THE SHORT-GRASS PLAINS. 141 



times with two of them, but also as a pure dominant over large areas. Bul- 

 bilis stands next to Bouteloua in importance, and the two, singly or together, 

 constitute the fundament of the association. Bulbilis is largely restricted to 

 the eastern part of the area, while Muhlenbergia and Hilaria are found chiefly 

 in the western. This results in a differentiation into two halves, an eastern, 

 consisting almost wholly of Bouteloua and Bulbilis, and a western, made up of 

 Bouteloua with Muhlenbergia or Hilaria. The former is typical of western 

 Kansas and Oklahoma and the Panhandle of Texas; the latter is found in 

 southern Colorado and the northern half of New Mexico and Arizona. 



Any one of the five dominants may appear as a pure community, but this 

 is rare for Muhlenbergia and infrequent for Bouteloua hirsuta. Hilaria often 

 dominates extensive areas in New Mexico and Arizona, and in the Great 

 Basin where the sagebrush and short-grass are in contact. In the latter, 

 especially, it is more or less subclimax in nature and mixes with Bouteloua 

 gracilis as the climax is approached. Bouteloua hirsuta is characteristic of 

 sandy areas and rough gravel or limestone hills, and is most abundant in 

 sandhills. While it is an important dominant in the desert plains association, 

 it is secondary on the plains proper, and is often to be regarded as subclimax. 

 Muhlenbergia is a fairly constant associate of Bouteloua gracilis in Colorado, 

 New Mexico, and Arizona. It has been found in pure stands of considerable 

 extent only in the latter. It bears much the same relation to Bouteloua that 

 Bulbilis does, and hence rarely occurs with the latter. 



The southern Great Plains are characterized by Bouteloua gracilis and 

 Bulbilis dactyloides in varying relations. As a rule they are associated, but 

 either may occur as a pure dominant. They may meet on nearly equal terms 

 or may exhibit varying degrees of relative abundance. In the eastern portion 

 of the association Bulbilis is usually controlling and Bouteloua secondary, 

 though this relation is often reversed on the Staked Plains of Texas and New 

 Mexico. From Colorado southward, Bouteloua is generally controlling and 

 Bulbilis secondary. Where Bulbilis is predominant the sod is dense and the 

 grama grass is scattered through it more or less abundantly. Grama typically 

 forms an open sod, even where it is dominant, but the persistent sod habit 

 of the buffalo-grass causes the latter to appear in compact mats a few feet 

 to several yards or more in diameter. The open grama turf dotted with mats 

 of Bulbilis is so characteristic over much of the Great Plains that it was sup- 

 posed to be the rule. In the summer of 1918, however, buffalo-grass was 

 found to be either controlling, and sometimes pure, or to meet grama on 

 equal terms throughout southwestern Kansas and western Oklahoma. This 

 is in accordance with the water relations, as discussed below. 



Grouping of dominants.— The groupings of short-grasses are relatively few 

 and simple. Bouteloua gracilis is normally present in all of them and usually 

 as the predominant species. Most of the groups consist of two dominants 

 only, for example, Bouteloua-Bulbilis, Bulbilis-Bouteloua, Bouteloua-Hilaria, 

 Bouteloua-Muhlenbergia, and Bouteloua gracilis-B. hirsuta. Bouteloua gracilis 

 also occurs with B. hirsuta and Muhlenbergia, and with Hilaria and Muhlen- 

 bergia. On the plains of Oklahoma and Texas, Bouteloua racemosa is a fre- 

 quent associate of Bulbilis-Bouteloua and sometimes appears to be a codomi- 

 nant. North and northeast of the associational area Bouteloua and Bulbilis 

 become constituents of the mixed prairie, forming a layer beneath Stipa and 



