Effects of herbicide on the invasive biennial Alliaria petiolata (garlic mustard) and initial responses of native plants in a southwestern Ohio forest

Restoration often includes control of invasive plants, but little is known about how native plant communities respond to this control. The biennial Alliaria petiolata (M. Bieb.) Cavara and Grande (garlic mustard) is one of the most prevalent invasive plants in forests of eastern North America. We investigated the effects of the herbicide Round-up (glyphosate) on Alliaria and the response of the forest floor plant community to the herbicide and the subsequent decline of Alliaria. In an old-growth Acer-Fagus stand and a second-growth Liriodendron-dominated stand in Hueston Woods State Nature Preserve, Ohio, United States, we spot applied Round-up in November 2000 and 2001 in 25 1x1-m plots and maintained 25 control plots. Herbicide decreased Alliaria density in both stands and reduced the density of other species in leaf during treatment (mostly exotic winter annuals) in the old-growth stand. Treatment did not affect the initial density of the Alliaria cohort that germinated in the spring of 2001, but decreased the 2002 cohort. Community differences were found in the old-growth stand after Alliaria reduction, specifically greater cover of spring ephemerals in the herbicide treatment. In the second-growth stand, herbicide treatment increased reproduction of the late-summer perennial, Phryma leptostachya. These results indicate that glyphosate reduces Alliaria without negatively impacting native species and that some native species respond positively to a single-year reduction in this invasive biennial.