PLANT SUCCESSIOK AlTD RANGE MANAGEMENT. 67 



plants. The bunched wheat-grass areas, on the other hand, are 

 seldom pure in stand, and plants other than grasses usually occupy 

 the soil space between the tufts. The nongrasses occur in varying 

 density, depending chiefly upon the available soil water content. 



7. The root-absorbing surface of the densely turfed wheat 

 grasses is relatively superficial, the greater proportion of the roots 

 being confined to the upper 8 inches of soil. The roots of the 

 bunched species typically extend to a depth of 3 feet or more, hence 

 their moisture supply is largely gathered well below the depth at 

 which the turfed species obtain theirs. 



8. Precipitation percolates so slowly through the matlike surface 

 of the turfed wheat-grass area that only a small portion of the rain- 

 fall, especially that which comes during the growing season, pene- 

 trates beyond the lower depths of the sod. Accordingly, other plants, 

 especially deep-rooted species, fail to become established in competi- 

 tion vvdth the turfed wheat grasses. 



0. Precipitation percolates deeply on the rather exposed soils of the 

 bunch-grass areas, and as a consequence both deep-rooted and shal- 

 low-rooted species, chiefly other than grasses, are commonlj^ found on 

 bunch wheat-grass areas. 



11. When a stand of bunch wheat grass is opened up there is an 

 some similar factor but not so as seriously to decrease the fertility 

 of the soil, the precipitation naturally percolates to a much greater 

 depth than where the turf remains intact. There follows an invasion 

 of certain deep-rooted species, the most typical and persistent of 

 which is yellow brush {C krysothamnus lanceolatus). As the wheat- 

 grass cover closes in about the yellow-brush plants, however, regard- 

 less of their luxuriance of growth and root development, they are 

 killed. This is due to the desiccation of the soil below the shallow 

 roots of the grass. 



11. When a stand of bunch wheat-grass is opened up there is an 

 increase in the density of other plant species. This secondary cover 

 is rather transitory both as to species and density. 



12. In terms of the amount of dry matter produced per unit of 

 surface, the turfed wheat-grass areas rank first, but owing to small 

 wheat grass {Agrojyyron dasystoxhyum) , the most conspicuous turfed 

 species, maturing somewhat earlier than the bunch grasses and at 

 the same time becoming less palatable when mature than the bunch 

 grasses, the turfed wheat-grass areas afford little, if any, more forage 

 than do the bunched wheat-grass areas. 



13. The wheat-grass type is the most permanent of any and with- 

 stands heavy grazing better than any other. Since the turfed 

 wheat grasses typically form a pure stand, this type of vegetation is 

 better suited for cattle and horses than for sheep. The virgin bunch- 

 grass lands, with their " combination " or mixed forage cover, while 



