28 



Forest Mensuration 



PARAGRAPH XLIV. 



SELECTION OF SAMPLE TREES. 



Sample trees are selected either irregularly or after a regular plan. In 

 the latter case, it is best to distribute them equally among the diameter 

 classes composing the forest (Draudt-Urich method and Robert Hartig 

 method), instead of selecting sample trees of average diameter. 



It is more important that the sample trees should have proper average 

 class-form height (and average defects) than that they should have exact 

 average class-diameters. 



PARAGRAPH XLV. 



DRAUDT-URICH METHOD. 



The Draudt-Urich method is in common use abroad for measuring 

 the forest. The trees of the forest are divided into a number of classes 

 (usually five). Each class contains an equal number of trees, class i 

 containing the largest and class 5 the smallest trees. In each class an 

 equal number of sample trees, having about the average diameter of the 

 class, are felled and worked up into logs, cordwood, ties, poles, etc. The 

 form height of all sample trees is obtained as the quotient of their volume 

 (in any unit or mixture of units) divided by their sectional area. Mul- 

 tiplying the sectional area of the forest with this form height, the exact 

 volume of the entire forest and its composition (logs, poles, cords, etc.) 

 are given by one operation. 



Sample trees of the average diameter of a class are found by dividing 

 the sectional area of the entire class by the number of trees per class. It 

 is wrong to find the average diameter by dividing the sum total of the 

 diameters by the number of trees. 



