136 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA. 



a careful search was made for protected areas, especially along railways, in 

 regions where Stipa or Agropyrum would be expected. The result was the 

 discovery of one or both in or near practically all pure Bouteloua or Bulbilis 

 communities found in the Dakotas, Montana, Wyoming, Nebraska, and 

 Colorado. Similar results were obtained for both dominants over a large 

 part of the sagebrush association from Oregon to Colorado, and for Stipa 

 throughout California. Indeed, what was once the climax association of 

 Stipa over the interior valleys from San Diego to Mount Shasta is now repre- 

 sented by widely scattered relicts enabled to persist by chance protection. 

 It was to be expected that such widespread response to grazing would have 

 been noticed by other observers, and this has proved to be the case. Williams 

 (1898 : 54, 55) found that Agropyrum, when too closely grazed, made most of 

 its growth by underground stems, and very few if any fertile culms were 

 developed. He also observed that Stipa, when kept closely grazed, seldom 

 seeded in quantity. Wooton (1912 : 58) says that Stipa pennata neomexicana 

 and S. comata "are relished by stock and are of especial importance because 

 they appear at a time when most of the other grasses are dead and dry. Appar- 

 ently they do not reproduce readily and since they are now rarely allowed to 

 go to seed, they are probably being gradually exterminated wherever stock 

 can get at them." The Forest Service bulletin on range grasses (1914 : 175) 

 states that in parts of northern New Mexico Stipa comata is in danger of exter- 

 mination because it is so closely grazed in spring and early summer that it is 

 not given a chance to seed. Wooton and Standley (1915 : 66) make the 

 following statement about these species: "Both are valuable range grasses; 

 neither, however, reproduces well, but is soon killed by overstocking and 

 replaced by needle grasses." 



The fact that Stipa and Agropyrum are taller and more conspicuous in wet 

 seasons suggested the possibility that they were greatly reduced or lacking in 

 dry years. Throughout the association, however, they proved as abundant 

 and universal in the dry years, 1916 to 1918, as in the exceedingly wet year of 

 1915. The only evident response to drought was a marked reduction in height 

 and in the number of flower stalks, a reduction which affected Bouteloua as 

 much as Stipa, though hardly as much as Agropyrum. This was further con- 

 firmed by a scrutiny of reports on grassland in the Great Plains from 1889 to 

 1915 and by field notes from 1897 to 1918. All of these agreed in showing the 

 constant association of tall-grasses and short-grasses throughout the region, 

 not only for the wet phases of the three climatic cycles but for the dry periods 

 as well. Since the latter included two of the severest drouths recorded, it is 

 certain that the tall-grasses and short-grasses are regularly codominants of 

 the association, except where grazing interferes. In connection with the 

 grazing experiments discussed later, permanent protected quadrats have been 

 established in representative areas of the association for the purpose of secur- 

 ing an exact record of the effect of grazing and of protection, as well as of the 

 dry and wet phases of the climatic cycle (plate 24). 



Range. — The mixed prairies occur from central North and South Dakota, 

 central Nebraska, and northwestern Kansas, throughout Montana and Wyo- 

 ming to the Rocky Mountains, and southward in Colorado along the foothills 

 of the Front Range. They extend well north into Saskatchewan and Alberta 



