316 DETERMINATION AND REGULATION OF THE YIELD. 



Whereas the method by area estabhbhes the normal state of 

 the forest withm one rotation, the method b}' volume takes 

 several rotations to accomplish this. 



As regards its financial aspect, it stands on about the same 

 footing as the method by area. 



3. TJte Method nf Periods hjj Area and Vohuiu: condnned. 



The woods of a forest are so allotted to the several periods 

 of a rotation, that each contains the same area and yields the 

 same, or approximatel}^ the same, volume. 



The equalisation of the periodic areas and returns is effected, 

 either by adding columns for the volume to the general 

 working plan used for the method b}- area, or by adding 

 columns showing the reduced areas to the general working 

 plan used for the method by volume (see page 389). Shiftings 

 are made, until l)0th area and yield are the same, or approxi- 

 mately the same, in each period. 



It will easily be understood, that such an equalisation is a 

 difficult operation, especially in a very abnormal forest; hence, 

 more than an approximate equalisation cannot be attempted. 



The method shows some of the advantages and disadvan- 

 tages of the two previous methods, of which it is a combination. 

 Its principal disadvantage is, that a suitable grouping of age 

 classes is still more difficult than in the case of each of the two 

 component methods. 



In practice, various modifications of the above three methods 

 have been evolved, which sometimes partake more of one and 

 sometimes more of another of the methods. 



C. Regulation of the Yield according to Increment 

 and Growing Stock. 



The methods coming under this heading calculate the yield 

 by means of a formula, which is leased on the increment laid 

 on and any difference, which may exist between the real and 



