95 



■dimensions each year in the immediate fnture is the total 

 number in Class II (the size-class next below that of which 

 all the trees are exploitable) divided by the number of years 

 required for trees of the lowest dimensions of this class to 

 become exploitable. This is then tlie possibility of the crop 

 for tbe time being ; aud it must be estimated — from the 

 average production of other similar forests for instance — 

 whether the result so obtained is above or below the normal 

 or potential possibility, and the number of trees to be felled 

 should be increased or diminished accordingly. With, a 

 view to estimating whether the age-classes are suitably 

 graduated or not, the number of trees in Class II may be 

 compared with those in the lower and higher classes. Finally, 

 as regards the sufficiency or insuflBcienoy of the stock already 

 exploitable, it must be remembered that, in a normal forest in 

 which the age-elasses occupied equal areas, there would be no 

 trees above the exploitable size on the ground immediately 

 after felling, and only one year's growth immediately before 

 the next felling. In a selection-worked forest, owing to the 

 trees of difEerent ages being distributed all over the area, 

 this would only be the case where the whole area of the forest 

 was worked over each year. Ordinarily, however, as already 

 explained, the entire forest is gone over in a number of years ; 

 and consequently it is only on the portion of the area felled 

 over twelve months previously that there is one year's 

 growth of exploitable trees, on the next area there is two 

 years' growth, on the next three, and so on up to the limit of 

 the felling rotation. Knowing, therefore, the number of 

 trees of Class II which annually attain exploitable dimensions, 

 we can calculate the normal exploitable stock and thus ascer- 

 tain whether the actual exploitable stock is sufficient, insuflS.- 

 xsient or superabundant relatively to the stock in Class II. 

 If superabundant, the excess can be utilised at once or in 

 several years according as the lower stages of growth are 

 suflBcient or insufficient. If insuffi.cient, less than the normal 

 possibility should be removed. 



The crop already taken as an example will serve to illustrate this tunthod of 

 analysis. Tho' number of trees below exploitaljle dimensions, 18 to 24 inches in 

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

 beinff already expluilable) which can Httain exploitable dimensions each year in the 

 immediate future is 17,867-7-30=596 trees. This number, divided by the wooded 

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

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

 production per acre would be o96-t-1,2()0=0'5 trees. It would be possible to compare 

 this fignre with that of otl>er siuiibir forests, and thus to ascert^iin whether tbe 

 production was above or below what it ought to be. We will suppose that it is foand 



