Arboriculture

Arboriculture, though etymologically including everything relating to the culture of trees, may, as opposed to sylviculture, be limited to the management of trees artificially planted in nurseries and plantations, and, as opposed to certain branches of horticulture and landscape gardening, be further restricted to the cultivation of timber and other trees for purposes of profit. In the selection of a site for a plantation and of the trees suitable for the same, consideration must be paid to the effects of climate and soil, the physiological requirements and peculiarities of the various species, and the market for the produce. An insular climate, moist and free from frost, is suitable for many broad-leaved evergreens; a continental one with hot summers and cold winters produces well-matured timber from broad-leaved deciduous trees; and conifers (needle-leaved trees, mostly evergreen) as a class will grow well and to full size, speaking generally, in higher latitudes than other trees. Though trees will not grow in a rainless tract, their presence will render any rainfall more uniform and apparently slightly increase the amount. Birch, Scots, Austrian and cluster pine will flourish in very dry, sandy soil, and other species, such as the beech and holly, prefer a warm soil, i.e. one with thorough drainage; but oak, elm, larch, and spruce do better in colder, less permeable soils, such as loams or clays, so long as they do not actually retain stagnant water. The deciduous cypress (Taxodium distichum) and many poplars, willows, and alders will flourish in actually swampy ground. It may be remembered that the fine timber of the Baltic provinces, though matured by extreme winter cold, grows for months at a time in some depth of standing water. A rich soil, like a moist climate, though conducive to rapidity of growth, produces spongy, less durable timber. The Oregon pine grows more rapidly in Scotland than in the Rocky Mountains; but the wood formed is not as valuable. Of European timbers the strongest and most durable is oak; but the conifers being far more rapid in growth yield a quicker return to capital invested in planting. In poor soil the Scots fir is, therefore, much grown in Britain; but in slightly better soil the more durable and yet quicker growing larch is preferred. Possibly the Oregon pine may prove a formidable rival to both. Nothing was done in England in the way of tree-planting before the 16th century, and although Evelyn's Sylva had an undoubtedly beneficial effect in kindling a taste for arboriculture, it was not until the 18th century, when large plantations were made, that any serious attention was given to the subject.

To secure even results it is better to form a plantation by planting trees than by sowing. This involves the maintenance of nurseries. Nurseries should be on high ground, but little exposed to frost, with a friable soil, free from stones, well-drained and containing vegetable matter, but unmanured. Both climate and soil, though such as to secure germination of seeds, should, to furnish hardy trees, be inferior to those of the plantation. Timber trees are mostly raised from seed, and this should be collected when well ripened. Fleshy fruits, such as holly and hawthorn, may be kept till the second spring, and those of most other trees until the spring immediately following their ripening. Poplar and willow are commonly raised from cuttings; but if grown from seed it should be sown directly it is ripe. In the spring of their second year it is usual to cut off the tap-roots of most young trees with a spade so as to force them so send out lateral roots and to facilitate transplantation. Nursery plants should be transplanted every two years. Conifers may be planted out before they are four years old; broad-leaved trees at four, six, eight or ten years of age. On steep or stony hillsides sowing may be the only method of planting possible; but elsewhere the ground should be prepared beforehand, drained if necessary and freed from weeds. In planting largish trees it is well to prepare a pit for each before the winter preceding planting. In all cases weeds should constantly be removed until the branches of the trees fairly overshadow the ground. Trees should be planted from four feet apart (2,722 per acre) in the case of conifers, to six feet (1,210 per acre) or even farther. To accelerate the upward growth of the trees "nurses," such as quick-growing evergreen firs, are often planted between broad-leaved trees protecting them from wind and drought and checking weeds. In from seven to ten years the branches of these nurses will touch the more valuable trees, and periodical thinning should then be at once commenced. The thinnings will in this way be of some value as poles, etc., from the first. In thinning, any weak, malformed or unhealthy trees should be removed; but it is important, if long timber is desired, that the trees be not too much thinned, or side branches will be produced rather than length of stem. The rule should be to thin sufficiently to prevent interlacing of branches until the next rotation.