82 DETERMINATION OF THE INCREMENT. 



I. Diameter Increment of the Future. 



This is estimated from the increment of the immediately 

 preceding period, taking into consideration how far the future 

 diameter increment may be affected by the method of treat- 

 ment, me /e especially the proposed degree of thinning. 



3. Area Increment. 



The increment in basal area is calculated from that of the 

 diameter. 



Let D be the mean diameter of the whole section, d the 

 diameter of the same section n years ago, then 



Basal increment ) _D z X7t_d 2 x TT 

 during n years j ~ ~~4. ~4 



The basal increment can be ascertained for a limited number 

 of years only, or for the several periods of the life of a tree. 

 An estimate of the future increment is based upon that of the 

 immediate past, taking into consideration the proposed treat- 

 ment, as in the case of the diameter increment. 



4. Volume Increment. 

 a. Of the Past. 



The past volume increment of a tree during a certain period 

 of years, n, is equal to the difference of volumes at the com- 

 mencement and end of the period. These volumes can be 

 ascertained by examining a series of sections at various heights 

 of the tree, or by basing the calculation upon measurements 

 made at the middle section, or by using form factors. 



i. DETERMINATION OF THE INCREMENT BY SECTIONS. 



If the increment of only a limited number of years, n, is 

 desired, it can be ascertained by means of the increment borer. 



