Submitted to: AoB Plants
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/11/2015
Publication Date: 6/2/2015
Citation: Rauschert, E., Shea, K., Goslee, S.C. 2015. Plant community associations of the invasive thistles. AoB Plants. doi: 10.1093/aobpla/plv065. Interpretive Summary: The invasive thistles Carduus nutans and C. acanthoides are an economic problem in pastures of the northeastern United States. Field sampling was carried out at four sites to identify differences in plant community composition and in species abundances that were related to the presence and absence of thistles. There were no differences in composition between plots containing either of the two thistles, but certain species were regularly associated with the presence or absence of thistles. Notable, white clover was more abundant in plots without thistles. Invasion by thistle can have broader impacts on plant communities than simply increasing the cover of thistle without altering the proportions of other species.
Technical Abstract: In order to combat the growing problems associated with biological invasions, many researchers have focused on identifying which communities are most vulnerable to invasion by exotic species. Once established, invasive species can significantly change the composition of the communities that they invade. Carduus nutans and C. acanthoides are similar invasive thistles, which have caused considerable economic damage worldwide. As a first step in understanding the factors that mediate the abundance of these two species, we assessed their associations with the standing flora in four sites in central Pennsylvania in which they co-occur by sampling nearly 2000 one m2 plots. We found significant differences in community composition in plots with and without Carduus thistles. Sisymbrium officinale and Coronilla varia were consistently associated with the presence of Carduus thistles. Several species were associated with areas that were free of Carduus thistles, including an important pasture species (Trifolium repens). We found no evidence for differences in composition between plots with C. nutans versus C. acanthoides, suggesting that they have similar associations with the vegetation community. We conclude that even at the within-field scale, areas invaded by Carduus thistles have different vegetation associations than uninvaded areas, raising questions about the role of vegetation structure in resisting and responding to invasion.