Page:Encyclopædia Britannica, Ninth Edition, v. 2.djvu/343

ARBORICULTURE 323 carefully prepare the soil for the trees, removing the weeds afterwards for two or three years till the branches begin to cover the ground ; in which state we should leave it during the growth of the plantation, only taking care to remove large weeds. This kind of tree culture, however, can only take place with advantage, on a tolerably level surface, where the soil is of the same nature throughout. Not to speak here of grounds destined for ornamental plan tations, the great majority of plantations formed with a view to profit are necessarily on hilly and unculturable surfaces, and where there is probably a variety of soil, even in a limited space. The preparation to be given in such cases is under-draining ; for to dig or trench the sur face would render it liable to be washed away by heavy rains and thawing snow. Plantations under such circum stances must be formed by digging pits for each tree, and by selecting such kinds as are best adapted to the locality. This frequently occasions the use of a variety of trees in the same plantation, causing a more picturesque effect in the landscape and a more advantageous result in the pro duction of timber. We have already stated that coniferous trees should be transplanted before they are four years old; but that broad-leaved trees may be moved at four, six, eight, or ten years growth ; provided they have been transplanted every two years in the nursery, and that the soil is sufficiently deep and moist to bring the fibrous roots into full action the first summer. When strong plants of this kind are used they overcome the natural herbage immediately; and, if carefully planted in good soil, not one in a score will fail. Smaller plants, on the other hand, are apt to be choked by herbage, and to have their leaves and young shoots injured by insects. In a dry soil and subsoil, plants with a mass of roots cannot subsist the first year ; and therefore smaller plants, once transplanted, are preferable. There are circumstances under which sowing is perhaps the only mode of forming plantations that can be adopted : as for example, in the dunes of Gascony, which by nearly a century of regularly continued sowings have been almost entirely transformed from drifting sandy wastes into forests of the cluster pine. In making planta tions of this pine we should prefer sowing several seeds in every place where a plant was intended to remain, unless we could procure a sufficient number of plants of two years old in pots. If more than one came up, the rest should be removed the second or third year ; and while the plants are young care must be taken that they are not choked by herbage. When steep rocky cliffs or stony hill-sides are to be covered with wood, sowing is the only mode that can be resorted to ; the kinds of seeds to be sown may be selected according to the nature of the debris or the soil in the clefts of the rocks. Where the soil is good, broad- leaved trees may be introduced ; but where it is poor, the Scotch fir, larch, birch, mountain ash, and white beam tree are most suitable. Where there is no visible soil, two or three seeds, enveloped in a composition of moss, cow-dung, and loam, may be deposited in crevices, or among loose stones ; acted upon by the rain, the seeds will vegetate, and find nourishment in the fragments of the ball in which they were enveloped. Two important points connected with the formation of plantations are the distances at which trees should be planted, and the use of nurse-trees. As the strength of a plant depends on the number of its leaves, and their full ex posure to light, it follows that the strongest young trees will be those which are clothed with branches and leaves from the ground upwards, and which have their leaves fully exposed on every side to light. The distance from each other at which trees should be placed in a plantation depends on the size and nature of the plants, and the soil, and situation. To Lave tall and straight stems, the trees are planted thickly (conifers more so than other kinds), about 4 to 6 feet apart; but when the lower branches of the plants interfere with one another, thinning should be commenced and con tinued from time to time. When the lower tier of branches shows symptoms of decay they should be removed by cutting close to the stem. This process of pruning has been condemned by many, particularly in soft-wood trees; but if practised early and judiciously it may be attended with benefit, especially when the part removed does not exceed an inch in diameter, or as long as the operation can be performed with an ordinary pocket-knife ; the wound will heal quickly, and leaves no mark. If branches are allowed to remain till they are 3 or 4 inches in diameter, and are then cut off at some distance from the bole (snag- pruning) the timber deteriorates, the wound heals over in time, but the timber is either knotty-or unsound. Close- pruning is performed by sawing off a branch close to the trunk or a leading branch. When the wound is large, a dressing should be applied to exclude air and moisture. For this purpose linseed oil, or three parts cow-dung and one part powdered lime, will be found useful. In the Royal Forests of England the branch of an oak is never removed unless special circumstances require it. Long experience has justified this system. Lateral branches which are growing with over luxuriance, and attracting too much of the sap of the plant, should be foreshortened, just as the lateral branches of a hedge are clipped when they extend too far. The only objection to this method of pruning is the amount of labour it entails. Mr M Nab of the Royal Botanic Garden, Edinburgh, has recently urged the advantage of stem-pruning of conifers, on the grounds that it encourages a free growth, and tends to make the trees hardy by exposing the bark of the stems to the freer action of the air. Stem-pruned trees also are less likely to be broken by a weight of snow lying on the branches. For pruning, the following tools are required,- a pocket knife, hand-saw, chisel, and pruning shears ; the two last are fixed on long poles. Thinning, carried out with care from time to time, is of the greatest consequence. The removal of weak and crooked supernumeraries prevents unnecessary exhaustion of the soil, while it admits the essential agents, air and light, which favour the expansion of lateral branches. If, however, the trees be thinned out too widely, the side branches become robust and the stem is not drawn up. The rule in thinning should be, to keep the trees clear of each other, so that the branches do not interlace, and the air circulates all round. The time when thinning should commence depends on local circumstances, and the species under cultivation. In a well-managed plantation the proceeds of thinnings in twenty years should go far to cover the expense of culture and interest of capital. The next point to be considered is that of introducing nurse-plants into plantations. That these have a tendency to accelerate the upward growth of trees for a number of years there can be no doubt, but it is at the expense of the side branches and leaves. Evergreen nurses, such as the Scotch, silver, and spruce firs, improve the condition of a plantation by preventing the radiation of heat from the ground, by checking the growth of herbage, and by pro tecting the principal trees from high winds until they are thoroughly established in the plantation. The kind of tree which is to form the main crop having been fixed on, and the number that when full grown will stand on an acre or any given surface, they should be planted in their proper places, and the intervals filled up with the nurse-plants. As the nurses grow, and their branches touch the princi pals, let them be thinned, so as not to prevent the free growth of the principals : this should be done gradually. For example, it is customary to pjant oak with coniferous

nurses, and in the course of seven to ten years the nurses