Alliaria petiolata: Impact on native spring ephemerals and successful control in a maple beech forest

Background/Question/Methods

Invasive species remain a major cause of global species extinction. In southeastern Wisconsin. Alliaria petiolata has invaded the spring ephemeral understory of a large maple beech forest remnant for the past two decades. A. petiolata is an obligate biennial with a phenology typical of cool-season plants that end dormancy early in the season. This species is allelopathic and shade-tolerant allowing it to compete with native species. We compared native spring ephemeral diversity in plots containing garlic mustard with non-invaded plots. At the end of the census, we removed garlic mustard from the plots.  Eradication efforts were limited to mechanical removal in study plots and in surrounding patches, mostly near the tributary or near the base of trees.

Results/Conclusions

Although species richness was equal between plots, species composition differed. Early ephemerals that were spatially displaced included Erythronium albidum, Geranium maculatum, Dentaria laciniata, Claytonia virginica, Geum canadense, Trillium grandiflorum, Hepatica americana, Smilacina racemosa, and Asarum canadense, as well as certain tree species. For example, lower populations of Fagus grandifolia and higher populations of Acer saccharaum were found in invaded patches. After two seasons of intense plant removal, the invaded plots showed signs of composition shift. In the third season, we found very few first year plants, even near previous dead stalks that had not been removed. This study offers preliminary optimism for non-destructive eradication and restoration in old-growth forests. Other current work in this study include investigating potential causes of invasiveness such as seed resistance to a fungal pathogen or shifts in soil microbial diversity.