62 



CALCULATION OF THE POSSIBILITY [CH. vii 



of Class I trees will be sufficient or not for this purpose during 

 the first rotation. The total number of Class I trees that we 

 require as a working exploitable stock is the number of trees 

 becoming annually exploitable, — which we have already found 

 as the basis of our calculation of the yield, — multipUed by half 

 the number of years in the felling-cycle. This number then has 

 to be compared with the figure showing the number of Class I 

 trees in our table of enumeration, and any excess or deficit spread 

 out over a suitable number of years, and added to, or deducted 

 from, the original number of trees passing annually from 

 Class II to Class I. 



I 

 11 



III 



IV 



I 



II 

 III 



IV 



A B 



If the forest has not been in regular working up till now, we 

 have to change its constitution from A to B. 



During the first felling rotation the early fellings will depend 

 almost entirely on the accidental number of Class I trees that 

 happen to be standing on the ground, and the forest will not 

 come into full and regular production of an equal maximum 

 annual yield until the second felling-cycle, when the full suc- 

 cession of the necessary exploitable stock will be completely 

 constituted. 



It will be noted that the average age of the trees forming 

 the yield will be greater than the exploitable age by half the 

 number of years in the feUing-cycle. 



