32 BULLETIN 791, U, S. DEPARTMEITT OF AGRICULTURE. 



plants make up the ground cover in somewhat equal proportions. 

 The highest development of the porcupine-grass-yellow-brush cover 

 is indicated by a scattered stand of wheat grasses, a rather conspicu- 

 ous presence of blue grasses {Poo) , and a somewhat smaller amount 

 of fescue grasses. The lower development of the type in question is 

 characteristically indicated by the conspicuous presence of brome 

 grass, and not uncommonly of fescue grasses, with the addition of 

 several perennial nongrasslike plants, among which blue foxglove, 

 sweet sage, and yarrow are the most common. 



So long as porcupine grass and yellow brush, including the typical 

 associated species, hold their place in competition with plants of 

 lower successional stages, or yield to the invasion of plants higher 

 in the cycle of succession, like the wheat grasses, it is perfectly clear 

 that the range is not being misused. If, on the other hand, the por- 

 cupine-grass-yellow-brush consociation is being replaced by brome 

 grasses, fescues, and more especially by blue foxglove, sweet sage, 

 yarrow, and other plants of the second weed stage, there is indis- 

 putable evidence of the deterioration of the range. 



In view of the large variety of palatable plants associated with the 

 porcupine-grass-yellow-brush cover, the highest possible development 

 of this type is probably the most desirable of any for the grazing of 

 all classes of stock. Since the forage crop is composed both of 

 weeds and grasses, with the latter distinctly predominating on the 

 better developed types, the highest grazing efSciency is obtained 

 through "common use," that is, through the combined grazing of 

 cattle, horses, and sheep. 



THE FOXGLOVE-SWEET-SAGE- YARROW CONSOCIATION. 



Detailed quadrat data and extensive observations have shown that 

 when conditions unfavorable to growth are sufficiently prolonged 

 gradually to destroy the porcupine-grass-yellow-brush cover, but not 

 such as seriously to change the condition of the soil, shallow- 

 rooted perennial weeds of the second weed stage, notably blue fox- 

 glove {Pentsteirwn frocei'^s)^ sweet sage {Arteinisia discolor), and 

 yarrow {AcMUea lanulosa) are the natural successors. On the other 

 hand, where the porcupine-grass-yellow-brush cover is suddenly de- 

 stroyed and considerable portions of the upper soil layer carried 

 away, as often takes, place where live stock* are injudiciously handled, 

 the immediate successional cover consists chiefly of annual plants 

 characteristic of the first or early weed stage, with or without an 

 admixture of perennial species. 



In the gradual elimination of the porcupine-gTass-yellow-brush 

 cover perennial weed species usually gain a foothold shortly after 

 the ground is exposed or when the roots of the gi-ass and brush cover 



