156 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA. 



e&mata. Atriplex canescens shows a similar behavior where Bouteloua forms a 

 closed sod, and A. conferti folia wherever Hilaria jamesii tends to become domi- 

 nant. The evidence of the replacement of sagebrush by the grasses during 

 the dry years of 1917 and 1918, either as a result of fire or clearing, or in conse- 

 quence of competition, has been so abundant as to indicate that a broad mar- 

 ginal belt of the climax is really subclimax, or at least tends to become such 

 during the dry phase of the climatic cycle. This subclimax belt is from 100 to 

 300 miles wide and extends all along the grassland contact from Oregon to 

 Montana and from Wyoming to Arizona. If placed under proper treatment, 

 it is felt that it can again be converted into the original grassland com- 

 munity. The significance of this for grazing is indicated in Chapter VI. 



The conversion of contiguous grassland into sagebrush has undoubtedly 

 been caused by overgrazing during the past fifty years, aided in a large meas- 

 ure by repeated fires. This is confirmed not only by evidence of the con- 

 trolling part formerly played by grasses in regions now covered by sagebrush, 

 but also by the persistence of the grass covering in areas more or less pro- 

 tected. This is particularly the case in the John Day Valley of eastern Oregon, 

 where the original Agropyrum sjncatum is almost completely displaced by 

 Artemisia tridentata over the range generally, while it persists in its former 

 dominance on rocky or inaccessible slopes. More recent evidence is afforded 

 by pastures in which Agropyrum has practically disappeared and weeds 

 abound, while contiguous protected areas show the pure stand of grass. 



Associations. The sagebrush formation is composed of two communities, 

 the Atriplex-Artemisia and the Salvia-Artemisia association. When the 

 climax formation was first recognized, it was supposed that it consisted of a 

 single association, the Atriplex-Artemisia halium. In attempting to determine 

 the relation of sagebrush to chaparral in California, it was found that the 

 community formed by Artemisia califomica, Salvia, and Eriogonum fasd- 

 cidatum showed a closer relationship to sagebrush than to chaparral. This 

 was first suggested by its constant position below the true chaparral and by 

 its more xerophytic nature. Further study showed the frequent contact 

 with the Artemisia tridentata association and confirmed the evidence afforded 

 by the similarity of the vegetation-forms with that of the sagebrush, and not 

 the chaparral. This was further supported by the discovery that the Cali- 

 fornia association bore the same relation to the Stipa grassland that the Great 

 Basin association does to the grasslands that touch it. As a consequence, 

 while the Salvia-Artemisia association is of limited extent in comparison with 

 the main association, it possesses all the characteristics of a distinct but 

 related community. It is less conspicuous because it has been more generally 

 disturbed by fire and overrun by such ruderal grasses as Avena and Bromus. 

 In protected areas where it retains its original character, it displays a marked 

 resemblance to some communities of the main association. 



THE BASIN SAGEBRUSH. 



ATRIPLEX-ARTEMISIA ASSOCIATION. 



Bange. Most of what has been said of the climax formation applies in 

 particular to this association. It covers the whole of the climax region, 

 except southern California and Lower California, and its outposts extend 

 into British Columbia, North Dakota, Kansas, and Mexico, as represented 



