68 BULLETIN 791, IT. S. DEPARTMENT OF AGRICULTURE. 
probably more fully utilized by cattle and horses than by sheep, 
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 PORCITPIXE-GRASS-TELIX)W-BR"CSH COXSOCIATIOX. 
14:. The small-mountain-porcupine-grass and yellow-brush cover is 
the second highest and the most stable forage type. Accordingly, 
porcupine 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 depth 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 chiefly 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. Where 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 jrrass. and in some cases in fescues. 
