544 Forestry Quarterly. 



conditionally so. There are always a number of unknown quan- 

 tities in the equations which represent economic relations. This 

 is especially true in soil values and stand values ; both are cause 

 and result interchangeably. The rotation also shows this causal 

 relation : on one side it is the effect of the interest on the stock and 

 hence of the stock itself ; on the other side, it is the cause of the 

 amount of stock. This peculiar connection of cause and effect 

 renders the mathematical treatment of economic problems in con- 

 nection with organic nature so difficult, sometimes impossible. 

 Similarly agricultural soilrents are a result of grain prices and at 

 the same time the soilrent is figured as part of the price. 



Nevertheless, in forest valuation for purchase, sale or exchange, 

 definite data must be found, i. e. certain assumptions must be and 

 are made on which the calculation progresses ; e. g. the assumption 

 is made generally that the error in the use of present values may 

 be compensated by using lower interest rates : it is impossible in 

 such valuations to get away from the subjective conceptions of 

 the valuer; hence there are always various values figured even if 

 the data or facts are the same. 



The above formula, however, was to serve not in purchases or 

 sales but in forest organization, when data are handled differently : 

 mathematical calculations become of minor import, soil physics, 

 physiology, economy which cannot be expressed by mathematical 

 signs, become more prominent and expert opinion will prevail in 

 making working plans, in choice of species, of methods of man- 

 agement, rotation, etc., but it is desirable to base as far as pos- 

 sible the expert opinion on carefully ascertained economic data, 

 especially as regards volumes and values of the stands and their 

 increment, and place them into a formula for precision of expres- 

 sion, not, however, making the formula paramount. He refers 

 on this position to the well-known statement of Karl Heyer, whose 

 budget formula employed in the sense of its author will remain as 

 useful as will Martin's own formula. 



Compared with the soilrent formula, derived from single, 

 regular stands unchanging in their condition and in intermittent 

 management — not necessarily a strict sustained yield management 

 the single stands the author claims his formula, in spite of its de- 

 fects, superior wherever, as in large State administrations, annual 

 management — not necessarily a strict sustained yield management 

 — is the rule. 



