GERMAN COMMENT ON FRENCH FORESTRY 481 



No basis for the rotation period in the forest under discussion has been described by 

 the advocates of the French State forest policy, at least not definitely enough to be 

 repeated here. We can get an idea of it only from the condition of the stand and the 

 information given in the Uterature. Tassy,"* discusses the determination of the cutting 

 age (exploiiabilite) in the following words: "The volume of the wood which has been 

 produced, its economic value (utility), its sale value (vaieur venale), and the ratio between 

 its value and that of the capital from which it comes are the various factors which, 

 individually or collectively, must be borne in mind if it is desired to make the greatest 

 profit from the management of the forest. These several factors correspond to four 

 objects of management: First, management for the greatest volume production; second, 

 that for the highest technical value; third, that for the greatest money revenue; fourth, 

 that for the largest interest on the investment.'' As is everywhere the case, the rotation 

 periods in the French forest management, as well, are dependent upon the progress of 

 volume and value increment and the interest paid on the forest capital. The question 

 of rotation periods in France cannot be understood and discussed further without 

 entering into discussion of the peculiar conditions whose influence upon the condition 

 of the forest is nowhere more pronounced than here (a fact which is not brought out 

 in the foregoing quotation). 



(o) VOLUME INCREMENT 



This is everywhere a fundamental determining factor of the length of the rotation 

 period. G. L. Hartig's teaching, that upon given areas there is always a maximum 

 increment which should be produced, may always be accepted as essentially correct. 

 Even if the value of the product and the intwest paid on the capital be taken into 

 consideration yet the volume increment is still an essential determining factor. If 

 it be reduced the volume and value of the product from which revenue is obtained will 

 likewise both suffer a diminution. 



The mean increment (accroissement moyen) is looked upon as that which shall decide 

 the age of maturity under the French system of forest management. "The rotation 

 period giving the greatest volume production {exploiiabilite ahsolue) is indicated by 

 the age at which the greatest mean increment is produced." According to that the 

 proper rotation age occurs in that period when the current increment is falling off. It 

 corresponds to that age when the ciu'rent increment is equal to the mean increment. 



We have but little definite information which bears upon the problem of current incre- 

 ment or upon the principles of mean increment. In the forest region of Belllme and 

 Berce exact studies were available chiefly for a 200-year-old oak stand with an admix- 

 ture of a few beeches and a ground cover of young beech, giving its increment and 

 previous utiUzation. The number of trees per hectare amoxmted to 198 (80 per acre), 

 the volume of wood larger than 28 inches at the small end (Derbholz) 13,875 cubic feet 

 per acre. The actual utilization is given as 6,200 cubic feet per acre, the total possible 

 as 20,080 cubic feet per acre. According to this the mean increment amounts to 96 

 cubic feet per acre. As a matter of fact the actual volume production was greater 

 because during the 200-year period it is very Ukely that wood was utilized of which 

 partial or no accounts were kept. 



The current increment in stands more than 200 years old has doubtless heretofore 

 not been determined because of the falling off in growth occurring at this time. The 

 principal cause of this falling off is evidently the abundant flower- and seed-production. 

 Otherwise the plant foods of the soil are completely utilized by the roots, and the air 

 space by the crowns; hence any very great reduction in that increment which corre- 

 sponds to the site is not to be expected. This supposition is substantiated by studies 



" I. c. Deuxihne itvde: de I'exploitahiliti (Second article: on the age of maturity). 



