Competitive effects of Centaurea maculosa on the population dynamics of Arabis fecunda1

plots for two years at one site and four years at the other. We analyzed differences between treatment and control in recruitment, survival, individual growth and fecundity separately. Estimates of equilibrium population growth (X) were obtained from matrix projection models to evaluate the overall competitive effects of C. maculosa on A. fecunda. Over the course of the study X was significantly higher in treatment plots compared to controls, indicating that C. maculosa had a negative effect on A. fecunda populations. Recruitment was significantly higher in treatment plots during the first two years of the study. Survival, growth and fecundity did not differ between treatment and control. These results indicate that the main effect of removing C. maculosa on populations of A. fecunda was enhanced recruitment resulting from increased seedling establishment. Competitive effects of C. maculosa on A. fecunda varied between sites and among years, indicating that long-term studies are required to fully understand the effects of competition on population dynamics.