152 



PRACTICAL FOBE8T MANAGEMENT. 



Determi- 

 nation of 

 the rot a* 



tion. 



The 

 fell ing 

 cycle. 



The 



calcula- 

 tion of 

 the yield. 



The length of the rotation adopted must depend on the size of 

 tree required to yield the class of timber most in demand in the 

 market. This again depends on the quality of the site. If 20* 

 diameter is the exploitable size for quality I sal sites, it is useless 

 expecting the same size on quality IV sites. Hence the difficulty 

 of a fixed exploitable size, more especially in the case of hill sal 

 where the quality varies enormously over comparatively smal 

 areas. It is necessary to calculate the size of tree required and 

 the average time taken to produce this tree under the conditions 

 of regular high forest. In selection forest, trees reach the 

 exploitable size at very different ages, depending on the conditions 

 of their environment, and diameter is generally of more importance 

 than age. Hence the rotation adopted will approximate that 

 calculated for regular high forest growing on similar sites. 



Selection fellings should pass over the area of the working 

 circle in an orderly manner. Where the yield is calculated in 

 volume the extent of the fellings will determine the length of 

 time which elapses before any compartment comes again under 

 felling, although under modern practice no periodicity of the 

 fellings is prescribed and the Divisional Forest Officer may return 

 to any compartment in urgent need of felling. Where the yield 

 is regulated by area, the felling cycle becomes of considerable 

 importance. In the past this has varied from 10 to 30 years ; the 

 former is too short for the very extensive area of hill sal and 

 protection forest in the submontane divisions and the latter too 

 long. The length of the cycle is frequently taken as that necessary 

 for the trees of the diameter class approaching maturity to pass 

 into the next higher class and for regeneration to become estab- 

 lished after the previous felling. In general for the hills of the 

 submontane divisions a felling cycle of 20 years is suitable. 



No calculation of the periodic yield of each compartment in 

 accordance with the principles of the " Methodo du Controle " 

 is under our conditions of working a practical proposition. With 

 frequent revisions of working plans and re-enumerations it will in 



