Effect of the invasive exotic herb Centaurea solstitialis on plant communities of a semiarid ecosystem.
Background The effects of many invasive species on invaded communities are still scarcely known. Centaurea solstitialis is an invasive Eurasian herb, widely distributed around the world, but its effects on recipient communities are not well known. Aims To evaluate the effect of C. solstitialis invasion on richness and cover of native and exotic resident species in naturally established communities. Methods We repeated a field experiment in three old-fields of central Chile where C. solstitialis was not present. The experiment simulated the invasion of C. solstitialis by adding 600 seeds per plots of 1 × 1 m in size and compared the richness and cover of all naturally growing species in plots with and without C. solstitialis. Results For exotics, initial species richness (average ca.18% and 20% per site), and cover (average ca. 20% and 34% per site) were significantly reduced by C. solstitialis in two out of the three sites. The abundances of four out of 17 exotic resident species were negatively affected by C. solstitialis. Native species were not affected by C. solstitialis. Conclusions C. solstitialis can outcompete resident species of communities where it invades, but local ecological factors influence its effects producing different impacts among species and localities.