SIZE OF THE AGE CLASSES. 215 



A 



Annual cutting area = - . 



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 



would he equal to - . 



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 thrown together. If a class contains n gradations^ its 



* 



area would be = n x c. The number of age classes = - is 



variable. 



Another way is to fix the number of age classes ; in that 

 case n is variable, but this procedure is not to be recommended, 

 as it is likely to lead to confusion. 



It is usual to take for n a round number, say 10, 20, or 

 even 30; in coppice woods n is usually taken as =5. The age 

 classes are numbered. It is best to call the youngest I., the 

 next youngest II., and so on; for instance, if n = 20 



First age class I., contains all woods up to 20 years old. 

 Second ,, II., ,, ,, from 21 to 40 years old. 



Third III., 41 to 60 



and so on. 



In this way the number of the age class indicates directly 

 its age. The reverse method, of calling the oldest age class I., 

 the next oldest II., etc., is less desirable, but unfortunately 

 it has been largely adopted. An effort should be made to alter 



