54 BULLETIN 791, U. S. DEPARTMENT OF AGRICULTURE. 
watershed, it is essential that stock permitted on this type be handled 
in accordance with the most approved methods. If serious erosion is 
to be prevented, the lands should be grazed very lightly or not at 
all until plants of the second-weed stage have gained a foothold. 
THE EFFECT OF GRAZING ON PLANT SUCCESSION. 
The grazing of live stock may, under certain conditions, either re- 
tard or promote the development of a plant cover and cause either 
retrogression or progressive succession. 
DESTRUCTIVE GRAZING AND ITS RELATION TO EROSION. 1 
The highest grazing efficiency consists in getting the greatest 
possible use out of the range from year to year. Any system of graz- 
ing, therefore, which decreases the carrying capacity of the lands so 
that the forage production is decreased from season to season may be 
classed as destructive. If such a method is continued, the ground 
cover will be partly or wholly destroyed, a condition which is almost 
invariably associated with erosion. 
While it is probably true that the extent of surface run-off and 
erosion is largely determined by climate, topography, and soil, the 
combined influence of these factors on the high mountain grazing 
lands of the West is not such as to cause serious soil depletion except 
where the vegetative cover has been badly impaired. A typical cast- 
of overgrazing, indicating the relation of the vegetative cover to 
erosion, is shown in figure 21. 2 The more important facts brought 
out in figure 21 may be summarized as follows : 
1. Where the original cover remained intact, as in section B to the 
extreme left in the figure, practically no erosion occurred. Partial 
destruction of the vegetation (section B to extreme right) was accom- 
panied by moderate erosion, while serious destruction of the cover 
(section A) was associated with erosion of a most serious character. 
2. The colonization on the moderately depleted areas (section B 
to extreme right) consists essentially of typical second-weed-stage 
plants, while on the very sparsely colonized blocks (section A) the 
vegetation is composed either of the first-weed-stage plants or of 
1 For further information as to the relation of grazing to erosion, see Sampson, Arthur 
\V., and Weyl, Leon EL, " Range Preservation and Its Relation to Erosion Control on 
Western Grazing Lands," U. S. Dept. of Agr. Bui. No. 675, 1918. 
2 The area represented lies at an elevation of about 10,000 feet, has a western ex- 
posure, and an average slo*pe of approximately 11 per cent. Until 1905, when the lands 
came under governmental control, the range had been subject to heavy overgrazing by 
all classes of stock. Since 1905, the area has been subject to moderate grazing by cattle 
and sheep. As a result, considerable revegetation has taken place whore the original 
cover remained more or less intact, and where little or no erosion occurred. The badly 
eroded areas, however, have improved relatively little in carrying capacity during the 
past 10 or 12 years (1905-1917) of moderate grazing, and now they furnish only a small 
amount of inferior forage. 
