Date Approved

12-2013

Graduate Degree Type

Thesis

Degree Name

Biology (M.S.)

Degree Program

Biology

First Advisor

Neil W. MacDonald

Second Advisor

Todd A. Aschenbach

Third Advisor

Timothy M. Evans

Abstract

Invasive species frequently hinder restoration efforts. While the effectiveness of differing control methods are often reported, the impacts these methods have on the establishment of a native plant community are often unknown. To determine methods that effectively reduce spotted knapweed (Centaurea stoebe) while enhancing native species establishment, we tested 12 treatment combinations consisting of an initial site preparation (mowing, mowing + clopyralid, or mowing + glyphosate), with combinations of annual adult knapweed hand pulling, and/or burning. We established 48 plots and applied site preparation treatments during summer 2008, seeded 23 native forbs and grasses during spring 2009, pulled adult knapweed annually from 2009-2012, and burned in the early spring 2012. During July of 2011 and 2012, percent cover of all species was visually estimated. By 2011, seeded species had established in all treatment plots, including plots that retained greater than 50% knapweed cover, indicating that native species successfully established despite knapweed dominance. Mowing alone had no long-term impacts on community development. Clopyralid favored non-native grass establishment, while glyphosate encouraged non-native forbs. Clopyralid had minimal impacts on native forb establishment, but did effectively control knapweed. Hand pulling reduced knapweed cover, increased non-native grass cover, and enhanced native species establishment. The established grasses helped prevent the resurgence of knapweed. Further, native graminoids were beginning to replace non-native grasses in the pulled plots. Burning had little impact, possibly due to low intensity and unseasonable weather. The application of knapweed control measures combined with seeding of native species resulted in successful native species establishment.

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