THE CALCULATION OF THE YIELD. 153 



the future be possible to ascertain the actual increment of every com- 

 partment and to calculate the yield in" accordance with the above 

 ruethod, but still the yield must be calculated for the working 

 circle as a whole and each- compartment felled on its merits. For 

 the present where a volume yield is required, this yield may be 

 calculated by some modification of Von Mantel's, Heyer's or any of 

 the methods described in Chapter VI, depending on the data 

 available. In other cases more especially in protection forests an 

 area yield will suffice. 



The execution of the fellings will vary with the species and _ 

 the silvicultural idea on which the management rests. A general method 



example for sal is given as follows : of 



executing 



(1) Subject to silvicultural considerations, the maintenance the 



of the crop, and the silvicultural idea, the class of tree 

 on which fellings should bear is indicated by the graph 

 in the compartment history showing the actual growing 

 stock compared with the normal. 



(2) Where the crop is mature and regeneration required, the 



canopy will be opened so as to obtain groups of young 

 growth of sufficient size. 



(3) Where mature trees are standing over a younger crop 



they should be removed in selection. 



(4) All bad trees not actually required for seed should be 



marked and all dead and dying trees removed. 



(5) All trees obviously out of place, poles or middle-aged trees 



deforming good regular groups of younger age classes 

 may be felled subject to rule (1). 



(6) Pole crops should be thinned. 



(7) All classes of trees down to 8" diameter count against 



the prescribed yield. 



It will thus be seen that in every compartment every sort of 

 silvicultural operation has to be carried out at one and the same 

 time and to do this well requires exceptional ability. 



