STAND BY MEANS OF FELLED TREES 71 



8. Determine the volume of each in cubic feet bj^ Smahan's method, 



using 10-foot sections. 



9. In order to correct any error resulting from a difference in the diameters 



of the sample trees and that of the average tree as calculated deter- 

 mine the contents of the average plot by the formula : 



vXB 

 ^ ~ b ' 



in which l' = the volume of the average acre; 

 /' = average volume of test trees; 

 /?= total basal area of the plot; 

 6 = average basal area of the test trees. 



Reduce to acre terms. 

 10. Determine the contents of the entire stand. (40 acres assumed.) 



Illustration II. — The Arbitrary Group Method. 



Principle. — The principle of the method is to group all the trees measured on 

 the plot into arbitrary D.B.H. classes. Each group is then treated in 

 exactly the same manner as were all the trees in the Mean Sample Tree 

 Method. The chief difference between this and all other methods in 

 which the trees are grouped is in the manner of grouping and the number 

 of test trees to be cut. 



Directions: 



A. Parties ami Equipment a.s in Illustration I. 



B. Method of Procedure. 



1. Use the same area for the tract, the same plot and the same diameter 



measurements of the standing trees as in Illustration I. 



Note. — The same plot is here suggested for each illustration given in order to give the 

 student a thorough basis for comparing the different methods. Sometimes the plots can be 

 located in timber which will be cut before the completion of the course in mensuration. In 

 that case all the trees can be carefully measured, and the contents can be computed accu- 

 rately from the felled trees and then compared with the results obtained by the different 

 sample plot methods. 



2. Group the diameter measurements into three or four groups, so that 



each group or diameter class does not, so far as possible, vary by 

 more than 4 inches. 



3. Proceed with each group (diameter class) just exactly as was done for 



all the trees in Illustration I. Record sample tree measurements on 

 Form 2 A. 



4. Arrange all data in tabular form similar to that used in Illustration I. 



5. From these measurements now determine the cubic foot contents of 

 the 40-acre tract. 



