout the northeast USA and Canada have witnessed a dramatic range expansion and population increase of the introduced genetic variant Phragmites australis haplotype M (Saltonstall 2002), with loss of native vegetation through competitive exclusion. Within the dune system of Sandy Neck Barrier Beach, freshwater wetland swales form in low elevation areas, which harbor a diverse wetland plant community dominated by shrubs, and sedges -- and including some rare and endangered species. To conserve and protect these wetland plant associations, annual herbicide applications were initiated in 2002 in a control program targeting the expanding populations of Phragmites M in the interdunal swales. To determine whether herbicide applications have reduced Phragmites infestations, estimated density and abundance scores from 2002-2009 were analyzed using a linear mixed model regression. Phragmite presence/absence data from the same time period was analyzed through binary logistic regression to determine whether herbicide applications were eradicating Phragmites from swales. The number of herbicide applications has significantly reduced the number of Phragmites stems within invaded swales, but the plant persists in all but a few of the treated swales. Data from a vegetation survey of 28 swales in 2010 were analyzed through cluster and multidimensional scaling analysis to investigate whether the composition of the plant communities differs between Phragmites-invaded swales versus swales never invaded by Phragmites. The vegetation found in uninvaded swales is distinctly different than that found in invaded swales. Additionally, the analysis of the survey data was used to determine whether reducing Phragmites in treated swales produces a vegetational shift toward non-Phragmites community structure. The analysis does not show that swales with reduced Phragmites plants have had a redevelopment of swale vegetation, similar to that found in uninvaded swales. More time or more herbicide applications may be necessary before changes to the plant community become evident.

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