AGE OF WOODS. 75 



to avoid exceptionally thick trees, as such trees may represent 

 former advance growth. 



As whole woods are rarely established in one year, owing to 

 failures and subsequent repairing, or, in the case of natural 

 regenerations, owing to two or more seed years being necessary 

 to the complete stocking of the area, it is generally desirable 

 to examine several trees and take the mean. 



1). Uneven-aged Woods. 



In many cases woods are less even-aged than has been 

 indicated above. The differences in the age of the several 

 component parts of the wood may be very considerable, as 

 regeneration may have extended over a long period. In such 

 cases the mean age must be ascertained. 



By the " mean age " of an uneven-aged wood is understood 

 that period which an even- aged wood requires to produce the 

 same volume as the uneven-aged wood. 



Let 



a lt a> 2 , %, . . . be the ages of the several age classes ; 

 v i> v z> v s> ... be the volumes of the several age classes ; 

 7, the mean annual increment of an even-aged wood of the 



same volume as the uneven-aged one ; 

 A, the mean age, or the age of an even-aged wood of the same 



volume as the uneven-aged one ; 



Then, according to the above definition, the following 

 equation holds good : 



v l +v 2 +v s + . . . = IxA, 

 and 



m 



As the even-aged and uneven-aged woods are assumed to 

 have the same volume, it follows that I must be equal to the 

 sum of the mean increments of the several age classes of the 

 uneven-aged wood, that is to say : 



a+aj... 



0? d,, 



