The succeeding crops, moreover, were not always found equal in quantity to the preceding, while they were also much inferior in quality in consequence of the irregularity in regard to denseness in which they grew up — in some places sparse, in others so dense that they could neither attain to good proportions nor acquire a firm texture. These evils it was sought to remedy by giving to every patch or plot in the forest the treatment it specially required, combining those which were in like conditions and conveniently situated, treating them as if they constituted a continuous wood —modifying the arrangement of a tire et aire to meet the requirements of this development of that system, and adding the products of thinnings and partial fellings in patches or plots, in which these were practised, to the products of the successive definitive fellings in others, or rather adding these to those to complete the supply required without preventing natural reproduction and sustained production.
In the accomplishment of this there are sundry operations necessary in any case, but more especially when it is desired to secure all the advantages of the system. Circumstances may determine the order in which these may be attended to, and it appears to me to be a matter of indifference in what order I now detail them.
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Let it be supposed that it is virgin forest which is to be exploited — it is ascertained, by survey and inspection, of what kinds of trees it is composed; what age, or different ages, the different kinds of trees are; in what condition they are; what measure of vigour of growth they manifest, and what are the promises, in regard to this measure of vigour being maintained or increased in coming years, supplied by the nature of the soil and the situation of the trees. Thus a general idea of the peuplement of the forest is obtained. By another series of observations which may have previously been made in connection with, or in preparation for, the exploitation of other woods, or, which if not previously made, must be made now, it must be ascertained in regard to the kind or different kinds of trees of which the peuplement of the forest consists — what increase of cubic contents these make in the course of a year, or of any definite number of years— say five or ten — at all stages of growth, from that of a sapling to that of an old tree beginning to decay; and in connection with this, by deduction from data thus obtained or by separate observation, it must be ascertained to what age and magnitude the kind of tree growing there may attain without decay; at what age the annual increase becomes so diminished that a greater production of wood in a given period of considerable duration may be obtained by felling and raising a new crop, than by allowing the trees to go on growing; at what age of growth the wood is of best quality for the purpose for which it is required; and at what age a maximum of wood of such superior quality would be secured by then felling the tree.
In illustration of what may thus be learned I may adduce a hypothetical case. Suppose, what is likely to be the case,, that a tree in its growth makes an increasing increment of cubic contents year by year, and decade by decade, up to the age of sixty, making more wood between 10 and 20 than between 1 and 10, more between 20 and 30 than between 10 and 20, and so on continuously, more between 50 and 60 than between 40 and 50: it may be found that, though continuing to make increase, it does not make a greater increment between 60 and 70 than it did between 30 and 40, and that, though still making increase, this is now in continuously diminishing quantity, until decay having begun after a lapse of years, it loses more by decay than it makes by growth. But it may be found that though the rate of increase of quantity was reversed after 60 years of growth, the quality continued to improve for thirty years and more thereafter; and also that it was only when the tree had attained the age of 150 years that it had attained the size necessary to yield timber of the size required for some special purpose for which it was needed. All of the information thus obtained may be turned to account in determining the treatment to be given to the forest in exploitation, though it may, or it may not, all be required; but the same may be said of a great deal of the work of subordinates in any work.