Degree Name

Master of Science (MS)

Semester of Degree Completion

Spring 2019

Thesis Director

Scott J. Meiners

Thesis Committee Member

Yordan S. Yordanov

Thesis Committee Member

Robert E. Colombo

Abstract

Although plant invasions are of major conservation concern, understanding of the natural controls on invasion and their impacts is largely limited to static observational studies or artificially manipulated systems. Linking patterns of invasion with subsequent impacts in natural systems is necessary to fully assess invasion causes and consequences. Therefore, I employed a long-term approach to sequentially assess the controls on invasion and their subsequent impacts in a self-assembled system for the highly invasive annual grass Microstegium vimineum. I modeled likely factors contributing to the probability of invasion and local invasion success of a natural invasion of M. vimineum in a forest understory between two time windows of 2001/2002 and 2007/2008. Following invasion, I also followed plots to determine the impacts of M. vimineum invasion. The probability of invasion was positively associated with herbaceous species richness and negatively associated with distance from the nearest invaded plot (a measure of propagule pressure). Following invasion, the increase in cover of M. vimineum in each plot was positively related to herbaceous plant cover and negatively related to both distance to the nearest invaded plot and tree cover. Invaded plots lost significantly more herbaceous species richness and cover at high levels of invasion relative to lightly or uninvaded plots. Problematically, the observed impacts on richness and herbaceous cover were dependent on their patterns of initial invasion success. These results suggest controllers of invasion can confound impact assessments, in this case offsetting each other.

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