182 THE INCREMENT. 



overtopped and suppressed ; these form ordinarily the material 

 of which the thinnings consist. 



In fully stocked woods, especially in those treated as high 

 forest, a distinction must be made between the dominant and 

 suppressed trees ; the former may be called the major or 

 primary part of the growing stock, and the latter the minor or 

 secondary part. Not only the latter, but also a considerable 

 portion of the former, will be removed in the thinnings, in the 

 same degree as, with the advancing age of the wood, the.y lose 

 their dominant character and join the secondary part of the 

 growing stock. 



The progress of the increment in whole woods has, by no- 

 means been determined for all important species, though much 

 material bearing on this question has been collected of late 

 years on the continent of Europe. In India matters are still 

 more backward. So much, however, has been determined, 

 that both the current and mean annual increment culminate 

 much earlier than had been supposed. 



The yield tables for some of the more important European 

 species justify the following conclusions : 



(1) The current annual increment rises rapidly after the 



first youth is passed, and reaches its maximum about 

 the time when the height growth culminates ; it then 

 falls, and reaches zero at the death of the wood. 



(2) The mean annual increment keeps below the current 



annual increment, until the two become equal; after 

 that period the mean annual increment is greater than 

 the current annual increment. 



(3) The mean annual increment reaches its maximum at 



the precise moment when it is equal to the current 

 annual increment. Gustav Heyer has proved this in 

 the following manner : 



Let c it c z , c 3 , . . . c n , c n+1 , be the current annual increments 

 of successive years ; m lt m 2 , ra 3 , . . . m n ,' m n+1 , the mean annual 

 increments for the same years ; then the current annual incre- 

 ment of the year (n + 1) is represented by 



