CLASSIFICATION AND AVERAGING OF TREE VOLUMES 163 



computed. The measurement of merchantable volume of limbs and 

 branches is discussed in § 146. 



For obtaining the total volume of the tree bole exclusive of branches 

 by regarding the bole as a complete paraboloid, the so-called Schiffel's 

 Formula may be applied. For this purpose the area of the cross 

 section at D.B.H., and one at one-half height above stump is obtained 

 and applied, thus: 



F=(.16fl+.66 6J)A (§177). 



Volume of Bark. The volume of the tree may be computed from 

 D.O.B. to give total cubic contents with bark. It is then computed, 

 if necessary, from the D.I.B., to give the peeled contents or wood 

 without bark. The volume of bark is obtained by subtraction of the 

 second from the first result. 



Volume tables give the volume with bark, or without bark, accord- 

 ing to the use to which wood is put and the form in which it is sold. 

 When the peeled volumes are given, the per cent of bark in terms of 

 peeled volume may be shown for each diameter. 



137. Classification and Averaging of Tree Volumes According to 

 Diameter and Height Classes. 1. The separate sheets are now sorted 

 first into diameter classes (§ 127). 



2. The height classes, for tables giving total cubic volume, are based 

 on total height of tree. Whether 10-foot, or 5-foot classes are used 

 depends on the total height of the species. For second-growth hard- 

 woods or small timber, 5-foot classes are preferred, while in the extremely 

 tall timber of the West Coast, 20-foot classes are sometimes sufficient. 

 For either standard, trees are placed nearest their actual height. The 

 trees of each diameter class are now sorted into their respective height 

 classes. The trees in each separate diameter and height class are then 

 checked to see that no mistakes of classification have been made. 



3. The average volume is found for the trees of each separate group 

 or class comprising all trees falling in the same diameter and height 



If trees having the same diameter and height had similar forms, 

 the volumes of all trees in any one diameter and height class would 

 be equal, except for the differences due to the fact that the actual 

 diameter, or height, though falling within the size limits required, may 

 be larger or smaller than the exact standard size of the class. 



But variation in the form of the bole is a third factor which causes 

 considerable variation in volume for trees of the same total height 

 and diameter (§ 166). Trees whose form is full, lying between the 

 paraboloid and the cylinder, have a correspondingly greater volume 

 than trees with a form lying between the paraboloid and cone, or neiloid 



