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diameter, occur at the study sites interspersed in a matrix of 

 bare mineral soil and rock. 



During the course of a demographic monitoring study at three 

 sites, we noticed that A^ fecunda appeared to be 

 disproportionately common in soil crust compared to bare soil. 

 At two of the sites the crusts had been disrupted by livestock. 

 The purpose of our study was to document any association between 

 A. fecunda and the occurrence of soil crust and to begin to learn 

 the causes of this association. 



The Study Areas 



We conducted our study at Birch Creek and Charley's Gulch in 

 Ravalli County and at Lime Gulch in Beaverhead County. The Birch 

 Creek site is on a steep, eroding, southeast-facing slope at 14 3 

 m (T7N R19W S16) . The Charley's Gulch site is on an eroding, 

 southwest-facing slope at 1525 m (T6N R19W S19) . At Hamilton, 

 ca. 8 km southwest and 300 m lower, mean temperatures for July 

 and January are 19.9° and -4.4° C respectively, and mean annual 

 precipitation is 32 cm. Zonal vegetation surrounding the Ravalli 

 County sites is foothills Aqropyron - Festuca grasslands (Weaver 

 1980) with scattered Pinus ponderosa and Pseudotsuga menziesii . 

 The effects of trampling and grazing by livestock are noticeable 

 at both sites. The Lime Gulch site is on southeast and 



