234 



CLIMAX FORMATIONS OP NORTH AMERICA. 



"In discussing the plant successions it is necessary to deal with smaller 

 communities than those mentioned in this table. It is also impracticable 

 to discuss the Sand-hills Mixed and some of the minor communities in this 

 brief svunmary. 



Types of the vegetation in Tooele YaUey, Utah, and their dominant species, in relation to aver- 

 age soil moisture and salinity conditions.''- 



'The term "dry" as here applied to the soil indicates that its water content is below the wilting coefficient. 

 The term "moist" implies that moisture available for plant growth (above the wilting coefficient) is present. 



'Further investigation of the vegetation of the Great Basin region is needed before definite ecological raak can 

 be assigned to the grass-flat and the salt-flat communities. 



"The accompanying bisect presents the principal plant associations and the 

 moisture and salt conditions characteristic of each. It is arranged to show 

 the natural succession. The lower part of the sketch illustrates the develop- 

 ment following Allenrolfea when a sufficient amount of fresh water is added to 

 modify the salt content without, at the same time, markedly changing the 

 moisture conditions. The salt content recorded under each association is an 

 approximate mean condition and gives no idea of the variation encountered 

 under each association (plate 53). 



"Lake Bonneville, a large fresh-water lake, originally covered the valley to 

 a depth of 1,000 feet above the present level of Great Salt Lake (4,200 feet). 

 In the early stages of recession the lake was fresh and did not become salt imtil 

 most of the land area at present occupied by the Artemisia association had 

 been exposed. The Artemisia association lies, for the most part, 300 feet 

 above the present lake level. The Atriplex and Kochia areas he, for the most 

 part, from 20 to 300 feet above the present lake level, and the Salicomia, 

 Allenrolfea, Distichlis, Sporobolus, Chrysothamnus, and Sarcohatus areas within 



