Method of Cruising Timber. 381 



ing as before the character of the timber as he drives along se- 

 lects another spot where the size and occurrence of the timber 

 appears to be typical. Here in the same manner he measures 

 about a score more of trees. This is repeated as many times as 

 his convenience will allow. 



When he returns to his office the timberman has measurements 

 of the diameter of a large number of trees and of the distance 

 between them in the order in which the measurements were 

 taken. The diameter of the average tree among which he has 

 measured is then determined. Being of a scientific turn of mind, 

 this timberman recognizes the axiom that the volumes of trees 

 vary more nearly as the squares of their diameters than as their 

 diameters. He determines the diameter of the average tree there- 

 fore in the customary manner by computing first the average 

 basal area of all the trees and from this the corresponding diam- 

 eter. The volume of the average tree is then computed either 

 from a volume table or from a log rule, making allowances for 

 height, taper, and thickness of bark. 



The next step is to determine the average number of trees per 

 acre. The distances between the measured trees are totalled and 

 this total is divided by the number of measured distances. The 

 result gives the average distance, measured in feet, that each tree 

 is apart from its neighbor. This average distance is then squared 

 to obtain the average area or ground space in square feet that each 

 tree is allotted in the forest. This average area is then divided 

 into 43,560, the number of square feet in an acre, to determine the 

 average number of trees per acre. 



The rest is simple. The volume of the average tree is multi- 

 plied by the average number of trees per acre and the result 

 is the volume of timber in board feet on an average acre. The 

 product of this average volume per acre and the acreage of the 

 claim gives the total volume or cruise on the tract of land under 

 consideration. 



This method of course has many drawbacks which tend to give 

 inaccurate results. An error in selecting an area where the den- 

 sity of the stand and the size of trees is not representative of the 

 whole tract will result in an estimate either too high or too low. 

 No data for the preparation of a map can be taken by this method 

 and the estimate can not be separated by species. It should be 



