232 THE NORMAL GROWING STOCK. 



(2) Because several methods base the calculation of the 

 yield upon the difference between the normal and 

 real growing stock. 



The amount of the normal growing stock is proportional to 

 the length of the rotation ; the higher the latter, the greater 

 the former. 



In calculating the normal growing stock only the principal 

 part of the woods which give the final yield are taken into 

 account, because, as previously explained, the determination of 

 a sustained yield is, in the first place, based upon the final 

 .yield. 



The normal growing stock can be looked at from the 

 volumetric or the financial point of view. 



1. Calculation of the Normal Growing Stock as regards 

 its Volume. 



The calculation can be made either by means of yield tables 

 or the mean annual increment. The former is the only correct 

 method, but the latter must be explained, as it is used by 

 several methods of calculating the yield. The calculation 

 differs for the several methods of treatment. 



a. Clear Cutting in High Forest. 



(1) Calculation from Yield Tables. If a yield table is 

 available for a forest, which gives the final yields from year to 

 year, the normal growing stock is equal to the sum of all 

 yields in that table from the year 1 to the year r (the rotation) ; 

 that sum would represent the normal growing stock of r units 

 of area, and for the season when the annual growth has been 

 completed, but before the annual cuttings are made; in Europe 

 this would be autumn. 



If the yield table, and this is generally the cse, gives the 

 volumes only from period to period, say for every n years, then 

 the approximate amount of the normal growing stock can 

 be calculated (according to Pressler), by assuming that the 



