SIZE OF THE AGE CLASSES. 209 



Or, the first cutting may be made in the year r — ~ and 



A 



the last in the year /• + - , so that the mean final age comes 

 'A 



to r years. 



In the present chapter the latter is assumed. 



d. The Selection Sysiem. 



Strictly speaking, the annual coupe is equal to the total 

 area of the forest. For convenience sake, however, the cuttings 

 of each year are restricted to a portion of the area, so that it 

 takes a number of years to go round the forest, and before 

 cuttings are again made on the same area. If that number 

 is /, then — 



Annual cutting area = y. 



Example. — In the beech forests of Buckinghamshire, which 

 are worked under the selection system, it is usual to go round 

 once in seven years ; in that case the annual cutting area 



A 



would be equal to — . In other cases, as in the Indian sal 



and teak forests, / is longer, generally from 15 to 40 years. 



2. Size of the Age Classes. 

 In forests of some extent, which are worked under a high 

 rotation, and especially those regenerated naturally, it is, as a 

 rule, impracticable to separate the annual cutting areas, so 

 that a regular series of age gradations, differing by one year 

 in age throughout, exists. In these cases, it is necessary to be 

 satisfied with larger groups, that is to say, to join a number 

 of age gradations into an "age class." The normal size of 

 such an age class depends on the area of the annual coupe 

 and the number of such coupes thrown together. If a class 

 contains n gradations, its area would be = n X c. The number 



of age classes = — is variable. 

 u 



