Submitted to: Plant Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/10/2010
Publication Date: 4/12/2011
Citation: Reinhart, K.O., Rinella, M.J. 2011. Comparing susceptibility of eastern and western U.S. grasslands to competition and allelopathy from spotted knapweed (Centaurea stoebe L. subsp. micranthos (Gugler) Hayek). Plant Ecology. 212:821-828.
Interpretive Summary: • Field measures and a greenhouse experiment were performed to address whether a species that is highly invasive in some regions behaves in an entirely new region. This study focused on spotted knapweed which is a highly aggressive invasive plant in the western U.S. This study suggests spotted knapweed may not be an aggressive invader in an eastern grassy bald. • Field measures indicate that increasing densities of knapweed did not correspond with reductions in native species. The greenhouse experiment revealed that spotted knapweed was much more negatively affected by three plant species from the eastern grassy bald than the two grasses from invaded communities in the western U.S. This suggests the grassy bald community is relatively resistant to invasion by spotted knapweed. • Spotted knapweed has a reputation for using allelopathy (chemical root exudates) to negatively affect resident plants, however, the population of knapweed from the grassy bald had no measurable allelopathic effects on any of the tested plant species. • Management implications- It appears that in some communities, spotted knapweed does not behave as an aggressive weed and may not warrant aggressive control measures (e.g. broadcast herbicide spraying) which may do more harm to the resident community than the invader.
Technical Abstract: Centaurea maculosa is native to Eurasia and is invasive in the western portion of the US. Negative impacts of C. maculosa present in the eastern US have not been recorded. In this study, we examine the effects of C. maculosa on species diversity on an eastern grassy bald, compare the competitive abilities of eastern and western plant species against C. maculosa, and assess the production of allelopathic compounds in an eastern population of C. maculosa. Field observations indicated that increasing C. maculosa abundance was not associated with decreasing abundance or diversity of species. In a greenhouse experiment, C. maculosa growing with eastern plant species was smaller than C. maculosa growing with western species, indicating that eastern species are more competitive against C. maculosa than western species. We did not find evidence that the eastern population of C. maculosa has allelopathic effects. Thus, the lack of weapons in the arsenal of eastern populations of C. maculosa combined with the competitive ability of eastern species indicates that C. maculosa may not become invasive in the eastern US. While these populations may simply be in the lag phase of invasion, the possibility that they may never become invasive should be weighed when considering C. maculosa control measures in the eastern US. This study illustrates that invasion dynamics can vary geographically and illustrates the need for this information by managers who must gauge an appropriate and economical response to a newly detected weed.