Faculty Scholarly Dissemination Grants


Native plant establishment influenced by the method used to control spotted knapweed


Biology Department


College of Liberal Arts and Sciences

Date Range



Life Sciences


Restoring native plant communities on disturbed sites is hampered by invasive species, including spotted knapweed. Our objective was to determine effective treatment combinations to increase native plant establishment while controlling knapweed on a degraded site in western Michigan. We applied a factorial combination of treatments to 48 5-m by 5-m plots. Site preparation treatments utilized in 2008 included mowing, alone and in combination with single applications of clopyralid or glyphosate. We seeded all plots in May 2009 with native grasses and forbs representative of Michigan dry prairies. Additional treatments included annual hand pulling of bolted knapweed, commencing in July 2009, and a prescribed burn in April 2012. In July 2011 and 2012, we estimated percent cover of all species on each plot and calculated relative percent cover, mean coefficient of conservatism (mean C), and the floristic quality index. By 2011, seeded native grasses and forbs had established on all treatment combinations, even on mowed-only plots with >50% knapweed cover. Glyphosate favored the establishment of some native species, but allowed rapid reinfestation by knapweed. Clopyralid maintained reduced knapweed cover, shifted plant communities toward non-native grasses, and resulted in greater mean C in both 2011 and 2012. In comparison, hand pulling maintained low knapweed cover (<0.1%) regardless of site preparation treatment and produced increased cover of several native forbs and grasses. In contrast, burning had little effect on plant community composition. Our results showed that knapweed control methods played a large part in determining the trajectories of the developing native plant communities.

Conference Name

SER2013 World Conference

Conference Location

Madison, WI

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