184 THE INCREMENT. 



(5) Whenever the object of management consists in the 

 realization of the greatest return of volume, the rota- 

 tion must coincide with the year in which the mean 

 annual increment culminates. The time when the 

 maximum for final yield only occurs, differs from that 

 for final plus intermediate yields ; the difference may 

 amount to 10 and, even 20 years, especially if heavy 

 thinnings are made at an early period. 



2. Quantity Increment Per cent. 



So far the increment has been expressed in actual volume. 

 In addition, it is useful to ascertain the proportion which 

 exists between the total volume of a tree or wood at a certain 

 age, and the increment laid on during the year before or the 

 following year. In order to express this proportion indepen- 

 dently of the actual volume, it is usual to give it in per cents., 

 and to call the proportion the " increment per cent." ; by this 

 is, therefore, understood the current annual increment which is 

 laid on by every 100 units of volume. 



; The increment per cent, is used, sometimes to calculate from 

 the present volume the increment which is likely to be laid on 

 in the immediate future, but is chiefly employed for the purpose 

 of testing the activity of the capital invested in forestry. 



Let the volume of a tree or wood at a certain age = v, 



,, the same tree or wood one year later = F; 



then the increment of one year i = V v. 



Let further the increment per cent, of the volume = p v , 

 then 



and 



p c = Zn?xlOO = -xlOO. 



v v 



The same expression is obtained by considering V as the 

 accumulated value of v, produced by v working with interest 

 for one year, in other words : 



