328 DETERMINATION OF THE YIELD. 



series of years, plus or minus the quota of growing 



stock determined under (b). 



It is obvious that these objects can only be realized by a 

 complicated procedure, and even then only approximately, 

 because changes in one direction disturb the balance in 

 another. 



2. Practical Application of the Method. 



(a) The first step is to allot, by means of the table of age 

 classes, all woods to the several periods and to equalize 

 the areas by suitable shiftings, as indicated under the 

 method of periods by area ; care being taken to allot 

 the woods with due consideration to sylvicultural 

 requirements, and a proper distribution of age classes, 

 as far as this is practicable. 



(&) The real increment is placed equal to the real final mean 

 increment, for which purpose it is necessar}^ to deter- 

 mine the final age of each wood (which may differ from 

 the normal final age), and its probable volume at that 

 age ; the latter divided by the former gives the mean 

 annual increment. In order to avoid having to cal- 

 culate the increment year by year, it is generally 

 calculated for a number of years, which may be called 

 a. If an abnormal wood is cut over during the a 

 years at an age differing from the normal, and a 

 normal wood grows up in its place, the increment must 

 be calculated separately for each part of a years. 



(c) The normal and real growing stocks are calculated as 

 for the Austrian method ; the former is placed 



Ixr 



, where I represents the normal final mean 



a 



increment ; the latter is obtained by multiplying the 

 real final mean increment of each wood by its age. 

 The difference between the real and normal growing 

 stock is removed as may be approved by the owner, 

 say, in equal amounts in the course of a years. 



