14 BULLETIN 367, U, S. DErAETMEXT OF AGEICULTUKE. 



portance as the writer was able to locate it. It may be undesirable 

 from some standpoints to try to separate these associations, but to 

 do so has seemed tp give a little clearer conception of the condi- 

 tions existing on the reserve, even though the ci'owfoot grama will 

 go higher and the needle grasses do go considerably lower and not- 

 withstanding the fact that other grasses occur freely in both asso- 

 ciations and seem to link the tAvo. 



The needle-grass association consists of a number of important 

 perennial grasses, of which Aristkla divaricota and what is probably 

 A. scahra are the most abundant (PL IV, fig. 1), hence the name 

 here suggested. The next most important grass is Bouteloua fJl- 

 formis^ which frequently makes up from one-fourth to one-third 

 of the assemblage. Toward the upper limit of the belt this grass is 

 apt to be replaced by B. chondrosioides. Hairy grama {Bouteloua 

 hirsuta) also occurs on the rockier hills, and Texas curly mesquite 

 {Hilar ia cencJiroides) is not uncommon at the lower side of the 

 zone. 



Wherever the needle-grass association is entirely killed out the 

 six- weeks grasses and annuals first take the ground, and then the 

 short-lived perennial gramas appear in abundance before the longer 

 lived perennial Aristidas become established. As the greater part 

 of this belt that is inclosed is grazed by cattle and horses, the various 

 conditions mentioned may be found at different places in the differ- 

 ent pastures. Wherever the stock congregate most the six-weeks 

 grasses and annuals abound. AAliere this condition of local over- 

 grazing is relieved some step in the sequence of complete replace- 

 ment of the association occurs. 



Additional perennial grasses in this association are Texan timothy 

 {Lycurus fhleoldes)^ tall, or sicle-oats, grama {Bouteloua curtipen- 

 dula), Eragrostis lugens^ Elionurus harhiculmis^ and Trachypogon 

 montufari., while numerous spring and summer herbaceous annuals 

 and perennials add considerable to the forage crop. The lower 

 limit of these needle grasses is not the limit of the association, since 

 they are common in patches in the crowfoot-grama association and 

 follow down the dry watercourses, or arroyos, to the very lowest 

 parts of the inclosed area. In many places in the crowfoot-grama 

 association they may constitute as much as 25 per cent of the forage 

 present on the ground. Whether or not they will gradually crowd 

 downhill and finally replace the crowfoot-grama association remains 

 to be seen, but at present the writer believes they require a little 

 more water than the crowfoot grama and will hardly be able to en- 

 tirely replace that association as it now exists on the reserve, no 

 matter how long the area may be protected. No data are available 

 relative to the crop of spring feed upon this area, but it is doubtless 

 of no great importance except where overgrazing has occurred. 



