286 THE STUDY OF PLANT COMMUNITIES * Chapter X 



sandy or clayey, with the carbonate layer at a deeper level and 

 with a minimum concentration of salts. 21 



The controlling effect of salts on community structure has been 

 amply demonstrated for different parts of the area. 21 ' 98 > 134 Zonal 

 patterns around playa lakes are the same everywhere (see Fig. 86). 

 Where flooding is periodic and salt content excessive, vegetation 



~~i 



FlG. 151. Creosote bush (Larrea divaricata) with Franseria dumosa in as- 

 sociation as is typical of much of the Mojave Desert. Numerous desert an- 

 nuals can be seen.— Photo by W. D. Billings. 



is absent or dominated by glasswort (Salic ornia spp.) or iodine 

 bush (Allenrolfea occidentalis). With somewhat less salt, shadscale 

 and greasewood (Sarcobatus vermiculatus) or red sage (Kochia 

 vestita) are dominant. Away from the playas on soils with a mini- 

 mum of salts, sagebrush may be the major species. 



Many other species occur, of course. They are mostly semi- 

 shrubs with the same growth form. There are numerous species of 

 Atriplex and Artemisia. Chrysothamnus puberulus, Grayia spin- 

 osa, Coleogyne ramosissima, Eurotia lanata, Purshia tridentata, and 

 others are variously associated with the major species or sometimes 



