92 



(S) Possibility fixed by numler of trees oi* by volume. — 

 The mirober of trees or therolume of material whicli is to be 

 felled may, 'when precision is required, be calculated in a 

 variety of different ways. It will be sufficient here to indi- 

 cate one or two practical methods, which have found appli- 

 cation in India and elsewhere. The various methods to be 

 dealt with may be classified as follows :-— 



Possibility by number of trees — 



(«') Limitation of fellings determined by rate of 

 growth ; 



(n) Brandis' method. 



Possibility by volume— 



{iii) The Trench method ; 

 (i«) Von. Mantel's method. 



The prescription of the possibility by volume possesses 

 the advantage that it secures a more equal outturn from 

 year to year ; but this in India is often a matter of com- 

 paratively small importance. On the other hand, the appli- 

 cation of the voluaietrio method requires nice calculations 

 based on exact measurement and enumeration of the whole 

 standing crop ; and this diBBcult and expensive undertaking 

 must be repeated periodically. For this reason, and because 

 frequently in a mixed crop only one species is exploitable or 

 only trees of large size are saleable, the volumetric method 

 is in India under present conditions of forestry inferior to 

 that of prescribing the possibility by number of trees. 



(*) Limitation of fellings determined by the rate of growth. 



It was explained, when discussing at pages 2Ji and 26 the 

 formation of the growing stock, that, in a normal forest, 

 the number of trees which attain exploitable dimensions in 

 a given period practically represents the possibility of the 

 forest for that period. As it is possible to estimate, for a 

 short period in advance, the number of trees in a forest 

 that will become exploitable and to determine with some 

 accuracy whether the crop approaches the normal type or 

 not, the principle may, in some oases, be usefully applied 

 to selection working in forests in which the trees can be 

 enumerated. 



Suppose a forest in which treeg of all ages aro well represented and fairly evenly 

 •distributed, and in wbioh the rate of growth is such that in the course of 30 years 



