PLANT SUCCESSION AND RANGE MANAGEMENT. 55 
species that appear Aery early in the succession of the second-weed 
stage. The blocks upon which the cover was only slightly impaired 
axe occupied essentially by the subclimax wheat grasses. 
3. The root system of the vegetation as a whole, as shown in the 
cross-section view of figure 21, is the sparsest and most superficial 
on the seriously eroded blocks, intermediate both as to depth and 
density on the moderately eroded areas, and deepest and most abun- 
dant on the least eroded and most highly vegetated blocks. 
Chemical analyses of the soil have clearly shown that the fertility 
is roughly in proportion to the extent of the soil depletion, the least 
soil eroded being the most fertile. In these tests the samples of non- 
eroded soil contained an average of approximately four times more 
organic carbon, three times more total nitrogen, and four times more 
total organic matter than did the eroded samples. Likewise the 
water-holding power in the soil samples from the noneroded blocks, 
when saturated, was greater by 9 per cent than in the samples from 
the eroded blocks. 
From these facts it is evident that any system of grazing which 
results in the destruction of the ground cover and at the same time 
permits erosion to gain headway, not only immediately decreases the 
carrying capacity of the lands but prevents the establishment of the 
more permanent cover for an indefinite period — in some instances 
possibly for 50 years or more. 1 The translocation of the upper few 
inches of the surface layer of soil, with its comparatively rich im- 
pregnation of organic matter, causes the usual reversion of the vege- 
tation to a lower successional stage, not uncommonly the first-weed 
stage. Under such conditions the former dominance of the sub- 
climax species will not again appear until the original fertility of 
the soil has been reestablished, which is possible only after the appli- 
cation of many years of judicious range management. The contin- 
uance of grazing without regard for the growth requirements of the 
vegetation causes further soil depletion. 
FORAGE PRODUCTION ON DRIVEWAYS AND BED GROUNDS. 
The use year after year of established driveways and bed grounds 
for stock furnishes noteworthy instances of retrogressive succession. 
While it is true that the majority of the driveways on the National 
Forests were most seriously depleted before the lands came directly 
under the control of the Government, and that since that time many 
have improved somewhat in productivity, generally they support 
only a sparse cover of inferior transitory vegetation. Established 
bed grounds are usually depleted in proportion to the length of time 
1 Shantz, IT. L., " Plant Succession on Abandoned Roads in Eastern Colorado," Jour- 
nal of Ecology, Vol. V, No. 1 : 19, 44, 1917. 
