82 REPORT OF THE 



The Group Method. 



By this method the trees of a stand are divided into several groups, and sample 

 trees are felled for each group. From these sample trees the volumes of the separate 

 groups are calculated. These volumes added together give the volume of the whole 

 stand. 



The number of groups is dependent upon the accuracy desired. As for the whole 

 stand in the preceding method, so for the group in this method, the sample tree 

 should represent the mean cross area and the mean height and form factor of the 

 group. The larger the number of groups, the more nearly will this condition be 

 satisfied, but the more laborious will be the calculation, since each group must 

 be treated by itself. 



If in measuring a stand great intervals have been made between the diameter 

 classes, in accurate work each diameter class may be considered a group. The 

 calculation of the diameter of the sample tree is then saved, since this possesses 

 the mean diameter of the class into which it falls. 



If 7'i, v-i, Vs, etc., be the volumes of the individual groups, then the volume of 

 the stand, V = Vi + t'i + z'^ -\ 



As has been shown, the volume of each group may be found by multiplying the 

 volume of the sample tree of the group by the number of trees. 



V -^ V X n, 

 or by the formula 



a 

 As has been pointed out, the volume of a stand may be obtained by the formula 



Now, \{^=^=.^ = C 

 (ii a-i rts 



Then V=-C{v, + v,+ v,). 



That is, if this condition were satisfied it would not be necessary to calculate the 

 volume of each sample tree and group separately, but the sample trees could all be 

 worked up together. This would simplify the calculation very much. The volume 

 of a stand would then be obtained by multiplying the total volume of the sample 

 wood by the common factor C. 



This condition is not satisfied, however, by the Group Method but is well reached, 

 as will be seen, by the Draudt and Urich methods. 



