OVERGRAZING. 295 



Hurtt, 1917), while intensive experiments have been made at Mandan and 

 Ardmore by the Office of Dry-Land Agriculture (Sarvis, 1919). Whether 

 carrying capacity is determined by general experience or measured by actual 

 experiment, the extension and use of the measures obtained depend upon the 

 composition of the grazing type and the abundance and size of the dominants, 

 as determined by the quadrat method. The degree of carrying capacity de- 

 pends, first, upon the number and kind of the dominants associated in any 

 grouping; second, upon their density; and third, upon the abundance of sub- 

 dominants. Once it has been found for any particular grouping by experience 

 or experiment, it can be extended to the same or similar types in other regions 

 by using the dominants as indicators and checking this by means of the quad- 

 rat as a measure of composition, abundance, and yield. This is especially 

 true where protection inclosures are employed, since they readily show the 

 increase possible in the particular grazing type. 



Present and potential carrying capacity The present capacity of a par- 

 ticular grazing type is determined by its structure and the degree to which it is 

 overgrazed. Its potential capacity depends upon the recovery possible 

 under proper grazing management and the increased utiUzation brought 

 about by supplementary forage crops. The actual present capacity of a 

 range is determined by the yield during drought periods, while the potential 

 capacit}'^ is suggested by that of wet periods, which may be several times 

 greater. Wliile the open range in the grassland cUmax has been more or less 

 constantly overgrazed since the advent of the buffalo, the evidence indicates 

 that the carrying capacity was higher for a decade or two after the disappear- 

 ance of the buffalo and that it has steadily decreased up to the present time, 

 except in the regions where settlement and fencing have brought about some 

 degree of protection. During the last decade, the carrying capacity of ranges 

 in the national forests has been increased 20 per cent or more as a result of 

 grazing control, and it appears certain that the open range will permit much 

 greater improvement. The amount of the latter will depend upon the differ- 

 ence between the present and the potential capacity. A mixed type of tall- 

 grasses and short-grasses will have a higher potential capacity than one of 

 either grass-form alone, though overgrazing may reduce its present yield 

 practically to that of a short-grass type. The mixed prairie of North Dakota 

 has been shown by Sarvis (1919) to have a carrying capacity of 1 to 7 during 

 the drought years of 1917-18, while it might well equal 1 to 3 during wet 

 periods. The short-grass type of the Texas Panhandle has an average capac- 

 ity of 1 to 12 (Smith, 1899: 11), while in New Mexico it seems to be somewhat 

 lower (Wooton, 1908:27). In the desert plains, the BouUloua eriopoda 

 consociation has a capacity of 1 to 20 (Jardine and Hurtt, 1917: 17), while 

 Wooton (1916:22) assigns a similar value to the Boutelona-Aristida com- 

 munities of the Santa Rita Reserve. The short-grass types are grazed for a 

 longer period, however, and their comparative canying capacity is relatively 

 higher. 



OVERGRAZING. 



Nature. In practice, a range is regarded as being overgrazed only when its 

 carrying capacity has actually decreased. Such a test is often indefinite 

 because of the conditions under which the stock industry is carried on, and 

 this explains the divergent views as to the condition of particular ranges. 



