t 



2 



retention (Booth 1941) . Nonetheless, there is debate on the 

 value of soil crusts in semi-arid grasslands, shrublands and 

 woodlands. Some rangeland ecologists believe that crusts seal 

 the soil surface, curtailing the establishment of vascular plant, 

 especially grass, seedlings (Savory and Parsons 1980, Savory 

 1988). On the other hand, Nebeker and St. Clair (1980) and St. 

 Clair et al. (1984) have shown that, under some circumstances, 

 seedling establishment can be enhanced in soil crusts. Different 

 types of crusts (i.e. pinnacled vs. flat) may have different 

 properties, and this may be the source of the apparent 

 contradictions in research results (J. Johansen, pers. comm. ; see 

 Brotherson and Rushforth 1983 for pictures of typical pinnacled 

 crusts) . Soil crusts are very sensitive to disturbance (Kleiner 

 and Harper 1977, Anderson et al. 1982a, Brotherson et al. 1983) 

 and recover slowly following disruption (Anderson et al. 1982b, 

 Johansen and St. Clair 1986) . 



Arabis f ecunda Rollins is a rosette-forming, short-lived 

 perennial in the Mustard Family (Brassicaceae) . This recently 

 described species (Rollins 1984) is endemic to highly calcareous 

 soils in the foothills of the Sapphire Range in Ravalli County 

 and in the Pioneer Range in Beaverhead and Silver Bow counties in 

 southwest Montana (Lesica 1985, Schassberger 1988) . Plants bloom 

 in early spring and disperse seed during early to mid-summer. 

 The small (ca. 1 mm) seeds germinate readily without 

 stratification (Lesica, unpublished data) . Presumably most 



