Aqropyron sm1 thi i/Bouteloua gracilis Community Type (Agsm/Bogr c.t. ). 

 The Agsm/Bogr c.t., a major community type in the study area, usually oc- 

 cupies low to mid slope positions. Coupland (1961) identified a Bouteloua- - 

 Agropyron faciation suggested the impermeable subsoils associated with this 

 faciation are unsuited to Stipa dominance. 



Hanson and Whitman (1938) identified a western wheatgrass-grama-sedge 

 type which typically contains more Carex than the Agsm/Bogr c.t. The 

 authors noted heavier soils in their wheatgrass-grama-sedge type than in 

 their grama-needlegrass-sedge type. They suggest that the western wheat- 

 grass-grama-sedge type is successional to the grama-needlegrass-sedge type 

 and is especially sensitive to drought. 



It is often said that an A. smi thi i is found on heavier soils than 

 Stipa comata . As a generalization this may be true; however, there is a 

 good deal of overlap in this respect, and it may be that generalizations 

 oversimplify the complex interactions involved. Morris (1976) has indicated 

 that soil color and texture, precipitation, and grazing should be taken into 

 account in summarizing the relative order of plant dominance. The existence 

 of ecotypes might make interpretations even more difficult. 



Stipa comata/Bouteloua gracilis-Carex filifolia Community Type (Step/ 

 Bogr-Cafi c.t. ). The Stco/Bogr-Caf i c.t. and the Bogr-Cari/Stco c.t. are 

 the most abundant types in the study area as reflected by the number of 

 reconnaissance samples falling into these categories. It is similar to the 

 grama-needlegrass-sedge type of Hanson and Whitman (1938), which they con- 

 sider to be the stabilized type on uplands given the climatic fluctuation 

 of the area. Coupland (1961) identified a Stipa - Bouteloua faciation and 

 noted that perhaps Carex should be added to the name. Coupland' s (1950) 

 Stipa-Bouteloua faciation appears to be similar to, but moister than this 

 type, as evidenced by the abundance of S^. spartea and A. das ytachyum in 

 his faciation. He suggests it is post climax to his Bouteloua-Stipa 

 faciation. 



Wright and Wright (1948) recognize a B. gracilis- S. comata type with 

 larger amounts of C. fil i folia on the sandier sites. Mueggler and Hand! 

 (1974) identified a S. comata/ B. gracilis habitat type for western Montana. 

 Smoliak et al. (19767 identified a Stipa - Bouteloua type associated with 

 medium textured soils in the drier Brown zone, coarser soils of the Dark 

 Brown zone and on sandy loam solonetzic soils. In our study area, the 

 Stco/Bogr-Cafi c.t. occurs mainly on loams and on mid to upper slope posi- 

 tions. 



Coryphantha vivipara exhibited fidelity for the S^. comata dominated 

 community types. (Fidelity was rarely observed for any species in this study). 

 Agropyron dasytachyum was sometimes present in the Stco/Bogr-Cafi c.t. 



Boutelcua gracilis-Carex filifol ia/Stipa comata Community Tvpe (Bogr- 

 Cafi/Stco c.t. ). The Bogr-Cafi/Stco c. t. is distinguished by a greater 

 coverage of B^. gracilis and C. filifolia than S^. comata . This shift in 

 dominance is probably the result of grazing (Smoliak 1965, 1974, Smoliak 

 et al. 1976), although S^. comata can persist under heavy grazing (Peter- 

 son 1962) through selection of grazing resistent ecotypes. This may not be 

 true in all habitats, however. 



27 



