30R DETERMINATION AND REGULATION OF THE YIELD. 



system requires a higher rotation, than that to be abolished, 

 the returns will also be smaller, until the conversion has been 

 completed, and possibly even longer. Hence, before a change 

 of system is undertaken, it should be carefully considered, 

 whether the advantages expected from the change are likely 

 at least to compensate for the unavoidable disadvantages. 



The number of conversions from one sylvicultural system 

 to another, which are conceivable, is considerable, and it is 

 impossible to give any general rules of procedure. Whatever 

 the nature of the conversion may be, the only sure basis for the 

 determination of the expected yield is the annual cutting area. 

 Hence, the consideration of a few special cases will bring out 

 the essential points to be considered in each conversion : — 



a. Conversion of the High Forest Selection System into the High 

 Forest Compartment System. 



This conversion necessitates the substitution of even aged 

 for uneven aged woods, and it frequently involves the cutting 

 over of trees at an age differing from that, which is most 

 advantageous. To justify this sacrifice the compartment 

 system must offer decided advantages over the selection 

 system. 



It is usual to fix one rotation for the conversion, to divide 

 the rotation into periods of even lengths, and to allot to each 

 period a corresponding portion of the total area, with due 

 consideration of the condition of the several woods. As a rule, 

 the several age classes are not evenly distributed over a 

 selection forest; generally, more old wood is found in some 

 parts of the area, and more young wood in others. This 

 fact is taken advantage of in the allotment, that is to say, 

 Period I. receives those woods which contain most old trees, 

 especially those with little increment. Period H. receives 

 the woods which are richest in middle aged trees, and so on. 

 In effecting this allotment, a proper grouping of the future 

 age classes must not be overlooked. 



£ra»ip/c. ^Assuming the rotation to be 120 years and the 



