11 



stage classes between treatment and control plots at either site 

 (Table 6). However, at Charley's Gulch, there was a trend for 

 plants in both S, and R, classes to become larger in the 

 treatment plots. Lack of a significant difference is probably 

 due to the small sample size. If these two classes are combined, 

 the difference between treatment and control is significant 

 (X 2 =3.957, p<0.05) . 



At both Birch Creek and Charley's Gulch, the equilibrium 

 growth rate (lambda) of Arabis fecunda for the first two years of 

 the study was significantly larger in plots with Centaurea 

 maculosa removed compared to controls (Table 7) . At Birch Creek 

 the equilibrium growth rate is larger for the first three years 

 as well, but the difference is not significant (Table 7). Over 

 the study period, equilibrium growth rates of Aj_ fecunda in 

 control plots were not significantly different from 1.0 (p<0.05). 



Discussion 



The results of our study indicate that Centaurea maculosa is 

 competing with Arabis fecunda and that this competition is being 

 effected primarily by a reduction in recruitment (preemptive 

 competition sensu Werner 1979) rather than interference at later 

 stages. During the first two years following removal of C^. 

 maculosa , both equilibrium qrowth rate calculated from projection 

 matrices and simple qrowth rate of At fecunda populations were 



