38 FORKST VAr,UATlON 



interest rate of five per cent is set instead of three, the Se of $29.80 

 changes to a negative quantity ; i. e., the same land and management 

 which gives to the land an income value of $29.80 per acre becomes 

 a losing business to the man who values his money at five per cent. 

 The same is illustrated by the following figures for spruce, site II 

 (Endres, p. 274). The income value of the land, Se, with an 80 

 year rotation is at 



3 % $105 per acre 



2^2% 17,'? per acre 



2 % 285 per acre 



b. Values of the Factors of Se, and Variation in these Fac- 

 tors under different conditions. 



I. The final cut, Yr, depends on the growth to produce the 

 crop and on market to pay for it. 



a. Both site and species affect the final cut. These possible 

 variations are laid down in the yield tables for different species at 

 least so far as volume and size or quality are concerned. In the 

 more modern tables and for the settled conditions of the Old World 

 they are commonly worked out for money values or made into mon- 

 ey yield tables. The yield tables giving size and volume of timber 

 per acre have been a matter of experience and growth. Even for 

 the different districts of central Europe they are being improved 

 continually and will be modified further with better methods of sil- 

 viculture, added experience and more accurate and extended statis- 

 tics. Nevertheless, for central Europe they are good now, quite the 

 best we have ; they are more reliable than farm yield tables and far 

 surpass in safety the forecasting of ordinary business enterprises. 

 In all new forest districts including the United States, data for yield 

 tables are gradually accumulating. Asa beginning the practice takes 

 what it finds in the wild woods and the assumption is that what 

 nature has produced unaided will be produced again on the same 

 land and by the same species. Since the wild woods generally do 

 not produce as much timber nor as good a quality, for ordinary 

 rotations, the figures of yield and growth are conservative. This 

 is doubly true of money yield tables. In fact money yield tables for 

 most parts of the United States where they are based on present 

 stumpage prices are conservative to the point of uselessness, as is 

 clearly shown by comparing present stumpage prices with those of 

 twenty-five years ago. 



