87 



diameter, being 17,867, the greatest number of trees (the 24,741 trees over 24 inches 

 being already exploitable) which can attain exploitable dimensions each year in the 

 immediate future is 17,867-J-30=:696 trees. This number, divided by the wooded 

 area of the forest expressed in acres, would give the average annual production of 

 exploitable trees per acre. Assuming this area to be 1,200 acres, the average annual 

 production per acre would be 596-f-l, 200=0*5 trees. It would be pcssible to compare 

 this figure with that of other similar forests, and thus to ascertain whether the 

 production was above or below what it ought to he. We will suppose that it is found 

 to be considerably in defect. It would follow that the forest is deficient in trees of 

 Class II, and also it would appear of Class III, as the number is about the same. 

 Class IV would, however, appear (a rough approximation only is possible) to be well 

 represented, and so would Class V. It may, therefore, be accepted that during (we 

 will assume) the next 60 years, until the crops of Class IV begin to he exploitable, the 

 fellings must be made with caution ; but that the crop will be thereafter fairly com- 

 plete if not altogether normal. This interval of 60 years is in fact a preparatory 

 period during which a provisional plan is required. 



As regards the sufficiency or otherwise of the existing exploitable stock, we will 

 suppose the felling rotation adopted to be a very long, say 30 years, and that the 

 whole area is subdivided into 30 portions each approximately equal in extent. Every 

 year there would pass from Class II into Class I and become exploitable something 

 less than 596 trees, or on one-thirtieth of the area wj=:i9 trees. Consequently, 

 immediately before the commencement of the second felling rotation and ever after, 

 the exploitable stock on the ground would be : — 



On the area felled over 30 years before 30x19 trees. 

 29 „ 29X19 „ 



28 „ 28x19 „ 



etc., etc., etc, 



, 2 „ 2X19 „ 



), „ »> 1 »> •"• '^ ■'" » 



The total number of exploitable trees left standing would therefore be — 

 19 X (30 + 29 + ... + 2 + 1) = 8.835 trees. 



Therefore the surplus stock is 24,741 - 8,835 = 15,906 trees. 



As however, the crop is defective in trees of Classes II and III, this surplus 

 oTipht if the trees can be preserved in a healthy condition, to be utilised during the 

 ™4.ol»'nf thP nreoaratorv period of 60 years. It would, therefore, be only permissible 

 To fell 15,906^ 60 = 265 trees of the surplus stock each year or, in all, 265 + 596 



~ ^ lWoreS"tocussion! as to the sufficiency of the stock already exploitable. 

 A^^L thp assumption that the stock of trees in Class II is normal. But suppose 

 ?h:maximumn"r of trees becoming exploitable each vear. viz., 596 is below 

 the no?m7production which should annually be about one tree an acre or 1,200 trees 

 in auT this case it would be desirable to preserve on the ground a corresponding 

 stock which would be, with a felling rotation of 30 years. -^ ( 30 + 29 + . . . . 1 } - 

 i,2H0f OQ . 1 1-^ = 18,600. Here again it would only be permissible to fell 

 /9A 7/tl —18 6001 -^ 60 = 102 trees of the surplus stock each year during the prepara^ 

 1 ' LnS ,o that the fellines would be reduced to 102 + 596 = about 700 trees a 

 tory period ; so that 'f« f "'"^T""' ^tock is deficient. If there were only, 



year. Again It might be that ^he e^P'o^ta^-le .t Ji ^^^^ y^ 



wewilUuppose 4 741 instead of 24,741 ^^P^""^^^ be verv deficient in mature 

 srk^^n£rs7o?60V^^"h;'fx;ioVable stock should be augmented by the 

 di^erence IS,600 4.H1 = 13^^^^^^^^^ ^J Lt^?^:^ 



;S notrote tlledlh ylarToi^e than about 596 -^231 = 365 trees. 



