THE THEORY AND PRACTICE OF WORKING PLANS 5 



The growth per cent must always be translated into figures 

 of actual volume. For example: 



A spruce tree 28 inches in diameter at breast height, of 

 average height-growth, shows 8 rings in the last inch, bored at 

 breast height. The increment per cent according to Schneider's 

 formula is 



p = —^ — = 2 per cent. 

 ^ 28X8 ^ 



Assuming a stand of 2400 feet board measure per acre, the 

 volume increment (current annual) would be, if this were a 

 sample tree: 



2400 X 2 



100 

 Pressler's formula: 



= 48 board feet per acre per annum. 



F— 2; 200 



V-\-v n 



where p = the current annual increment per cent, F = the vol- 

 ume now, V = the volume ti years ago, and n = the number of rings 

 in the last inch of diameter. For example: 



A hemlock tree 18 inches in diameter at breast height, of 

 average height-growth, shows an average of twelve years to 

 grow the last inch in diameter. The volume of a hemlock 

 18 inches d.b.h. is 230 board feet; of a hemlock 17 inches 

 d.b.h. is 190 board feet.* The increment per cent accord- 

 ing to Pressler's formula is 



^ 2^0— iQO, 200 o 



p=-^ ^X =1-587 per cent. 



23o-fi9o 12 



Assuming a stand in which there were, on an average, .25 

 hemlock trees 18 inches d.b.h. per acre, with a corresponding 

 volume of 57.50 board feet per acre, the volume increment 

 (current annual) would be, if this were a sample tree: 



57.5X1.587 , J r ^ 



"^-^-^ ^— ^ = .91 board feet per acre per annum. 



100 



* Volumes based on U. S. Dept. of Agri., Bulletin 152, new series, Table 12. 



