89 

 1^ J^4[^gu£2L'I^«^ '"^'°"''"* '•'''•'*'"'' *""• S"-"" *•" ""« "<"« "^1 



26» — 625 — 70 trees, and the volume of wood will be 



70 X 18o = 9,450 cubic feet. This is the growth of 150 years. The average mean 



annual production of each acre, therefore, amounts to ~^ = 63 cubic feet. 



In a selection- worked forest the rate of growth is exceedingly diflScult, we may 

 Bay impossible, to determine accurately, because of the inequalities in the growth of 

 the trees at different stages of their existence. Bat this is no reason for not attempt- 

 ing to estimate the growth, making due allowances for probable error. It is hardly 

 necessary to state that if there existed in the neighbourhood of the selection-worked 

 forest a mature regular high forest of the same species and growing under similar 

 conditions, the productive capacity of the soil could be determined more easily and 

 with greater accuracy by felling and cubing the wood upon a known area. Moreover 

 it would be possible to ascertain, from a regular crop of the kind, the number of 

 exploitable trees that can grow at the same time on one acre. 



Eetnrning to the forest cited as an example, the area of the blanks, roads, occu- 

 pied lands, Ac, has been ascertained by survey to be 210 acres. The productive 

 wooded surface would thus be reduced to 1,600 acres, and the average annual produc- 

 tion of the whole area would then be 1,600 x 63 cubic feet = 100 800 cubic (eet. 

 We might stop here and prescribe the removal annually of this volume— which is by 

 assumption equal to the annual production— from the entire area, trusting that the 

 forest would produce the same quantity and thus repair the loss. And, if the forest 

 were perfectly constituted and contained in the necessary proportions trees of every 

 size and stage of growth, no harm would result from this procedure. But such a state 

 of things is not often found, and it is impossible to say exactly how far the actual 

 approaches to the ideal C(mdition ; whether there are, for instance, a sufficient number 

 of trees of 3 feet in diameter to furnish 100,800 cubic feet of wood each year during 

 the time that isrequired for the trees of the next (say If feet diameter) stage to 

 attainthe exploitable dimensions ; that the trees of the next lower stage are sufficient 

 in their turn ; and so on. 



The yield mast therefore be fixed in number of trees. The annual production 

 of the soil being 63 cubic feet per acre, and an exploitable fir tree of 2 feet m. diameter 

 having a volume of 135 cubic feet, the annual yield of each acre in trees will be 

 63 ^135 ^ 047, and, for the entire wooded area, the annual yield will be 0'47 X 1,600 

 = 752 exploitable trees. 



It would usually be impossible, without great loss and inconvenience, to spread 

 the fellings each year over the entire area of the forest. We will suppose, therefore, 

 that the annual fellings are limited to one-tenth of the entire area, and that ten years 

 are allowed to elapse between sacce!>Bive fellings in the same area. As we have assum- 

 ed that there are in every 100 trees 90 firs and 10 oaks, the provisions of the working- 

 plan as regards the fellings might be summed up as follows : — 



" Each year there will be felled by the selection method, on successive annual 

 coupes of one-tenth the area of the forest, 752 trees^ via., 677 firs and 75 oaks." 



No limit as tu the si^e of the trees felled need be fixed ; but in each coupe the 

 dead or dying trees are felled first, and then a sufficiency of the largest trees to com- 

 plete the prescribed number, which in no case should be exceeded. This system of not 

 fixing any limit to the size, while strictly limiting the number, is chavacteristio of the 

 mefhod by the application of which the crops, in the poorer portions of the forest, 

 will become richer. Where the trees are small, the same number of stems will contain 

 a less volume of wood ; while, where the crop is rich in large trees, a greater volume 

 than the normal production will be felled. The crop will tend to become uniform 

 throughout, and to assume the normal state of one exploited at an average age of 

 150 years, which is the number of years that the trees require in order to attain 

 2 feet in diameter, or the assumed exploitable size. There will usually be no danger 

 of all the large trees being felled at once, because all will not be found in one portion 

 of the crop. 



An examination of the valuation survey records of the number of trees in each 

 size class will show the average age or size at which trees have been exploited ; for 

 trees above this size will be rare. The record will also readily indicate whether or not 

 there are trees of the various size classes in numbers sufficient, as far as can be judged. 



