94 PRACTICAL FOREST MANAGEMENT. 



therefore requires 30 years for a tree to pass from a diameter of 18* 

 to one of 24". Now Rs. 7*5 the value of a II class tree 

 accumulated at 4 per cent, compound interest for 30 years 

 amounts to Us. 24*325 or Rs. 1*825 in excess of the current value 

 of the lowest diameter class of a I class tree, viz., Rs. 22 '5 show- 

 ing that the rate of compound interest received is slightly less 

 than 4 per cent. As however trees of not leas than 24" are 

 required in order to fulfil the objects of management (the provision 

 of B. G. railway sleepers) an exploitable diameter of 24" 

 is perfectly justified. But Rs. 7*5 is the value of an average II 

 class tree and not of an 18" tree, the average age of this 

 class should therefore be taken and not the age of entry into this 

 class. The average age of the II class tree is 92 years and that of 

 I class 24" to 26" is 115, so that the average time required 

 for a tree to increase in value from Rs. 7*5 to Rs. 22'5 is 23 years. 

 Now Rs. 7*5 accumulated at 4 per cent, compound interest for 23 

 years amounts to Rs. 18*485, so that the retention of trees to 

 24" diameter is fully justified on financial grounds alone. 



" Continuing the investigation further it will be seen that 

 21 years are required for an average I class tree 24" to 26" 

 diameter to grow into an average tree of the next higher diameter 

 elass 27" to 29* but Rs. 22'5 accumulated at 4 per cent, compound 

 interest for 21 years amounts to Rs. 50'273, whereas the 

 latter diameter class is only worth Rs. 30. Hence there is a loss 

 of Rs. 20 per tree in retaining trees after they have reached 

 the diameter class 24" to 26". 



" Now a diameter of 26" corresponds to a rotation of 120 

 years. This rotation will produce a chir of just about 24", Kail 

 of 29", a spruce of 27", and silver fir of 27" ; so that with the 

 exception of the last species this rotation is suitable both for 

 deodar and its associated species. With regard to the silver fir 

 it is supposed that under regular management the growth now 

 shown will be accelerated, in any case its rotation must conform 



