EOTATION FOR QUALITATIVE EXPLOITABILITT. 97 



all, afifect the annual sum of production, for the judiciously thinned 

 crop, thanks to the full room for unimpeded development thus af- 

 forded to the conserved trees, makes as much growth as the un- 

 thinned crop would have done. Hence the yield of the thinnings is 

 so much over and above what could be obtained from the same crop, 

 if no thinnings at all were made. 



To resume in general terms what precedes, we may say that 

 experiments relating to the mean annual production of forests show 

 that the extreme limits between which this mean attains its maxi- 

 mum are, on the one hand, the young high-forest stage or the age 

 of complete fertility and, on the other, the natural opening out of 

 the leaf-canopy when the trees have reached complete maturity and 

 the soil begins to deteriorate by the reason of incomplete cover 

 overhead. 



SECTION II. 



Agb of Qualitative Exploitability. 



A tree presents its highest sum of utility for unit of volume 

 when it has reached the largest dimensions it can acquire while 

 etill remaining sound. For whatever it is, whether oak, silver fir 

 or any other species, its timber is then adapted for the most varied 

 purposes and is, as a rule, bouud to be used in such a manner as to 

 satisfy the most important wants. Now it is impossible to foretell 

 what precise use will be made of timber that is to be felled many 

 years Lence, or what other wants may not by that time arLse, that 

 will require the same wood. Hence the only sure way to produce 

 the most useful descriptions of timber is to grow trees of the largest 

 dimensions possible and that chiefly because they will thus be suited 

 for the greatest number of purposes possible. 



The wastage in working up timber being less in the case of 

 large logs, it follows that, volume for volume, large timber in the 

 log contains more utilisable material than pieces of smaller size. 

 This remark appHes with less or greater force according to the 

 species concerned ; for instance, it is much more important that oak 

 and pine, which contain comparatively a considerable proportion of 

 sap-wood, should be obtained of larger size than silver fir or beech 

 in the employment of which no difference U made between the. 

 13 



