Arboriculture, a term literally signifying the cultivation of trees, is in use generally restricted to the planting and management of timber trees, exclusive of the cultivation of fruit trees, which is a branch of horticulture or gardening.
The ancients practised arboriculture to some extent, but chiefly with the view of beautifying their villas, or of forming public walks in the vicinity of cities. The planting of timber trees for economical purposes, or with a view to profit, is unnecessary whilst natural forests are abundant, and can scarcely be referred, even in Britain, to an earlier period than the beginning of the 16th century, nor did it become general till a much later date. The early forest laws of England, as of other feudal countries, had reference chiefly to game, for the sake of which large tracts were depopulated and converted into forests by the first Norman kings. Plantations for timber and fuel were, however, made in England in the 16th century; and the importance of the subject was urged on public attention by authors of that period. In the 17th century, the greatly increased demand for oak, for the building both of ships and of houses, gave a new impulse to arboriculture, which attracted the attention at once of the government and of the great landowners: the publication of Evelyn's Sylva also rendered an important service in promoting a taste for it; and the next great work was Loudon's. Nurseries for forest trees were first established in this century. It was not until the beginning of the 18th century that the first extensive plantations were made in Scotland, nor until towards the end of that century that arboriculture became general in that country or in Ireland. How much the landscape has been changed by the introduction of foreign trees, it is not easy to imagine; and how much these changes have promoted and are indicative of improvements in agriculture and increased productiveness of land, is difficult to estimate.
In Britain, arboriculture, or the planting and tending of single trees, has been better understood than sylviculture, or the reproduction by seed and training of natural forests. In France and Germany, attention has long been paid to sylviculture by conserving the indigenous woods. Without systematic management of these tracts, many districts of these countries would soon be destitute of fuel, and by means of it an increased supply of timber is obtained, and extensive domains belonging to the state or to private proprietors are rendered more productive.
The forest trees of Britain, and of temperate climates generally, are conveniently divided into two classes—the one consisting of coniferous trees, or pines and firs (Nadelholz—i.e. the ‘needlewood’ of the Germans), the other including all other kinds (Laubholz—i.e. the ‘leaf-wood’ of the Germans); the latter being sometimes subdivided into hard-wooded trees, of which the most important in Britain are oak, ash, elm, beech, birch, hornbeam, sycamore, walnut, and chestnut; and soft-wooded trees, as willow, poplar, lime, and horse-chestnut. Of these and other trees, of their particular uses, and of the soils and situations to which they are adapted, notice is taken in separate articles.
Plantations are generally formed in Britain by means of seedlings raised in a nursery; but sometimes also by sowing the seed on the ground intended for the plantation; in which case, a crop of grain is often sown along with the seeds of the trees, as these do not in general vegetate very soon; and the young plants derive advantage from the absence of weeds when the grain-crop is reaped, and from the protection afforded by the stubble. However, only very small trees can be planted with advantage, those which have attained a greater size requiring more attention than is possible in plantations even of moderate extent. The time of planting is in spring or autumn. The most approved mode of planting is in small pits, in which the roots are disposed in a natural manner, and which are then carefully filled up with earth; but it is often sufficient, when the seedling to be planted is very young, to make a slit for it with the spade, or two slits, one at right angles to the other in the form of the letter T. Other methods are adopted, particularly for rocky situations, in which the spade cannot be used. Economy is a consideration of great importance in determining the mode of planting.
The formation of plantations by the sowing of seed is more generally practised on the Continent than in Britain. In this way the vacancies in the natural forests of France and Germany are filled up, and great sandy tracts have been covered with wood on the coasts of Denmark, Prussia, and France. This has been accomplished on a scale of extraordinary magnitude in the dunes of drifting sand, between the rivers Adour and Gironde. The operations begun by M. Bremontier in 1789 deserve to be mentioned, as perhaps the most important operations in arboriculture that have been performed in the world. Vast forests of pinaster now occupy what was originally loose sand destitute of vegetation. In recent times, the planting of teak, cinchona, sandalwood, eucalyptus, and deodar, by the Forest Department in India, is a work of great utility, and has already been a financial success.
Too little attention has been paid to the adaptation of the kinds of trees that are planted to the soil and climate; and to this cause many failures in arboriculture may be ascribed. Some trees grow well even in exposed situations, and are fit to be employed either to form entire plantations, or to occupy the outer part, and so to shelter other trees, which in general are not planted until the outer zone or belt of the most hardy kinds is somewhat advanced; some succeed only in rich soils; some are incapable of enduring the sea-breeze; others, as the sycamore, the elder, and the pinaster, are comparatively unaffected by it. Some trees suffer from an amount of moisture from which alders or willows would rather derive advantage; but, in general, the thorough drainage of the land intended for a plantation is important to its success.
