22 



BULLETIN 791, U. S. DEPARTMENT OF AGRICULTURE. 



If this is not done, the retrogression of the vegetation to a pure sec- 

 ond-weed stage, or, indeed, to tiie first-weed stage, is inevitable. 



THE PORCUPINE-GRASS- YELLOW-BRUSH CONSOCIATION. 



As a result of the serious overgrazing in the Wasatch Mountains 

 prior to the inclusion of the lands in the Wasatch Forest in 1905, the 

 wheat-grass consociation was much injured in many localities. Where 

 the fertility of the soil was not appreciably impaired after the de- 

 struction of the subclimax grass 

 cover, the wheat grasses soon re- 

 establish themselves; but where ap- 

 preciable erosion took place or where 

 a considerable proportion of the sol- 

 uble soil nutrients was leached out, 

 the wheat-grass species failed to re- 

 occupy the lands. On the seriously 

 impoverished soils, only a sparse 

 stand of short-lived plants at first 

 gained a foothold ; but on areas where 

 the fertility and the water-holding 

 capacity of the soil were onlj- slightly 

 impaired, grasses, notably small 

 mountain porcupine grass {Stipa 

 minor) (fig. 8), and its ever-present 

 associate, yellow brush {Chrysotham- 

 nus lanceolatus ), predominated. 

 Wliere the soil was more seriously 

 depleted, blue grasses, fescues, brome 

 grasses, and others were invariably 

 associated with porcupine grass and 

 yellow brush. 



After the destruction of tlie wheat- 

 grass consociation by overgrazing, a 

 large proportion of the entire cover 

 was then either of the ea'rly or 

 late weed stage; but as a result of correcting the destructive 

 factor of overstocking, the porcupine-grass-j^ellow-brush type now 

 constitutes the most extensive consociation of relatively high-carry- 

 ing capacity in the high mountain region. 



Small mountain porcupme grass and the local congeneric species 

 grow as bunch grass, and the intervening space is occupied by other 

 grasses and nongrasslike plants. T\rhere the soil has undergone 

 only slight change physically and chemicalh'- as compared with its 

 condition when occupied b}^ the wheat-grass cover, the stand of small 

 mountain porcupine grass and yellow brush is full, and the stand 



•Small Moun+a.r 

 (Sf'pq. 



Porcupine^rsSS. 

 •ninor) 



Fig. 8.- — The dominant species of the 

 porcupine-grass-yell ow-brusli conso- 

 ciation. 



