Mr Cruickshank’s opinions regarding pruning and thinning are generally not very incorrect. His commencing sentence on pruning, that “most deciduous trees, if left to themselves, have a tendency to grow with short trunks, containing little timber, and to waste their strength on large unwieldy tops,” would, however, lead us to form a different conclusion. The very tall, clean, straight, deciduous trees, in the American forests, give a sufficient answer to this. We like his remark respecting thinning, that “it is only efficacious when applied as a preventive, not as a cure.”
Mr Cruickshank next brings forward his plan of raising oak forest, which appears to have been his own invention, although invented before. Whenever mice and other gnawers (glires) are not very abundant, it, if properly executed, would seem to be the best method of raising oak forest; and, indeed, in many situations, the only practicable one. Mr Cruickshank’s method coincides nearly with Mr Sang’s, only he does not carry his system of protection so far as Mr Sang, in first raising belts of the most hardy kinds of timber, distributed to windward of, and intersecting the place intended to be planted, in such a manner as to afford the best possible shelter from the coldest most destructive {352} winds. Mr Cruickshank, who has never carried his plan into execution, except in an experiment embracing a few yards, directs that the ground intended for oak forest should first be planted with Scots fir and larch, about 4000 to the acre, by the single-notch process, previously described, which can be accomplished under L. 1 per acre. As soon as these have risen to four feet in height, he prepares patches about two feet square and ten feet distant in the interstices, by digging the soil over, and mixing a spadeful of slaked lime carefully with the mould, taking out a tree whenever the interstices do not suit for the patches. He then plants, in the end of March or beginning of April, five acorns in each patch, about an inch deep, one in the centre, and the other four in the angles of a foot square, and gives them no farther attention for two years, except removing any overhanging low fir branch. He then goes over the patches, cutting out all the supernumerary plants, a few inches below the surface, leaving the most promising one on each patch, being very careful not to disturb any of its roots in cutting out the others. As these oak plants extend in size, he gradually removes the fir.
Excepting the bare plan itself, which is certainly very plausible, there is nothing in the description {353} of the practice—the preparation of the patches of ground to receive the seed and the subsequent management—which merits attention. His very particular interdiction of the use of manure is, to say the least of it, injudicious—as if it signified to the plant whether it were forced by the use of lime, or by a little putrescent manure, both of which Mr Withers would consider very advantageous; or as if there were much fear on our poor exposed wastes of erring on the side of rendering the plant delicate from over luxuriance; its constitution, on the contrary, would rather be strengthened. Mr Cruickshank, in directing the removal of the fir nurses, one thousand per acre to stand till they have reached twenty-five years, fit for roofing of cottages, and similar purposes; and five hundred till they have reached thirty-five years; his dividing a slaked boll of lime into five hundred spadefuls; and his bestowing no hoeing or weeding upon his seedlings, would show, without his admitting it, that he had never practised this mode of forming plantation.
Prefacing this system of rearing oak forest, Mr Cruickshank in rather a clever manner points out its advantages, and also the disadvantages and consequent failures of planting young oak trees in exposed situations. But after all his eulogy, we think he has {354} left something unsaid. The great disadvantage attending transplanting oaks to situations not very favourable to their growth, is, that the plant which, under any circumstances, receives irreparable and often mortal harm, from the severe injuries of removal, has to contend, in this mutilated condition, at the same time with the uninjured occupiers of the soil (the nurses or the native weeds), and with the unpropitious situation; whereas, when the plant springs up from the acorn a native, especially when it is assisted at first by weeding or hoeing, the part above ground being always in proportion to that below, and receiving due nourishment, it contends with the occupiers on more equal terms, and encounters the sterility of the soil, or the severity of the climate, with all its natural powers unimpaired.
As it is the natural condition of the seedling to grow up under the shelter of the parent tree, so also does it happen, that it rises under this shelter with greater luxuriance and vigour than when exposed to the evaporation, and parching sun, and battering wind, of the bare country.
We have admired the beautiful, straight, luxuriant, shoots of the young hollies, thrown out under shelter, and have compared them with the dry stunted shoots of the young holly in the open country, though in the former case their roots had to contend {355} with the roots of larger trees, and in the latter they had the soil to themselves. Experience has proved, that in exposed bleak situations, shelter is necessary to young plants. Transplanted oaks among the roots of young trees, so large as to afford sufficient shelter, very frequently do not succeed, at least without the utmost care in the transplanting, and a considerable deal of labour to prevent the roots of the shelter trees from starving the transplanted ones, unless a very propitious moist summer follow the transplanting. Raising from the seed, which obviates all this, seems therefore the only conveniently practicable way. Yet it must be owned, that the system of raising forests in situ from the seed, appears, as yet, much more successful on paper than on our hills and moors.
In endeavouring to confute the opinion, that the oak will not grow throughout Scotland, but in the milder and more propitious situations, Mr Cruickshank adduces the well-known fact, that large oak timber is found in almost every peat-moss.
This is a fact worth tracing to its cause. Under Nature’s own conduct, trees advance considerably further into elevated or cold inhospitable regions, than they would otherwise do, by means of the mutual shelter, and of the more hardy kinds acting as an advance guard. Yet there is a limit to this, as the {356} power of ripening seed is not increased by shelter in proportion to the power of growing—perhaps not at all; we instance the Spanish chestnut, which has scarcely ever been known to ripen seed in Scotland. Seed-grown trees will, therefore, under Nature’s arrangement, not be found extending much beyond the line of seed ripening. From nuts, acorns, and other seeds, fully developed, being found in elevated mosses in this country, other causes than shelter appear to have existed.
Before this country was so much overrun by men and oxen, a great deal of timber had existed, covering much of the superior land which is now under tillage. This consisted chiefly of the oak, Scots fir, birch, hazel, and alder,—the oak extending northward and to elevations, and ripening seed, and attaining to a size which it does not now do, either wild or cultivated, in the same latitude, neither here nor in any other portion of the world; which, along with some other facts, lead to the supposition, that the climate has changed a little,—in part, possibly, as we have before stated, from the gradual formation of peat, to which, overthrown oak forest, from the abundance of the tannin principle, has a great disposing influence, even under a warmer climate than present Scotland. The highest latitude to which a tree, or any other kind of plant, reproducing by seed, {357} naturally extends, depending on the ripening of the seed, and also on the power of occupancy, is however different from that where it will grow, when ripe seeds are procured from the coldest place where they ripen, and all the competitors removed; and under the system of shelter belts, hardy pine nurses, and seeds from the nearest place where they ripen, we have no doubt that oaks may be extended to a colder situation than Nature herself would have placed them in. For the higher more bleak portion of the country, we would recommend acorns grown in Scotland, in preference to those imported from England. We have several times observed wheat, the seed of which had been imported from England, sustain blight and other injuries in a cold moist autumn, when a portion of the same field, sown of Scots seed, at the same time as the other, and under the very same circumstances, was entirely free from injury. English acorns are also frequently heated in the casks in which they are imported, which must impair their vigour[66]. {358}
The part of Mr Cruickshank’s volume which we have analyzed, does not extend much beyond the first half: this portion is well worth a perusal. We have merely glanced over the remainder: it is a make-up scarce worth noticing. The language, on the whole, is easy and plain; and although the volume contains a considerable number of errors, in the pointing out of which we have not been sparing, yet will it form an excellent planter’s assistant to people who have ground to plant, and are ignorant of the process of planting.