236 



THE NORMAL GROWING STOCK. 



rotation in each case, the following results are obtained for 

 spring : 



The above example shows that the normal growing stock, 

 calculated with the mean annual increment, is larger than that 

 calculated from a yield table up to the age of 50 years ; 

 between 50 and 60 years the two are equal, and after that the 

 latter is greater than the former. Under these circumstances 

 it is evident that, except for a rotation from 50 to 60 years, a 

 considerable error is committed in the above case by calcu- 

 lating the normal growing stock with the mean annual increment 

 of the final crop. 



I. Shelter-wood Compartment System. 



The normal growing stock is the same as for the clear 

 cutting system, provided the regeneration cuttings are so 

 arranged that one half are made before the year r, and the 

 other half after it. Strictly speaking, this is only correct if the 

 timber in the regeneration class is removed in annually equal 

 quantities, and if regeneration takes place in the middle of the 

 period. In reality this does not occur, but the deviations 

 compensate each other in the long run ; anyhow a more 

 accurate determination is practically impossible. 



