30 



HARTIO'S METHOD. 



In this method tbe groups are so formed that the component trees 

 Aggregate equal basal areas. 



The procedure is as follows : 



First decide what number of sample trees () or of groups of 

 trees (G) we require, and theu determine the aggregate basal area 

 to be included in each group (this area = TT or -77). Now form 

 the groups, beginning with the smallest class of trees. Next the 

 girths of the several sample trees are either fixed approximately 

 by inspection, or rigorously determined by means of the formula 



a ~- . Each sample stem is then measured by itself, and the 

 n 



contents of the corresponding group ascertained with the help of 

 the formula C = c . Or the contents of each sample tree may 



be considered as the contents of an imaginary cylinder of the 

 same base as the tree, and the corresponding height of the cylinder 

 obtained from the formula li ^ the total contents of the crop 



OJ 



being the product of the total basal area oE the crop multiplied by 

 the mean of all the cylindrical heights thus obtained. 



In this method the larger stems obviously compose, number for 

 number, more groups than the smaller ones, and the sample trees, 

 although of course samples of the corresponding group, are not 

 samples of the crop considered as a whole. The contents or yield 

 in different classes of produce of the sample trees cannot hence be 

 worked up together in one place, and the main advantage afforded 

 by Draudt's method is thereby lost. Comparing the two methods, 

 Hartig's may be employed when as accurate as possible an estimate v 

 of the contents of the crop is required with the help of only a few 

 sample trees, whereas Draudt's should be adopted when it is possi- 

 ble to fell a larger number of sample trees and an estimate of the 

 yield in different classes of produce is required. 



EXAMPLE OP THE THREE METHODS. 



To render the preceding explanations clear, we proceed to show 

 below, by means of a comparative .parallel statement, how to use 

 the three methods of valuation just described. We take the case 

 of a 1'7-acre sample plot of beech. 



