11 



Although Arab is fecunda is locally abundant, it occurs in 

 only two relatively small and widely separate areas, and fewer 

 than fifteen populations have been discovered. All of the 

 Ravalli County populations are subjected to heavy grazing 

 pressure from livestock. Trampling by livestock has been shown 

 to destroy cryptogamic soil crusts in the shrub-steppe of 

 southern Utah and northern Arizona (Brotherson et al. 1983, 

 Johansen and St. Clair 1986) , and we have observed destruction of 

 soil crusts by cattle during the course of our long-term 

 monitoring at the study sites. Soil crusts are slow to recover 

 after disturbance; Johansen and St. Clair (1986) found that 

 crusts in Utah had not fully recovered from the effects of 

 livestock trampling after seven years, and Anderson et al. (1982b) 

 estimated that recovery takes 14-20 years. Although livestock 

 probably do not graze A^ fecunda , they have a negative impact on 

 some Aj. fecunda populations by trampling plants and destroying 

 the beneficial soil crusts on steep slopes where mass soil 

 slumping is easily induced. Over the long-term, trampling of its 

 steep erodible habitat could lower A^ fecunda density, thereby 

 decreasing population viability of this rare species. 



