296 THE STUDY OF PLANT COMMUNITIES * Chapter X 



western Oklahoma into Texas. The sand hills of Nebraska are an 

 exception, for here soil conditions are such that postclimax tall 

 grasses predominate. During protracted dry periods, the short 

 grasses increase at the expense of the moisture-requiring tall 

 grasses. 267 Thus the boundaries of the association are not particu- 

 larly static and are represented by a wide transition zone. 



FlG. 159. Short grass range in Colorado under average grazing and con- 

 sequently in good condition.— U. S. Forest Service. 



Short Grass Plains— Westward from the Mixed Grass Prairie to 

 the woodland zone of the Rockies, the xeric short grasses are dom- 

 inant. On the basis of exclosure studies and other observations, the 

 climax nature of short grasses has been questioned, and the com- 

 munity has been described as disclimax resulting from overgrazing 

 an area that would otherwise support mixed prairie. 268 This inter- 

 pretation is gradually gaining favor. Regardless of terminology, 

 the short grasses are, at present, dominant over the entire area. 



The most important species are Bouteloua gracilis and Balbilis 



