ROTATION FOR NATIONAL EXPLOITABILITT. 101 



test that its utility has also increased. It follows then that whether- 

 we wish to obtain the highest sum of utilixy or the largest 

 receipts, we have never any reason tO' exploit a forest before its 

 timber has attained the first class-si^e of commerce. The age 

 at which this occurs is the lowest limit for a rotation that realises 

 the conditions of Natitional Exploitabiliity. 



We must except from these remarks those forests, of which the- 

 soil is not good enough to enable the trees to attain the required 

 size. It is obvious that in no case ought the rotation to exceed th& 

 age of maturity, but since the thicker a log isj the more useful it is, 

 it follows that the first-class size of commerce is necessarily as nearly 

 as possible that, which that species generally attains before begin- 

 ning to decay. It thus happens that, as a rule, the maturity of a 

 canopied forest is reached soon after the age at which first-class 

 marketable size is attained, and just before that at which it begins 

 to decay. The interval between these two ages is more or less long, 

 depending on the species and forests concerned. In any case, the 

 moment when decay begins is the superior limit for the rotation 

 corresponding to National Exploitability. 



It is thus easy to determine this rotation with perfect certainty 

 within a very few years of the real figure. By keeping as near as 

 possible to the age of the maturity of the crops concerned, there is 

 no danger of making a mistake. 



The maturity of a canopied-forest, like that of a solitary tree, 

 is also manifested by a marked loss of vigour of growth. The leaf- 

 canopy becomes lighter than during the period of sustained vigour ; 

 seedlings of the principal species now make their appearance, if they 

 did not exist before ; or, if they did exist before, they now begin to 

 push forward. But these signs, although generally similar for all 

 forests, present certain characteristic differences according to the 

 species of trees composing any particular forest. 



The two limits of age between which the National Exploitability 

 of a forest is comprised, viz., that at which the standing timber 

 acquires first-class dimensions from a commercial point of view, and 

 that at which decay sets in, always offer two definite starting points 

 by means of which to determine the rotation. If we work from the 

 lower limit, we must ascertain by careful ring-countings on felled 



