68 BULLETIlSr 791, U. S. DEPARTMENT OF AGRICULTUEE. 



probably more fully utilized by cattle and horses than by slieep, 

 are better suited for the grazing of sheep than the turfed wheat-grass 

 areas. The grazing both of cattle and sheep on the bunch-grass lands, 

 as well as on the opened-up stands of the turfed areas, insures the 

 maximum economic use of the entire forage crop. 



THE PORCUPINE-GRASS-TELLOW-BEUSH CONSOCIATION. 



14. The small-mountain-porcupine-grass and yellow-brush cover is 

 the second highest and the most stable forage type. Accordingly, 

 j)orcupine grass and yellow brush are among the first perennial plants 

 to occupy wheat-grass areas where unfavorable conditions have killed 

 out the wheat-grass cover but where the soil has not been depleted 

 so much as to favor the establishment of a pure or predominating 

 weed type. 



15. Because of the exposure of a considerable portion of the soil 

 surface, precipitation readily percolates into the soil, reaching to or 

 beyond a d^pth corresponding to the lower extension of the deep- 

 rooted species. Accordingly, an admixture of shallow-rooted and 

 deep-rooted species is characteristic of this consociation. The water- 

 holding capacity of the soil, particularly the upper foot or so, is less 

 in this than in the wheat-grass cover. 



16. In the higher development of the porcupine-grass and yellow- 

 brush cover a scattered stand of wheat grasses, and usually a con- 

 spicuous presence of blue grasses, and not uncommonly of fescues, is 

 characteristic, though these plants are never dominant. In the lower 

 or earlier development, the brome grasses, and not uncommonly the 

 fescues, in association with numerous nongrasslike perennials, are 

 conspicuous. The higher development is further characterized by 

 fewer weed or nongrasslike species than the lower development. 



17. Small mountain porcupine grass, like the majority of the 

 blue grasses and fescues, obtains its moisture supply chiefl}^ from the 

 first foot of soil. Yellow brush and other deep-rooted species, such 

 as loco and wild bean, extend their roots about three or four times 

 as deep. Many plants are present whose root" systems are inter- 

 mediate in length, so that the available water supply from the sur- 

 face to a depth of 3 feet or more is rather uniformly exhausted as 

 the season advances. 



18. The most reliable indication of the presence of conditions ad- 

 verse to the perpetuation and maintenance of the porcupine-grass- 

 yellow-brush cover, including the typical associated species, is the 

 replacement of one or both of the dominants by aggressive non- 

 grasslike plants. '\'\'Tiere the depletion of the soil is gradual and not 

 too severe, blue foxglove, sweet sage, and yarrow are the first to gain 

 dominion over the soil, the increase in these species being associated 

 with an increase in brome arass, and in some cases in fescues. 



