144 UNITS OF MEASUREMENT FOR STANDING TIMBER 



121. The Tree as a Unit in Estimating. Volume Tables. The 



necessity for combined speed and accuracy to reduce the cost and 

 increase the reliability of timber estimates has led to the almost uni- 

 versal substitution of the tree unit for the log unit. Instead of entering 

 the size of each log separately, the dimensions of the entire tree are 

 noted. 



This requires that the volume of entire trees of the sizes tallied be 

 previously known. The sum of the volume of the logs which they con- 

 tain gives this information. A table, in which the average volume 

 of trees of given sizes is shown, is termed a volume table, in contrast 

 to a log rule or log table, which gives only the contents of single logs 

 and never that of entire trees. 



To avoid confusion in these terms, it should be noted that the stand- 

 ard definitions are: 



For a log-volume table — the term, Log Rule. 



For a tree-volume table — the term, Volume Table. 



The latter term should never be used by foresters to mean the 

 contents of logs, although the term log table may be used. The term 

 " volume table " always refers to the volume of trees, being substituted 

 for the longer descriptive term, Tree-volume Table. 



Timber cruisers were slow to see the advantage of thus tabulating 

 or summing up the total volumes of trees in systematic form. They 

 either adhered to the log basis, or in the instances when they used the 

 tree volume as a unit, merely calculated this for " average " trees by 

 mentally summing up the contents of the logs in individual trees, and 

 from the general knowledge thus obtained, assuming that trees in a 

 given stand averaged or " ran " a certain volume per tree. This method 

 was universally used in the South, where the Doyle rule readily lent 

 itself to quick mental computations of the contents of 16-foot logs 

 (subtract 4 inches from the diameter inside bark, and square the 

 remainder for board-foot contents of log, § 65). The total count of 

 trees, multiplied by the average contents per tree, gave the estimate. 



122. Volume Tables Based on Standard Tapers per Log. " Uni- 

 versal " Volume Tables. In the Pacific Northwest, the great height 

 of the trees and consequent large number of logs in each tree, and 

 the relatively few trees per acre, each with a large volume, soon brought 

 a realization of the need for substituting the tree unit for the log. The 

 difficulty of mentally computing the contents of trees varying so widely 

 in volume forced the use of the volume table, in which was recorded 

 the total volumes of trees of all sizes. These cruisers' volume tables, 

 of which several have been constructed, are, in most instances, based 

 on the principle of uniform taper per log, varying from 2 to 10 inches. 

 The contents of successive logs, as scaled by the accepted log rule, 



