pine defined in 1944 yearpine - Pine;
pine - (Genus: Pinus L. Family: Abietaceae.)
The true pines are the most important group of the conifers, with at least seventy species and many minor varieties, distributed throughout the northern temperate and sub-tropical zones. All are readily distinguished by their peculiar " short-shoots," which take the form of a short sheath holding a group of needles. The number of needles in each sheath is normally fixed for each species, and aids in identification. But it is not a fundamental factor distinguishing groups of species, and one species is known, from Mexico (P. cembroides, Zucc.), which may have one, two, three, four, or five needles per sheath, all on one branch.. These obvious needles of the Pines are secondary leaves; the primary leaves are inconspicuous brown scales at the base of the sheath-like short-shoots. Seedling pines, however, have fully developed green primary needles, placed spirally on the young shoot. Both types of leaves are evergreen, but their life is short and they fade and fall after a few vegetative seasons; usually the sheath and its group of needles fall together.
In their manner of branching the pines follow the rigid pattern of other conifers throughout their youth, but when nearing maturity many species develop strong, irregular side branches or subsidiary leaders, producing crowns similar to those of broadleaved trees. The bark varies with the species, but is usually very thick, scaly, and deeply fissured.
The flowers of the pines appear at the early age of 1,5 years or less. The male flowers are globular bodies borne in groups near the base of young shoots of the current year, taking the place of short-shoots. They consist of numerous anthers, and in spring are made -conspicuous by masses of golden pollen. The female flowers are red or green globular bodies, on a short stalk, and always appear in the same position, bright at the tips of the branches to one side of each branch's main axis, taking the place of a side bud which would otherwise develop into a long-shoot. They open as soon as the annual elongation of the long-shoot which bears them is completed, about June. Pollination is by wind, but the cones remain small and undeveloped until the following spring. Then they develop rapidly, becoming bright green in colour. By the following autumn, the seed within them ripens, and they turn brown. They do not open until the next spring - two years after fertilisation, and then in most species they release small winged seeds; in a few species they remain closed and the seeds cannot grow until the cone falls and rots away. As the old, and usually empty, cones persist on the trees, it is possible to find cones in four stages of growth on the same tree in late spring, as follows: (1) opening female flower of the current season; (2) closed, developing cone, one year old; (3) opening ripe cone, shedding seeds, 2 years old; (4) empty, open cone, 3 years old. A distinctive feature of the genus is the thick, woody, and sometimes sharp thickened area at the tip of each cone-scale, termed the "umbo".
Seedlings of pines have many cotyledons, followed during the first year by a single erect shoot with long primary needles, at this stage they are hard to distinguish from seedlings of many other conifers. These primary leaves may be borne on the leader for two or three seasons, varying with the individual plant. They sometimes appear on the side shoots of seedlings, and occasionally on new branches which emerge from an inter- node when the leading shoot is cut back or injured. On the normal branches, they are represented by short brown deciduous scales beneath each short-shoot.
The normal annual growth of a young pine tree (out of the seedling stage) proceeds as follows: At the tip of the leading shoot, a stout terminal bud is to be found during the winter months, surrounded by a variable number of side buds (frequently 4). About April, this terminal bud starts to grow, casting off its scales and elongating upwards into a long-shoot. As it extends, the short- shoots which were concealed within it, also develop, so that when growth ceases about July, the year's shoot-growth (or internode) is clothed in an array of secondary needles. Then a new terminal bud, with its quota of laterals, is formed at the tip of the spring growth, ready for the next season. In the meantime, the lateral buds have been elongating outwards in similar fashion, in several directions, extending the foliage of the tree regularly in proportion to its height growth. Exceptionally, two internodes are grown in one season.
The remarkable feature of this mode of growth is the sudden appearance of developing short-shoots on a still immature long- shoot. All the obvious growth occurs in spring, when shoot- length and foliage appear rapidly and simultaneously. Then comes a period of summer rest, when reserves are built up for the next year's intense outburst of growth, followed by the dormant period of winter.
