90 THE SELECTION METHOD 



proportion to the increased length of the cycle. For example, 

 if 200 board feet per acre are removed when a given stand is 

 cut through annually, then 10 X 200 = 2000 board feet per 

 acre should be removed at each cutting if the cutting cycle is 

 changed to 10 years. If the amount to be cut on an annual 

 cutting cycle is known, then the cut for any other cycle can 

 be quickly secured by multiplying the length of cycle by the 

 annual cut per acre. 



The actual percentage of the volume removed in a selection 

 cutting is subject to great variation depending on the length 

 of the cutting cycle and the unit in which the volume is 

 expressed. When the board feet unit is employed 100 per cent 

 of the volume might be removed in a given cutting provided 

 the old age class included all the trees of merchantable dimen- 

 sions. More commonly on a cutting cycle of 10 to 20 years, 

 2 5 to 75 per cent of the board foot volume would be cut. 

 Expressed in terms of cubic feet the percentage would usually 

 range from 15 to 50 per cent. 



This leads to the question as to how the amount per acre 

 which can be cut should be determined. If all age classes are 

 represented each occupying the proper proportion of the 

 area it is easy to limit the cut. Either the annual growth or 

 the oldest age class could be removed each year, or the peri- 

 odic growth be removed at the end of each cutting cycle, 

 and sustained annual yield in an unevenaged stand be main- 

 tained indefinitely. The two (i.e., annual growth or oldest 

 age class) are identical in volume provided the proper pro- 

 portion exists between age classes. Unfortunately this ideal 

 stand is non-existent which makes more complicated the 

 problem of determining the amount to cut. The following 

 procedure is suggested.* 



* This question of limiting the cut or regulating the yield from a given arvu 

 falls under regulation and outside the province of silviculture. Yet under the 



