SECOND OR LATE WEED STAGE 113 



turf-forming species like blue foxglove {Pentstemon procerus)^ 

 yarrow {Achillea lanulosa), and sweet sage {Artemisia discolor) 

 predominate. 



Destruction of the Porcupinegrass-Yellowbrush Cover. — So 

 long as the porcupinegrass-yellowbrush cover retains its density 

 of stand, or, better still, if it is being replaced by the wheat- 

 grasses, it is perfectly clear that the lands are not being misused. 

 If, on the other hand, the type is being supplanted by brome- 

 grass, or, more seriously still, by foxglove, sweet sage, and yarrow, 

 or other plants of the second weed stage, there is indisputable 

 evidence of the depletion of the area. In a short time the waning 

 forage crop at this stage of depletion will be reflected in the con- 

 dition of the stock grazed and in the increased erosion of the soil. 



Forage Production. — Because of the large variety of palatable 

 plants that are associated with the porcupinegrass-yellowbrush 

 cover, this type in its highest stage of development is probably 

 the most desirable, all classes of stock considered. Since the 

 forage is composed of a mixture of grasses and weeds, with the 

 former distinctly predominating, the highest grazing efficiency is 

 usually obtained through " common use," that is, the combined 

 grazing of cattle, horses, and sheep. 



SECOND; OR LATE WEED STAGE 



Where unfavorable conditions for the growth of the porcupine- 

 grass-yellowbrush cover have not been such as materially to 

 lower the fertility of the soil, shallow-rooted but often turf- 

 forming perennial weeds of the early second weed stage are the 

 natural successors. The most conspicuous and characteristic of 

 these are blue foxglove, yarrow, and sweet sage (Fig. 32), On the 

 other hand, where the porcupinegrass-yellowbrush cover is 

 suddenly destroyed and a considerable portion of the upper dark 

 soil is carried away, the vegetation consists chiefly of annual 

 plants characteristic of the first or early weed stage. 



A somewhat large number of species are associated with the 

 foxglove-yarrow-sweet sage type, but they are usually second- 

 ary in abundance. They are mostly short-Hved, broad-leaved 



