Normal and Actual Forest, Etc. 



161 



The follomng case illustrates this : 



White pine in New York State has been reported to grow as 

 follows : 



Yield at 60 yrs. =45 M. ft.; D.B.H. = 12 inches (merchantable). 



Yield at 100 yrs. = 70 M. ft.; D.B.H. = 20 inches. 



Using these figures with our triangle diagram we have : Growing 



stock, average per acre, -y = -^ — =35 M. ft. If the period of 



return is twenty years and the rotation 100 years then the cut 



takes at each return : 



2C 

 Cut = T7^ X 20 = 40% of the growing stock. 



But since the 12-inch material at 60 years is merchantable, the 

 total merchantable here makes 64 per cent, so that we have the 

 growing stock, just before cutting a lot made up of three parts: 



1 — the 40% merchantable to be removed in the cut; 



2 — the 24% now merchantable but left to grow; 



3 — the 36% of material smaller than 12 inches. 

 This may be illustrated by the following diagram : 



sfe A^.'.l 2 3 4 5 6 7 e 910 11 12 13 1415 15 27 1819 20 



In this diagram lot No. 1 is assimied ready for cutting and 

 line a-b indicates the condition of growing stock in the different 

 lots at this partictilar time. 



The line X between the 40 per cent and the 24 per cent in 

 the above case should be dominated by good silviculture, i. e., it 

 is fixed by the period of return. 



The line Y depends on market and is of no real consequence or 

 value. 



To caU the growing stock left after cutting a "reserve," and 

 speaking thus of a reserve of 24 per cent (in the above case) is 

 both unfortunate and misleading. A reserve is usually some- 

 thing ready and available but held back merely to have it readv 



