99 



year daring the period, in the compartments forming the revised first hlock, 50,583 

 cubic feet of material. During the first period, thinnings would be carried out in the 

 couiparlments of the other blocks until the end of the 30 years, when the compart- 

 ments m the second block would be taken in hand and dealt with in the same way. 



This method of calculating the yield is now, owing to the 

 difficulty of accurately estimating for long periods the future 

 growth, seldom used except in certain parts of Germany, 

 where, however, numerous improvements have been intro- 

 duced in the manner of verifying the possibility and iit 

 graduating the age-classes. These modifications are, however, 

 too complicated for adoption in this country, where indeed 

 the method is not generally suitable in present circumstances 

 owing to its complicated nature, its uncertain results, the 

 frequent revisions necessary, and above all the irregular 

 nature of most of the crops dealt with. 



Possibility: mixed method.— The volumetric method has been 

 generally replaced by a simplified form, known as the mixed 

 method, the essential feature of which is the two-fold 

 and simultaneous division of the exploitable age and the 

 area into corresponding portions. In other words, instead 

 of calculating the future growth of all the crops up to 

 the time of felling, the total area is divided into a num- 

 ber of equi-productive blocks, and the exploitable age into a 

 similar number of periods during which each block is in 

 its turn to be regenerated. The yield of that block which is 

 about to be taken in hand for regeneration is then calculated. 



Thus, in the example already taken, instead of calculating the future growth of 

 the crops in all the blocks, and then making transfers from one block to another so 

 as to secure an equal yield throughout, the forest area is partitioned off into four 

 blocks, each about 400 acres in extent or each of equi-productive resources. 

 Thus block I would contain the mature crops. 

 H „ „ large pole crops. 



III „ „ younger pole crops. 



IV „ „ young growth. 



In this partition the size of each block, where the elements of production vere not 

 uniform, would be enlarged or reduced, as the case might be, so that all might even- 

 tually yield about the same quantity of material. The yield of the first block only 

 wonld then be calculated. This would be done, as in the previous exainple by adding 

 to the material on the ground the estimated growth during half the length of the period 

 — in this case close on 15 years— and by dividing the total so obtained by 30, the nnm- 

 ber of years in the period. The future growth is obviously taken as the ayerHge srowtU 

 of the whole for Aa^/ the period only; because some of the crops would be exploitett 

 at the beginning and some at the end of the period. 



The trees in the block under regeneration would, as al- 

 ready stated, be generally removed gradually in several 

 successive fellings. The first, the preparatory or seed f ellmg, 

 would be made with the obiect of opening out the canopy so 



H 2 



