54 BULLETIISr 791, V. S. DEPARTMENT OF AGRICULTURE. 



v/aterslied, 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.^ 



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.^ 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 



^ For further information as to the relation of grazing to erosion, see Sampson, Arthur 

 W., and Weyl, Leon H., " Range Preservation and Its Relation to Erosion Control on 

 Western Grazing Lands," U. S. Dept. of Agr. Bui. No. G75, 1918. 



2 The area represented lies at an elevation of about 10,000 feet, has a western ex- 

 po.sure, and an average slope 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 cattic 

 and sheep. As a result, considerable rvvegetation has taken place where the original 

 cover remained more or less intact, and where little or no erosion occurred. The badly 

 eroded areas, however, have improved relativel.y 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. 



