24 



DETERMININa VOLUME BY SAMPLE TREES OF DIAMETER CLASSES. 



More accurate results in ascertaining the growing stock of a forest 

 may be obtained by arranging the trees of each species in diameter 

 classes and then finding and measuring a sample tree of each class. 

 The calculation to determine the basal area and, hence, the diameter of 

 the sample tree of a diameter class, the selection of the sample tree in 

 the forest and its measuring -and the calculation of the volume of the 

 diameter class are performed in the same way as described above. 

 Each diameter class is to comprise trees differing not more than 4 

 inches in diameter at breast height. The oak of our hard-wood grove, 

 then, would be divided into five diameter classes. The first diameter 

 class would contain trees from 8 to 11 inches in diameter, inclusive; the 

 second, trees from 12 to 15 inches, inclusive; the third, trees from 16 to 

 19 inches, inclusive; the fourth, trees from 20 to 23 inches, inclusive; 

 and the fifth, trees from 24 to 25 inches, inclusive. 



The first diameter class would then contain : 



No. of 



trees. 



Sinclies in diameter ' 23 



9inclies in diameter i 76 



10 inches in diameter ; j 87 



11 inches in diameter 172 



Total 358 



Basal area. 



Square feet. 



8.03 



33.58 



47.45 



113. 52 



202. 58 



The basal area of this diameter class, 202.58 square feet divided by 358, 

 the number of trees it contains, gives the basal area of its sample tree as 

 0.56 square foot, which corresponds to a diameter of 10.1 inches. Two 

 sample trees of 10.1 inches selected accordingly in the forest among the 

 oaks had in the average a volume of 16.8 cubic feet and scaled 60 feet 

 B. M. Multiplying 16.8 and 60 each by 358 (number of trees in the 

 class), we obtain 6,014.4 cubic feet and 21,480 feet B. M., which is the 

 volume of the first diameter class in cubic and superficial feet respec- 

 tively. The same process is repeated for the other diameter classes 

 and species, selecting and measuring a smaller or larger number of 

 sample trees as the diameter class contains a smaller or larger total 

 number of trees. The final addition gives the volume of the stand. The 

 accompanying table (Form Xo. 4) illustrates in detail the manner of 

 recording and computing the growing stock of our hard-wood grove by 

 arranging each species in diameter classes. 



