CLIMAX COMMUNITIES : PRESENT DISTRIBUTION 297 



dactyloides, except north of the Dakotas, where the latter is ab- 

 sent. Several faciations are recognizable that result from combina- 

 tions of the major dominants with Stipa comata, or Agropyron 

 smithii, or Aristida longiseta. 



The desert plains area extending from western Texas across 

 northern Mexico and southern New Mexico and Arizona supports 

 short grasses, which, although including different species, are re- 

 lated to short grass dominance. Several species of Bonteloiia and 

 Aristida predominate. Overgrazing has greatly increased the num- 

 bers of desert shrubs here, and these include Larrea, Gpuntia, 

 Flourensia, and several others of which widely spaced individuals 

 occur everywhere. 



Other Grassland Climax— There is evidence that the great valley 

 of California was once dominated by grasses, which, because of 

 fire and grazing, have been eliminated except for relict areas. The 

 latter suggest that the dominants were bunch grasses, which pro- 

 duced grassland similar in appearance to mixed prairie. Through- 

 out most of the area it appears that Stipa pulchra was the principal 

 species, except near the coast. Today introduced annual grasses 

 occupy most of the remaining grassland areas, especially species 

 of Avena, Bromus, Festuca, and Hordeum. 



The rolling hills of the Palouse region, as well as most of eastern 

 Washington and Oregon and eastward into Idaho, supported 

 prairie grasses before being cultivated for wheat production. Al- 

 though numerous species characteristic of other grassland areas are 

 present here, the major dominants are distinctive, including Agro- 

 pyron spicatum, Festuca idahoensis, and Elyimis condensatus. Pos- 

 sibly much of the sagebrush dominance in this region is only the 

 result of grazing, and certainly the dominance of the annual, 

 Br omits tectorum, results from fire and grazing as it does south- 

 ward in the Great Basin. 



The Palouse and California grasslands, in contrast with the major 

 areas, are products of winter, rather than spring and summer, 

 precipitation. 



Aspect Dominance.— Probably no other formation has such 

 marked variations in appearance through the growing season. 

 Since not all the grasses mature at once, there are times when 

 simple observation might lead to incorrect conclusions as to their 



