136 VALUATION OF THE GKOWING STOCK. 



AssuDiing now, that the wood has been injured by wind at a 

 previous period, so that no thinnings can be made before the 

 year 90, and that the growing stock would reaHse — 



At an age of 70 years . . . = 1,800 shillings, 

 ,, 80 „ . . . = 2,700 

 M 90 „ . . . =: 3,707 



then the expectation value of the wood under these rotations 

 would be as follows : — 

 For a rotation of 70 years — 



45/. _ 1,800-524 (1-02525-1) _,,„ , .,,. 

 <J"e -, '..,- '= 729 shiihngs. 



For a rotation of 80 years — 



i5r< - 2'700-524 (1-025--1) „.,„ , .,,. 



<J"e = , ' ,- = 83o shiihngs. 



l-02o-^' ^ 



For a rotation of 90 years — 



45/' - 3,707- 524 (1-025^^-1) ^^ i -ii- 

 (^e Ym^^ ^=868 shiihngs. 



For a rotation of 100 years — 



45/. _ 4,438+149x1-02510-524 (l-025"-l) ^,,, , .„. 

 O. ^^:^^555 = 801 shillings. 



It will be observed, that the maximum expectation value of 

 the growing stock is, in this case, obtained under a rotation 

 of 90 years. 



iii. TuE Age of the AVuod. 

 The expectation value of the growing stock rises (given a 

 fixed rotation) with the age of the wood, but not in exact 

 proportion. If the thinnings are made after regular intervals, 

 say every 10 years, it generally happens, that, immediately 

 before making thinnings, the expectation value is slightly 

 higher, than immediately after the thinning has been made. 

 For instance, if a thinning is made in the year 60, the 

 ex^Dectation value of the growing stock for the year 59 will 

 probably be higher than for the vear 61. 



