10 



patterning (Loope and Gifford 1972, Brotherson and Rushforth 

 1983) . In addition, soils covered with crust retain moisture for 

 longer periods of time (Booth 1941) . The improved water and 

 nutrient relations associated with crust should be beneficial to 

 plants once they have penetrated the crust and become 

 established. The observed increase in survivorship of 

 older/larger plants at Birch Creek and Lime Gulch South supports 

 this hypothesis. 



In spite of the fact that older/larger plants appeared to be 

 favored on soil crust in two of the transects, the three measured 

 components of fecundity were not enhanced on crust. Furthermore, 

 although there were more reproductive plants than expected on 

 soil crust at Birch Creek, there was no evidence for increased 

 individual fecundity. In fact, there was a tendency for measures 

 of fecundity to be higher for plants in bare soil. 

 These results suggest that survivorship and fecundity are not 

 tightly linked in A^ fecunda . 



Our study has shown that Arabis fecunda occurs more commonly 

 in soil crust than would be expected by chance. This association 

 may occasionally be due to increased seedling establishment but 

 is more likely due to enhanced survivorship of older plants. It 

 seems clear that some populations of A^. fecunda benefit from the 

 presence of soil crust. 



