6 THE THEORY AND PRACTICE OF WORKING PLANS 



Pressler's formula is exceedingly valuable for regulating 

 the cut in mixed, selection forests.* 



Whether the current annual or the mean annual increment 

 is to be determined depends on the method of regulating the 

 cut which is to be adopted. It is not usually necessary to deter- 

 mine painstakingly the exact increment of each stand, but rather 

 correctly to approximate the increment in each Working Unit — 

 i.e., the unit area for which the cut is to be regulated; for it 

 is evident that in comparison with the volume of merchantable 

 timber the increment is a relatively small amount. It is a use- 

 ful fact that in stands approaching maturity (not overmature) 

 the mean annual and current annual increment remains vir- 

 tually the same for about ten years; since the former is simply 



the volume divided by the age ( — j , a simple way is thereby 



opened to approximate the current annual increment in 

 mature, even-aged stands. 



Dr. Fernow in an article on " The Sciences Underlying 

 Forestry," f points out that the mean annual increment per 



cent, culminates when it is equal to — , in which a = age of the 



stand. This culmination occurs where the current annual 

 increment curve crosses the m.a.i. curve. Current annual 



increment = —— (Schneider), hence — - = or a = ^. This 



nd na a 4 



is a handy way to determine the age of maximum volume 



production. 



The Growing Stock 



Growing stock is a general term referring to the standing 

 timber upon a unit of area. When used in relation to problems 

 of management, it usually refers to the volume of standing 



* See " A Practical Application of Pressler's Formula," Forestry Quarterly, 

 Volume XIV, No. 2. 



t Forestry Quarterly, Vol. VII. No. i, pp. 23-33. 