We must look to the necessity of drainage, especially of marshy soils, as compensating the influence which woods exercise in condensing the moisture of the atmosphere, and in rendering a climate cold and damp. The shelter afforded by plantations judiciously disposed, whether in belts or otherwise, is also of great importance in rendering soils suitable for that improved agriculture in which thorough drainage is of the first necessity, and which is always productive of amelioration of climate. The influence of plantations is therefore beneficial, although vast masses of forest are injurious to climate; and it must be admitted that in some localities the planting of trees has been carried to excess, so that fields often suffer, particularly in autumn, from want of free circulation of air.
Much has been written about the pruning of forest trees, with a view especially to the production of taller and straighter stems; and considerable difference of opinion exists as to the extent to which pruning should be practised. It is, however, generally delayed till the branches to be removed have attained too great a size, and is then rudely performed, to the spoiling of the timber rather than to the improvement of it. The practice of leaving snags, instead of cutting branches clean off, has injurious effects. Pines and firs, from their manner of growth, need pruning less than trees of other kinds. When trees have been planted, not for profit but for ornament, this ought to be remembered in pruning, which, however, is often intrusted to persons utterly devoid of taste; and trees which were very beautiful in nature, are so treated with axe and saw that they become unsightly deformities.
In forming plantations, different kinds of trees are generally mixed, although masses of one particular kind are also frequently planted. It is usual, however, to plant along with those which are destined permanently to occupy the ground, trees of other kinds as nurses, to be gradually removed as the plantation advances in growth. For this purpose, spruce and larch are generally employed; although Scotch fir and birch are also deemed suitable for certain situations. The removal of some of these nurses affords the first return of profit from the plantation, which is afterwards thinned from time to time. Plantations more frequently suffer from being thinned too little, than from being thinned too much. To the want of proper thinning is to be ascribed the failure of many of those narrow belts of planting which are too common in Scotland, and which, having been intended for shelter, serve their purpose but imperfectly, and seem to have suffered from maltreatment. The thinning of a plantation which has been allowed to grow too thick, must, however, be gradually performed, that it may be beneficial and not injurious. After a sudden thinning, a plantation sometimes ceases to thrive, and many trees are laid prostrate by the next storm; for trees accommodate themselves both in their roots and branches to the situations in which they grow.
A considerable number of years must elapse before any pecuniary return is derived from a plantation, yet the planting of unculturable land is often found to be the most remunerative of which they are capable, even without reference to the improvement of adjacent lands to which shelter is afforded. The resinous products of pine-woods are not considered as a source of profit in Britain; but the tar, turpentine, and resin obtained from them in some parts of Europe form articles of commerce.
The wholesale destruction of forests in the United States brought about serious evils; and of late, measures have been taken, both by public autho- rities and private persons, for cherishing existing trees and woods, and for planting extensively where the ground is bare of timber. In some of the western states especially, where the need of shelter for horses, crops, and cattle has been found in increasing measure, the movement is now carried on on a very large scale, trees being planted by millions annually.
The employment of trees for ornamental purposes belongs not so much to arboriculture as to Landscape Gardening (q.v.). The Transplanting (q.v.) of large trees is only practised for ornamental purposes. Hedgerow trees are planted chiefly for ornament, although sometimes they afford useful shelter; but where this is not the case, they can seldom be reckoned profitable, as they are injurious to crops. Copse (q.v.) or copse-wood differs much, both in its uses and in the mode of its management, from other plantations.
There is a great school of forestry at Nancy, to which English students used largely to resort; and Germany and most European countries have special forestry schools. The Forestry Exhibition at Edinburgh in 1884 created some popular interest on the subject. In 1887, a committee appointed by the House of Commons recommended the establishment of a Forestry Board and national school in England.
Certificates in forestry are granted by the Highland and Agricultural Society of Scotland, whose Transactions contain valuable papers on arboriculture; and at the Indian Engineering College, Cooper's Hill, Staines, a course of two years' training is arranged for forest candidates preparing for the Indian Forest Department.
See various works on Arboriculture or Silviculture, by J. Croumbie Brown (1875-87), Grigor (1881), Bagneris (trans. 1882), Schlich (1889-91), Nisbet (1893), and Fürst (1893).