While grazing may cause the reversal of dominants in this and other 

 community types, weather may also be a strong determinant (Houston and 

 Woodward, 1966). Reed and Peterson (1961) observed that major weather 

 cycles set major trends in mixed prairie vegetation characteristics, while 

 grazing intensity determines the rate of change within trends. Coupland 

 (1950) associated his Bouteloua - Stipa faciation with drier sites than the 

 Stipa-Bouteloua faciation. 



Poa sandberqii was more abundant in the Bogr/Agsm, Bogr-Cafi/Stco, 

 and Bogr-Cafi/Agsm-Stco c.t.'s than in the Agsm/Bogr, Stco/Bogr-Caf i , and 

 Stco-Agsm/Bogr c.t.'s. 



Stipa comata-Aqropyron smithii/Bouteloua gracilis Community Type (Stco - 

 Agsm/Bogr c.t. ) In the Stco-Agsm/Bogr c.t. the two midgrasses share dom- 

 inance, with S^. comata usually having the higher coverage. The Stco-Agsm/ 

 Bogr c.t. perhaps represents an area of gradation between the Stco/Bogr- 

 Cafi and Agsm/Bogr c.t.'s. If so, the Stco/Agsm/Bogr c.t. is a fairly con- 

 stant and recognizable area of gradation. 



Coupland (1961) recognized a Stipa-Bouteloua-Agropyron faciation, and 

 Smoliak et al. (1976) identified a Stipa-Agropyron type. Morris (1976) re- 

 cognized the unequally shared dominance of S. comata a nd A. smithii on both 

 sandy and clay loams under moderate grazing. The Stco - Agsm/Bogr c.t. may 

 also be related to the A. smithii - A. d asytachyum phase of the S. comata/ B. 

 gi^acilis habitat type of Mueggler and Handl (1974). 



Bouteloua qracilis-Carex filifolia/Agropyron smithii-Stipa comata Com- 

 munity Type (Boqr-Cafi/Aqsm-Stco c.t. ). The Bogr-Cafi/Agsm-Stco c.t. is 

 identified by a greater coverage of B. gracilis and C. filifolia than A. 

 S"iithii and S^. comata , and occupies warmer sites than sites for the Stco- 

 Agsm/Bogr c.t. This type juay represent a heavily grazed phase of the Stco- 

 Agsm/Bogr c.t. Stipa- Carex-Agropyron dominated climax stands became dom- 

 inated by Carex and Bouteloua under grazing (Coupland et al . 1960). 



The simultaneous increase in abundance of C. filifolia and reversal 

 of dominance between S^. comata and A. smithii raises a problem in inter- 

 pretation if A. smithii is taken to be suggestive of heavy soils and C. 

 filifolia of light soils. The western wheatgrass-grama-sedge type of 

 Hanson and Whitman (1938) may indicate that the association of C. filifolia 

 and A. smithii is not unusual, but Morris (1971) associated the species with 

 different soils. 



Stipa viridula - Agropyron smithii/Bouteloua gracilis Community Type 

 (Stvi-Aqsm/Bogr c.t.) . The Stvi-Aqsm/Boqr c.t. is generallv found in areas 

 with above average moisture and heavier than average soils. A depression of 

 soil carbonate levels might also be associated with S^. virdula . It is not 

 restricted to vertisols in the study area. This type is often found in 

 swales and coulees. Morris (1971) associated communities of i. virtlula , A. 

 smithii . and variable amounts of B^. gracilis , with moderately developed soils 

 on benches and near level plateaus in southeastern Montana. Echinacea pallida 

 and Ratibida col un if era , usually associated with moister than average sites, 

 are sometimes present in the Stvi -Agsm/Bogr c.t. 



28 



