164 



CONSTRUCTION OF STANDARD VOLUME TABLES 



(§ 26). The extreme range of volume caused by differences of form 

 alone for trees of the same height and D.B.H. is as much as 40 per cent. 

 Even the average volume of trees of the same ages or sites may differ 

 by more than 20 per cent. 



The volume of single trees follow the general law of averages. 

 Those which depart most widely from this law are few in number, 

 while a range of 5 per cent above or below the average would probably 

 include by far the larger number of trees in fairly uniform stands. 



When the exact volume of a specific tree is wanted it is unsafe to 

 assume that this tree is an average specimen. It must be measured 

 separately. But in estimating standing timber, the object sought is the 

 total volume of the stand, or the sum of all trees. If the average vol.- 

 ume of trees of each size class is correctly given in a volume table, 

 the cruiser can assume that every tree tallied is an average tree, and 

 the result or total will be the same as if the true volume of each sepa- 

 rate tree were measured. 



This averaging of the variable individual volumes of trees of each 

 class to obtain a reliable average volume is the principal service rendered 

 by volume tables. The timber cruiser stretches this same principle 

 much farther when he attempts to average the volumes of trees of totally 

 different diameters and heights, and the chances for error are much 

 greater, especially as this is usually a mental process or guess, while 

 the averaging of trees in a volume table is a calculation based on exact 

 measurements. 



The method of obtaining the average volume of trees for a given 

 size is as follows. Enter on a sheet, labeled with the diameter and height 

 class, the data for each tree, according to the illustration given below 

 for four trees. Place at top of sheet the tree class, e.g., 



