In the hypothetical case supposed, it might be necessary to secure some timber of the greatest bulk which could be obtained, and in order to this, that the trees yielding this should grow to the age of 150 years. But it might be desired rather to get as much wood from the forest as possible; and much more would be obtained in the course of 300 years by felling at the age of 75, and getting four crops of trees of that age than by felling all at 150, and getting two crops of trees at that age. By felling at 60, and leaving baliveaux for seed, several fellings of trees aged 90 — the age at which the trees yielded timber of the best quality— and fellings at the ages of 120 years, and 180 years, and 240 years, and 300 years, of timber of greater magnitude might be obtained, along with the coppice wood of six fellings in the course of 300 years, from baliveaux left growing at the first, the second, and the third successive fellings; which might be reserved exactly in such numbers as would yield the timber required • and the rapid growth of none of the others at an earlier age would be sacrificed. Or, again, it might be desired to get as large pecuniary returns from the forest as possible; and this might be secured by an improved quality, though in diminished quantity, and that the maximum quantity of wood of the requisite quality could be secured in the period named — 300 years, by felling the trees at the age of 100, and getting three crops of trees of that age off che ground, than by letting all grow to the age of 150; while larger timber required might be obtained by reserved baliveaux; and arrangements might be made for the felling of such of these as might be required, not only without detriment, but if properly managed, with benefit to the crops then growing. These are but a few of the simplest complications for which a director of operations prepares.
The director or projector of operations, with the data referred to before him, together with special requireaients such as those just alluded to, if any such there be, determines what period of time is to be assigned to the crops to be produced successively by the forests — in technical phrase, determines the regime, or if this has been pre-determined, determines the time to be allotted to a revolution, or cycle, from sowing through growth and successive thinnings to felling and resowing again. The number of years going to a complete revolution is very different under the coppice wood regime and under the regime of timber forest; and under each of these it may vary within a comparatively limited range, according to the kind of tree, the situation, the demand, and the vigour of growth. This, then, has to be determined next conditionally, at least, if not absolutely.
With this addition to the data an estimate is then made of what is called la possibility, or of the cubic measurement of the growth made year by year, or definite period of years throughout the period of the revolution; which supplies a measurement of the wood, which, without exceeding the yield, might be removed in the course of each of these years, or periods of years.