108 

 and 



DETERMINATION OF THE INCREMENT. 



Increment in n years = v a+n 



V V ii 

 Tl 7 , / a+n * c 7 . _ 



^/vJ-ti. V n T^ I'/Y 



This method rests upon the assumption that the selected 

 yield table represents correctly the progressive increment of 

 the wood, of which the increment is to he ascertained. As 



-AGE 



Fig. 40. 



this is only approximately the case, the degree of accuracy of 

 the method depends 



(a) On the degree to which v a approaches V a , and 



(b) On the difference of ages, that is to say, the difference 



between a and a+n; the smaller this is, the more 



accurate will be the result. 



In following the above method, it is essential to measure the 

 volume on a "normal" sample plot, because only then can 

 the true quality class be ascertained by means of the volume. 

 If no fully stocked sample plot is available, that nearest to it 

 should be selected, and the proportion between the actual and 

 normal stocking ascertained. The actual volume must then 

 be augmented in the same proportion, before it is used for the 

 determination of the quality class. At the same time this 

 procedure is subject to errors, as it is not always easy to 

 determine correctly the proportion between the actual and 

 normal stocking. 



