t> 



5 



northwest-facing slopes above the gulch at 1890 m (T5S RlOW S14). 

 At Divide, 18 km east and 240 m lower, mean temperatures are 

 17.4° and -7.2° C for July and January respectively, and mean 

 annual precipitation is 31 cm. Vegetation is juniper woodland 

 dominated by Juniperus scopulorum , Cercocarpus ledifolius and 

 Agropyron spicatum . Effects of livestock grazing at this site 

 are minimal. At all three sites A^ fecunda occurs in soil with a 

 relatively high cover of cryptogamic soil crust. 



Methods 



We estimated percent cover of soil crust, bare soil, rock 

 and basal vegetation in transects using a point-frequency frame 

 (Mueller-Dombois and Ellenberg 1974, p. 86). Each transect 

 consisted of 12 1-m^ plots with 20 pins per plot for a total of 

 240 sample points per transect. The diameter of each pin was 2 

 mm, approximately equal to the diameter of an A^ fecunda taproot. 

 Since few plants occurred on rock or amongst the base of other 

 plants, we removed these points from subsequent analyses. We did 

 not observe any correlation between the spacing of crust patches 

 and that of the frequency pins. 



For each A^ fecunda plant in the plots we recorded whether 

 it was rooted in bare soil or soil crust. Since A^ fecunda 

 plants at these sites had a median age of 2-3 years (Lesica and 



