9 



equally in crust. At Birch Creek and Lime Gulch South, small 

 non-reproductive plants were fewer than expected in soil crust. 

 Since most plants in this life stage class are less than one year 

 old, it appears that seedling establishment and survival was 

 higher on bare soil. On the other hand, plants in the older, 

 reproductive life stage class were more common than expected in 

 soil crust. Results from these two transects suggest that 

 survival of Arabis fecunda after the first year was enhanced for 

 plants rooted in crust. Differential survival of older/larger 

 plants may partially explain the observed association between A. 

 fecunda and soil crust. 



Cryptogamic soil crusts decrease permeability to water 

 compared to bare soil (Loope and Gifford 1972, Brotherson and 

 Rushforth 1983) and may, under some circumstances, reduce 

 seedling establishment (St. Clair et al. 1984). Although St. 

 Clair et al. (1984) found that soil crust enhanced establishment 

 of two grasses in the greenhouse, Arabis fecunda has much smaller 

 seeds than most grasses, and germinating seeds of A^ fecunda may 

 not possess the resources required to easily penetrate the crust. 



Crusts increase soil fertility by adding to the organic 

 matter (Fuller and Rogers 1952) and through nitrogen fixation 

 (Snyder and Wullstein 1973, Rychert and Sku j ins 1974). The 

 presence of crust is also correlated with deeper water 

 penetration, probably due to the associated microtopographic 



