284 THE STUDY OF PLANT COMMUNITIES * Chapter X 



which seem equally permanent, are found only in special habitats. 

 Succession, as ordinarily conceived, is almost nonexistent since re- 

 action of the vegetation is negligible. Unless there is marked dis- 

 turbance, most communities remain indefinitely unchanged and 

 dominant in their special habitats. It seems best, therefore, to pre- 

 sent the characteristics distinguishing the four deserts and to indi- 

 cate the dominant vegetation in different habitats with less than 

 the usual emphasis upon climax or its relationships. What follows 



,-&:■ .■,■*. . '■ . » ■■■■■>■• -■■■■ ■■'■'■'' v- :V * %■ 



FIG. 149. Sagebrush desert (Arte?nisia tridentata) northwest of Reno, 

 Nev.— Photo by W.D. Billings. 



is adapted almost entirely from Shreve's 238 excellent summary of 

 desert vegetation except for the distinction made here between 

 Sagebrush and Desert Scrub Formations. 



Sagebrush Formation- Great Basin Desert— There is physio- 

 graphic, climatologic, and vegetational unity throughout all the 

 Great Basin area north of southern Nevada and southern Utah. 

 The wide valley floors, lying at about 4,000 feet, are interrupted 

 by numerous ridges, often rising to more than 8,000 feet, and de- 

 pressions of the playa type. The meager rainfall, four to eight 

 inches, is heaviest in spring but may come in any season. Tempera- 



