THE THEORY AND PRACTICE OF WORKING PLANS 103 



403.08 + ( 5.478 X- 



r 



2 



_ 403.08 + (5.478X40) 

 80 



_403.o8 + 2i9.i2 

 80 



622.20 

 =-— r — = 1-11^ board feet of hemlock per acre 

 80 



or, for the 1730 acres in this tj-pe, =13,456 board feet of 

 hemlock. 



Example of Variation II. — It is desired to determine the 

 cut of hemlock in the slope t\^e of Catskill forest, illustrated 

 by the stand and stock tables quoted above from Bulletin ii 

 of the N. Y. State Conservation Commission.* The number 

 of years required to grow from one diameter class to the next 

 has been determined by increment borings and the current annual 

 increment per cent has been worked out by Pressler's formula 

 (see data in example under Method No. 4). These show that 

 trees of 20 inches d.b.h. and over have a c.a.i. of less than i 

 per cent and so may be regarded as surplus stock (z in method 

 No. 4). The d.b.h. limit chosen is 12 inches. This leaves a 

 merchantable stand of trees from 12 to 20 inches, d.b.h., as the 

 basis of computation. It is simpler to group these in 3-inch 

 classes, as follows: 17 to 19 inches equals 18-inch class; 14 to 

 16-inch equals 15-inch class; 11 to 13-inch equals 12-inch 

 class. To this must be added the class immediately below the 

 diameter limit class, that is, 8 to 10 inches equals 9-inch class. 

 From table 9 of the aforesaid Bulletin 11 are taken the volumes 

 of 18, 15, 12, and 9-inch trees, respectively. The years required 



* Bulletin ii, "Forest Survey of a Parcel of State Land," Albany, N. Y., 

 1915, Tables 4 and 5. See pages 47 and 48. 



