284 GRAZING INDICATORS. 



CARRYING CAPACITY. 



Nature and significance.. The practical measure of tlie value of a range is 

 its carrying capacity. By this is meant the number of animals which can be 

 grazed upon it, expressed in terms of unit area, such as the number of head 

 grazed upon a section (640 acres), or the number of acres required to support a 

 single animal. It is usually expressed in terms of cattle as a basis, though it 

 is better to indicate it in terms of the animal to which the range is best adapted, 

 especially in the case of mixed grazing. As used at present, carrying capacity 

 is only a relative measure of the food value of a range or type. This is due to 

 several facts which introduce elements of uncertainty. Few grazing types are 

 uniform, either in density or composition, and the utilization of any dominant 

 depends to a great extent upon its associates. Even greater variation in 

 carrying capacity results from annual fluctuations in rainfall. On the animal 

 side, each kind of stock has its own preferences, as that of cattle for grass and 

 sheep for herbs, while horses and sheep utilize a forage cover much more 

 completely than cattle. Similar great differences result from the methods of 

 handling stock, especially with reference to the manner of herding by ages or 

 classes, or in the open or band system, with respect to water, salting, etc. 

 Carrying capacity may vary significantly with the breed of stock, and it is 

 obviously affected by winter feeding in regions of year-long range. Finally, 

 perhaps the largest element of uncertainty lies in the great variation in the 

 size and condition of stock when turned off of the range. As a consequence, 

 it is clear that more exact measures must be introduced, which will permit an 

 accurate comparison of different ranges and at the same time furnish a guide 

 to the varying conditions of the same range. The Forest Service (Jardine 

 and Hurtt, 1917) has already done much in this connection, especially with 

 respect to the extensive measurement of carrying capacity, while the office of 

 Dry-Land Agriculture (Sarvis, 1919) has developed a basic method of inten- 

 sive measurement. By the proper combination of these two methods, it will 

 be possible to secure an exact measure of the carrying capacity of all grazing 

 types, as well as of the fluctuations from year to year and under different 

 kinds of management. 



Determining factors. ^With respect to the plant cover alone, the carrying 

 capacity of a grazing type is summed up in the total amount of the annual crop 

 of forage. But the total yield must be interpreted in terms of value and 

 utihzation. Hence, it is necessary to take into account the composition of 

 the type, the palatability and nutritive value of the dominants and sub- 

 dominants, the duration and timeliness of the grazing season, and the effects 

 of the climatic cycle. Most of these factors are susceptible of exact measure- 

 ment, particularly the structure and yield of each type, the chemical com- 

 position of the dominants, and the response to annual variations in rainfall. 

 Their- practical significance, however, is subject to the test of actual graz- 

 ing, and hence it is imperative to take into account the relation of each to 

 the type of grazing indicated by the community. All of these relations are 

 summed up in grazing management, in which the kind of stock, the organi- 

 zation of the range, and the method of handling are the determining factors. 

 These are determined by the kind and amount of the annual yield of forage, 

 and in turn react decisively upon it. They are considered briefly in the fol- 