Cones for seed are collected in winter from fellings or standing trees, care being taken to gather only unopened cones one node back from the tips of the branches. These cones, from 18 months to 2 years old, contain fertile seeds which can be seen by splitting them through longitudinally. After drying, these cones open readily in sunshine or mild heat, releasing winged seeds from which the wings may be detached by rubbing or light rolling; the light wings are easily winnowed or blown away. The resistant cones of some species require stronger heat or crushing before the seeds are freed. The seeds vary greatly in size; they retain their germinative power for two or three years.
In the seedbeds, germination is rapid and the seedlings need little or no protection from sun or frost. They may be transplanted when 1 or 2 years old - after that they grow very fast, needing only 1 or 2 years in the transplant lines. On bare ground where there is little ground vegetation to compete with, one-year-one plants may be used. Elsewhere, three-year-old plants, either one-year- twos or two-year-ones, give the best results. Two-year-twos are satisfactory, but trees over 4 years old are too big for forest work. Trees that have stood for 3 years in beds or lines without a break, develop unevenly and should be avoided. Direct planting with seedlings, usually 2 years old, is sometimes done successfully, and may be advisable for some species difficult to transplant. Direct sowing is also practicable, but a great deal of seed is required which could be employed to much better advantage in the nursery than in the forest. Natural regeneration is successful with certain species under the right conditions.
All the pines are light-demanding trees, usually quick-growing and wind-firm, on account of their branched root system which spreads both wide and deep. They prefer well-drained soils, but the species have varied requirements regarding climate and soil conditions. Rotations of pure crops are usually short - from 60 to 100 years. Young trees must be left with plenty of room when thinning; they are easily suppressed and killed out by lack of sunlight. Besides their use in pure plantations, pines are greatly valued as nurses for other coniferous and broad-leaved trees, and as shelter- belts, and frequently form an important part of mixed plantations. Their rapid growth in youth enables them to take the brunt of the wind on exposed sites. They are naturally " pioneer " trees, able to colonise bare ground as the first tree species. Their demands on soil fertility are slight, they will grow on raw sand or gravel; but naturally the best growth is found on more loamy and developed soils. They have great resistance to drought, and many species withstand both intense winter cold and late spring frosts.
The timber of pines is resinous, with a well-developed heart, but is not naturally durable out of doors, though it is used in enormous quantities for all types of constructional work where it can be kept dry or treated with preservatives, and it provides much of the world's building timber.
Natural pine forests occupy a substantial proportion of the earth's land surface. As their reserves are diminished by the felling of the older virgin stands, the importance of the plantation pinewoods increases. In Britain we have one native species - perhaps our most important timber tree, and at least one imported species has already assumed economic importance. Other new species are undergoing trial, both here and on the continent of Europe.
The world distribution of the many species of pines is wide and interesting. Besides the Scots Pine, which forms the subject of a separate chapter, there are many 2-needled and two 5-needled species occurring naturally in Europe, and extending their range in some cases to Asia Minor and North Africa. Important species occur throughout the Himalayas, in China, Japan and Siberia. They penetrate southwards down the mountain chains to Burma, and are found in the Philippine Islands and the East Indies, where they thrive on the cool highlands of Sumatra and Malaya.
Throughout North America, pines of various species constitute an important element of the forest flora. They extend southwards to California, Mexico and Central America. Isolated island races occur in the Canary Islands and the Bahamas, indicating the great antiquity of the genus.
Pines do not occur naturally in the southern hemisphere, but on introduction to South Africa, Australia, and New Zealand have thriven remarkably well and already produced valuable timber crops. As introduced trees, removed to a more favourable environment, the pines are making a remarkable showing; in a state of nature they tend to be restricted to unfavourable habitats by the competition of other trees and plants, besides animals and man.
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