150 THS OENEEAL WORKING SCHEME. 



year. For the purpose of calculation, therefore, it may be assumed 

 that all the trees will be felled simultaneously at the middle of the 

 Period. Again we may be allowed to take for granted that the 

 future annual increment of trees near their term of exploitabihty 

 is the same as their actual average annual increment up to date. 

 Thus to obtain the total future increment we have simply to 

 multiply this average annual increment by half the number of 

 years in the Period. It is obvious that the determination of the 

 future increment must be made separately for each compartment. 



The yield of the annual cuttings is, therefore, found by dividing 

 by the number of years forming a Period the sum of the two 

 following quantities : — 



(i) The standing material or actual contents. 



(ii) The probable additional growth of the standing material, 

 or iuture increment. 



It is always easy to determine actual contents with a sufficient 

 degree of approximation, whereas the future increment can never 

 be estimated with any approach to accuracy. For this reason, unless 

 special circumstances demand the contrary, no account at all should 

 be taken of the future increment, since it is always better to be 

 under the mark than to run the risk of erring on the fatal side of 

 excess. Besides, the yield of windfalls, dead timber, and other trees, 

 the exploitation of which cannot be foreseen, proves to be, in the 

 long run, a complete set off against the neglected future increment. 

 Lastly, this increment does utimately enter into our calculations 

 ■when the standing trees are again measured at the verification of 

 the annual yield during the course of the same Period, and must then 

 permanently raise the figure of the yield for the remaining years of 

 that Period. The natural consequence is that the outturn of produce 

 goes on increasing by small and moderate additions at regular 

 intervals, a result greatly to H)e desired in the organisation of 

 every forest. 



Simultaneously with the volumetric cuttings, which furnish the 

 yield of principal produce, other operations, termed by us Improvement 

 Cuttings, such as Thinnings, for example, must be made in various 

 portions of the Working Circle, and can only furnish accessory 



