78 



REPORT OF THE 



How to Find tl)e Volctme of a Forest h% Felling 3ample 



Trees. 



Mean Sample Tree Method. 



The trees of the forest are measured as already described. The basal areas of 

 the cross sections, breast height, are calculated from the diameters. Then, by 

 adding these basal areas the total basal area is obtained, and by dividing the total 

 basal area of any species by the number of trees of that species the basal area 

 of the average sample tree of the species is obtained. 



Let V = volume of the stand. 



V = volume of the average sample tree. 



A = total basal area. 



n = basal area of sample tree. 



;/, == number of trees with cross area (T,. 



71^ = number of trees with cross area (Tj. 



;/, ^ number of trees with cross area do. 



Then a = 



total number of trees. 



a, 7/| + ^2 "2 + ^3 «S + 



A 

 u 



From this basal area of the average sample tree is then calculated the corre- 

 sponding diameter, and from the height measurements is ascertained the average 

 height corresponding to this diameter. 



A thrifty tree of the species having this diameter and height is selected in the 

 forest. It is felled and its volume measured. In order to obtain a volume inde- 

 pendent of the individual irregularities, several of such specimens are felled and 

 measured. The average cubic contents of these represents the volume of the mean 

 sample tree. This volume, when multiplied by the number of trees, gives the 



volume of the stand. 



V =v Y, n 



Since it has been shown that 



A . A 



a = ■ — ; then, n = — 

 ;/ a 



Substituting this value for ii in the formula above, and, 



A 



V =v 



a 



The following table shows a convenient form for keeping the record : 



