PLANT SUCCESSIOl-T AND EANGE MANAGEMENT. 55 



species that appear very early in tlie succession of the second-weed 

 stage. The blocks upon which the cover was only slightly impaired 

 are 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.^ 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 



^ Shantz, H. L., " Plant Succession on Abandoned Roads in Eastern Colorado," Jour- 

 nal of Ecology, Vol. V, No. 1 : 19, 44, 1917. 



