A biogeographical comparison of the invasion success of Centaurea solstitialis between California and central Argentina

HIERRO, J.L., D. VILLARREAL, AND R.M. CALLAWAY

Portland, Oregon, Estados Unidos

Congreso; Ecological Society of America Annual Conference; 2004

Centaurea solstitialis, an annual herb native to Eurasia, has been introduced to grasslands worldwide, but it varies in invasion success. Preliminary observations suggest that the abundance of this weed is much greater in California than central Argentina. As part of a series of parallel experiments assessing the role of local climates, resident vegetation, and invader genotypes in this biogeographical pattern, we conducted a field experiment evaluating the invasion success of C. solstitialis and the importance of disturbance in this success in California and central Argentina. In each region, we added a known number of locally collected C. solstitialis achenes into plots with the following treatments: soil turnover, burning, clipping, and no disturbance. As expected, levels of invasion, determined by plant density and percent cover, in both regions were significantly higher in disturbed than undisturbed plots, but the response of C. solstitialis to disturbance differed between regions. While in California soil turnover and burning plots resulted similarly invaded and both treatments showed higher levels of invasion than clipped plots, in central Argentina soil turnover plots were more invaded than any other treatment and there were no differences between burned and clipped plots. Soil turnover and burning resulted significantly more invaded in California than central Argentina. In contrast, invasion was higher in non-disturbed plots in central Argentina than those in California. Levels of invasion were similar for the clipping treatment in both regions. Results suggest that differences between regions in the response of the local plant community to disturbances can greatly contribute to observed variations in the invasion success of this species, and highlight the context-dependent nature of several biological invasions.