FOREST MENSURATION. 173 



It Tvill be noticed that these areas are taken at the 

 middle of a four-foot section; so multiplying the sum by 

 four, the volume of the trunk, from the ground to a height 

 of 28 feet, is found to be 6.1092 cubic feet. Treating 

 the top length of twelve feet as a cone, its volume is one- 

 third times the basal area into the height — .0341 X 12 -^ 3 = 

 .1364 cubic feet — ^which added to the volume of the 

 lower portion gives total volume of the tree 6.2456 cubic 

 feet. 



MEASUREMENT OF GROWING STOCK. 



The Growing Stock of a Forest, or Volume of Standing 

 Timber, is equal to the sum of the volumes of all the trees. 

 Where the tract is small caliper all the trees, or if the 

 tract is large caliper all the trees on a small sample area 

 selected as typical of the whole. If each species is in 

 uniform stand, separation into species classes will be 

 sufficient, but where much difference exists between in- 

 dividuals of the same species, due to conditions of growth, 

 diameter, and height, classes in each species should be 

 formed, and the volume of each class computed by itself. 

 From the diameters obtained by .calipering at breast- 

 height the average basal area is determined in each class, 

 and trees of corresponding diameters in each class are 

 felled and measured accurately. The volume of a sample 

 tree, or the mean volume of several sample trees, times the 

 number of trees, gives the volume of that class, and the 

 sum of the volumes of the different classes is the total 

 volume of timber on the tract. The more sample trees 

 that are measured, the more accurate will be the results, 

 as trees vary so much in shape that quite different vol- 

 umes may be obtained for two trees of the same diame- 

 ter and height. The following example illustrates this 

 method: 



