136 FORESTRY 



Regulation by Comparison with Normal Stock. 



Wholly differing from the allotment system is the method 

 of regulating the felling accounts by calculating with formulae. 

 This consists essentially of a contrast between the actual and 

 the normal stock. In the Austrian formula method, which 

 is the oldest of its kind, and still practised in that country, 

 the underlying principle is as follows : A normal growing 

 stock produces a normal increment, the amount of which, in 

 mature timber, should be removed ; but forest crops which 

 show a growing stock greater or less than the normal should 

 be more largely exploited or more carefully conserved, as 

 the case may be. If a surplus be present the formula is 



where Y is the annual yield, Ir the normal increment, which 

 is taken as equal to the final mean annual increment, Gr the 

 actual growing stock, Gn the normal growing stock, and r 

 the number of years in the rotation. 



Forest Working Plans 



The object of the working plan is to regulate the time 

 and manner in which the utilisation of the forest produce 

 should take place ; and as a necessary accompaniment to this, 

 for the assuring of a " sustained yield," particulars concerning 

 all operations about to be undertaken are here brought to- 

 gether in methodical fashion. The plan or scheme is capable 

 of differentiation into three divisions : 



(1) The General or Chief plan. 



(2) The Periodic plan. 



(3) The Annual plan. 



The first of these indicates the lines upon which the man- 

 agement is to be conducted. Its prescriptions extend over 

 the time occupied by the rotation ; only occasionally, when 

 the condition of a forest is very abnormal, its scope is pro- 



