482 APPENDIX 



made on test trees from time to time during the course of our trip. These indicate 

 that for a dominant tree with annual rings 0.04 inch in breadth there is an annual 

 increment of 0.9. According to this the current annual increment at present amounts 

 to 130 cubic feet per acre and if that proportion holds true for only three-quarters the 

 volume of the stand — the dominant trees — to (in round numbers) 100 cubic feet 

 per acre. 



This is almost the same as that which is determined from complete volume tables 

 and yield statistics as the mean annual increment. The two kinds of increment are 

 seen — contrary to the commonly accepted belief — at the age of 200 years to be at the 

 point of crossing and agreement. 



If the foregoing propositions^cannot, because of the lack of sufficient data, be definitely 

 proven, yet enough observations have been made to justify the conclusion that the 

 current annual increment of the oak under the existing conditions of the site and the 

 indicated character of the stands exhibits a uniform dechne. The faUing off in current 

 annual increment has taken place very gradually; far more gradually than most yield 

 tables indicate for German forests, where the oak is much less crowded in the older age 



To a yet greater extent is this evident in the case of mean annual increment. This, 

 in the case above cited, has not changed appreciably for a full century. That sort of 

 maturity known as exploitabilite absolue gives entirely too indefinite results, in that 

 account; it may be placed at as early an age as 80 years or as late as 200. 



(6) QUALITY INCREMENT 



Of greater importance than the volume incfement as a determining factor of the 

 age of maturity is the value increment. The French management shows conclusively 

 that in their own forests especial importance is attached to the production of good quality 

 of product. The less private individuals are inclined to grow heavy timber, the more 

 does the State find itself confronted with the necessity of producing this economically 

 indispensable product. The best way to get an idea of the progressive increase in value 

 is to study the average prices paid for wood where the trees of varying size are valued 

 separately. The approximate selling price of trees of various girths are as follows: 



Trees of 200 cm. circumference (65 cm. diameter), 65 francs per cu. m." 



Trees of 100-200 cm. circumference (33-36 cm. diameter), 45 francs per cu. m. 



Trees under 100 cm. circumference (under 33 cm. diameter), 30 francs per cu. m. 



These classes are too indefinite to afford any precise idea of the value increment. 

 They show, however, that the increase in value bears a direct relation to the increase 

 in size. Trees whose diameter increases from 20 to 24 inches increase in value about 

 40 per cent. With annual rings 0.05 inch in width about 35 years are required to 

 produce a diameter increment of 3.9 inches. Hence the yearly increase in value can 

 be placed at a good 1 per cent. 



(c) THE INTEREST PAID ON THE GROWING STOCK 



It is not really possible to fix the length of the rotation period intelligently without 

 a study of the economic principles upon which the practice is based. The kernel of 



13 According to Schwappach's yield tables : 

 On first quality site at 



the age of 60 80 100 120 140 160 ISO 200 



The current annual in- ] Wood more than 



crement amounts to . . 10.2 9.2 6.8 5.2 4.6 3.8 3.4 2.8 m.^ 7 cm. in diameter 

 The mean annual incre- | at the small end 



ment 4.6 5.9 6.3 6.2 6.0 5.8 5.5 5 . 3 m.^ ] (Derbholz) 



"26-inch trees, $12.55; 13-26-inch trees, $8.70; under 13-inch trees, $5.80. 



