60 



CONTENTS OF STANDING TREES. 

 Estimate by the Eye. 



Persons who have constant practice in measuring logs and trees 

 are able to estimate the contents of standing trees by a mere super- 

 ficial inspection. Skilled timber cruisers attain an astonishing 

 degree of accuracy in such estimates, but this estimating of the 

 contents of trees at a glance is possible only to one with special 

 training. The inexperienced cruiser or one who is estimating an 

 unfamiliar species must calculate the contents of standing trees 

 from measured or estimated diameters and by the use of a log rule. 

 It is necessary first to determine the lengths of the logs; then the 

 diameter inside the bark at the top of each log. The scale. of each 

 log is obtained from a log rule and the results for the different logs 

 added together for the total scale of the tree. This method in- 

 volves the ability to estimate diameters at different points up the 

 tree and involves also a knowledge of the thickness of the bark, 

 which varies at different points. 



An often-used method is to estimate the length of the merchant- 

 able portion of the tree, then estimate its top and base diameters, 

 average these diameters, and determine the contents by the Doyle 

 Rule. If the length of the merchantable portion of a tree is 40 feet, 

 the top diameter 6 inches, and the base diameter 14 inches, the 

 average diameter would be assumed to be 10 inches, and the volume 

 of the log would be, by the Doyle Rule, 90 board feet. 



A number of rules of thumb are in existence for estimating the 

 number of board feet in standing trees. The following is a good 

 illustration : 



Subtract 60 from the square of the estimated diameter at the 

 middle of the merchantable length of the tree, multiply by 0.8, 

 and the result is the contents in board feet of the average log in the 

 tree; multiply by the number of 16-foot logs for the total scale. 



For example, if the estimated merchantable length is 50 feet 

 and the estimated middle diameter is 10 inches, there would be a 

 subtraction of the arbitrary 60 from 100, the square of the diameter, 

 with a remainder of 40. This multiplied by 0.8 gives 32 feet for , 

 the average log, and for the three 16-foot logs in the 50 feet of 

 merchantable length gives 96 board feet as the total contents. 



