24 BULLETIN 790, U. S. DEPAETMENT OF AGRICULTURE. 



iicreage. It is made up of (1) areas which produce no vegetation, 

 palatable to stock or so little that its use for grazing is not feasible ; 

 (2) areas which produce forage, but on which grazing is not prac- 

 ticable because of fallen timber, ruggedness, or too dense timber or 

 brush; and (3) areas of good range, inaccessible because the cost of 

 making them available for use is unwarranted by the value of the 

 forage to be secured. 



iWhere the lands of no grazing value are in one body it is not diffi- 

 cult to exclude them in estimating grazing capacity. jNIore often, 

 however, they are distributed in small areas, or small areas of graz- 

 ing value occur along drainage within larger waste areas. The out- 

 standing fact is that lands of no grazing value nvdj exist in sufficient 

 area to make figures for grazing capacity of a unit or Forest on an 

 acreage basis meaningless until these lands are excluded from the 

 estimates. 



The first problem in estimating grazing capacity of a large Forest 

 or of a large range unit, therefore, so far as there is a first problem, 

 is to get at the acreage which supports forage and can be gTazed. 

 A range classification of the Medicine Bow Forest, for example, 

 shows that 246,458 acres out of a total of 469,786 are not suited to. 

 the gi^azing of domestic stock. Pending a reconnaissance survey, 

 advantage should be taken of every opportunity in connection with 

 range inspection and range administration to secure similar figures' 

 for other forests. On many Forests the data must be collected in this 

 way if it is to be secured in a reasonable length of time. 



VAEIATION IN AMOUNT OF FORAGE PER ACRE. 



Variation in the amount of forage per acre on the land actually 

 used for grazing may be so great as to require from 10 acres to 100 

 acres to support a cow throughout the year. Such extremes rarely 

 occur on ranges of the National Forests after the area of no grazing 

 value is excluded from the estimates. A variation of 100 per cent, 

 however, not infrequently exists on a single unit. This fact confronts 

 the range examiner in making grazing-capacity estimates after he has 

 excluded acreage of no value for grazing. 



If forage production, or grazing capacity, were always unifonn 

 over any considerable acreage, close approximation in estimates 

 would not be exceedingly difficult ; but on the rugged mountain ranges 

 variation may be frequent and great on account of abrupt changes in 

 altitude, exposure, slope, soil, and moisture. The solution of the 

 problem is not obvious. 



VARIATION IN AlIOUNT OF FORAGE IN DIFFERENT YEARS. 



Areas within the National Forests generally are not subject to the 

 great variation in forage production which may occur on desert and 



