EOTATION FOR OTTANTITATIVE ■EXPLOITABILITT. '95 



the last 20 or 30 years. Hence such crops are not in the condition 

 in which they might have been, had tthey been thinned regularly 

 from aa earlier age as soon as Lhincirags hecame necessary. More- 

 over the degree of severity of a tbinniBg is not without ite influence 

 on the total production of the soil, the extent of this influence being 

 still bwt'little known. 



Butdf a complete merles of experiments can rarely he made, 

 partial experiment-s of this kind are frequently possible and furnish 

 general data of great importance. Thus nothing is easier than to 

 find out the cubical contents of a uniform crop together with its 

 age. And as the quantity of the produce yielded by -the thinnings 

 already made is on record, a araall arithmetical calculation gives 

 approximately the mean annual production since the appearance of 

 thecrop. By this means we -have been able to ascertain that the 

 Quantitative Exploitability of high forests of our large species 

 generally is reached towards ithe end of the first century and is the 

 longer delayed, the slower these forests thin themselves under the 

 action of natural forces alone. Again we have copses exploited at 

 all ages between 20 and 40 years, and there are even many in dif- 

 ferent localities which have been left standing with a view to con- 

 version into high forest and which are now from 40 to 80 years old. 

 These copses show that the mean annual production of a simple 

 copse goes on increasing beyond the age at which it ought to be 

 exploited to obtain an abundant regrowth from the stool ; and, more 

 than this, that the Quantitative Exploitability of copses is attained 

 ■only tovards their fiftieth year, a little earlier or a little later, 

 according to the component species and the prevailing classes of soil. 



It is even possible to tell by certain peculiarities or physical 

 signs whether a given crop has become quantitatively exploitable. 

 At this period it has passed the stage during which growth in height 

 ds rapid, and it has acquired nearly all its natural length of bole ; 

 it has become completely fertile, and, growth in height being practi- 

 cally at a stand still, the forest has begun to tiin itself naturally. 



Thin-nings made by the hand of man precipitate this result ; but 

 the point on which their importance chiefly rests is that they obtain 

 from the forest and render available for consumption a larger 

 quantity of produce, and this too at an earlier age, than if the forest 

 were allowed to thin itself by the natural struggle for existence 



