THE BASIN SAGEBRUSH. 157 



by Artemisia tridentata, A. cana, and Gviierrezia. Few other associations of 

 the West exhibit such a large number of dominants or such a variety of group- 

 ings. It is also the most xerophytic of all climax associations, with the excep- 

 tion of the Larrea-Prosopis desert, and is unique in its general halophytic 

 character. The greatest development of dominants is in the climax mass, 

 from which they shade out toward the margins, being represented in the out- 

 post conmiunities by a single species. The haloid dominants are the least 

 extensive, and the lower non-haloid forms, such as Gviierrezia, have the 

 widest range. In fact, A. cana, A. trifida, Eurotia lanata, and Gviierrezia 

 sarothrae are so completely at home in the mixed prairies or short-grass plains 

 that it has seemed desirable to treat them as societies where they occur in 

 these associations. Like most of the western associations, the sagebrush has 

 received little quantitative study as yet, and it is possible to deal only with its 

 outstanding features and to suggest some of its more obvious correlations. 



CONSOCIATIONS. 

 ABTmaBIA TRIDENTATA. ARTEMISIA CANA. GrATIA SPINOSA. 



Atriplex contertifoua. Artemisia arbuscula. Gutierrezia sarothrae. 



Chrysothamnus nauseosus. Artemisia trifida. Tetradtmia spinosa. 



Chrtsothamntts nsciDiFLORUs. Artemisia riqida. Eurotia lanata. 



Atriplex canescens Artemisia spinescens. 



The most important as well as characteristic of all the dominants is Arte- 

 misia tridentata. It is also one of the most widespread, ranging from Saskat- 

 chewan to Nebraska, Mexico, CaUfomia, and British Columbia. In this 

 respect it is equaled by Eurotia lanata and Chrysothamnus nauseosus, and 

 excelled by Gviierrezia sarothrae, which extends eastward to central Kansas. 

 Atriplex canescens is of nearly as wide range, but it appears to be lacking in 

 Canada. Atriplex confertifolia and Chrysothamnus viscidiflorus are somewhat 

 more hmited, as is the case with Grayia spinosa, Artemisia cana, and the 

 remaining species of Artemisia. Naturally, the range of these as climax 

 dominants is much more restricted, and is almost wholly confined to the 

 Great Basin proper (plate 33). 



Rank and grouping. ^The number of dominants in the association is so 

 large and their equivalences so close that a large number of groupings occur. 

 In the endeavor to determine the relative importance of the dominants and of 

 the various mixtures, a simamary has been made for all locahties visited in 

 the sagebrush association in 1907, 1909, and from 1913 to 1918. The total 

 number of locahties was 416, including a few duphcated in different years. 

 The sequence of the various dominants is shown by the following table : 



Total number of localities 416 



Artemisia tiidentata 314 



Atriplex confertifolia 142 



Chrysothamnus 140 



Atriplex caneecens 66 



Grayia spinosa 54 



Gutierrezia sarothrae 45 



Tetrad j-mia spinosa 37 



Eurotia lanata 15 



Artemisia spp. (except A. tridentata) . 61 



Artemisia tridentata was found 60 times in pure stands stretching over many 

 miles, often for 20 to 30 miles without interruption. Atriplex confertifolia 

 was met but 10 times in extensive pure areas, though it is very often found 

 on hillsides and mountain slopes in pure communities a few miles long. While 

 the more halophytic and hence subclimax species of Chrysothamr\us make 

 pure stands, sometimes covering several to many square miles, the climax 



