90 



DETERMINATION OF THE INCREMENT. 



ii. DETERMINATION OF INCREMENT BY THE MIDDLE SECTION. 



If somewhat less accurate results suffice, the volumes can be 



ascertained by multiplying the basal area in the middle by the 



height. Let V be the volume of the tree at the present time, 



v that n years ago, H and h the corresponding heights, figure 33, 



and S and s the corresponding basal areas at ~- and -^-, then 

 I=V-v = SxH-sxh. 



TT 



The height and basal area at - can easily be measured; 



Fig. 33. 



