birch defined in 1944 yearbirch - Birch;
birch - G. Birke; F. Bouleau; W. Bedwen; E. Beit; A.-S. Birce;
The slender paper-white trunk of the birch, together with the fine meshwork of the dark branches ending in still finer pendulous twigs, gives the Silver Birch an air of delicacy unrivalled by any other tree. The winter twigs are distinctive, thin and whiplike, dark brown or black in colour; with prominent hard warty growths. The tiny buds are spirally placed. The bark of the trunk is quite distinct from that of the branches, as it develops by the shedding of outer layers to a smooth white surface with thin black horizontal lines of lenticels. From time to time it peels away in horizontal bands a few inches broad; at the base of old trees a rugged black bark may eventually supersede the white one.
The leaves of the birch appear in April, and are small, about half an inch long, simple, serrated-edged, and varying in outline from triangular through rhombic to oval. They are grey-green in colour and, being lightly poised on their stalks, are easily stirred by the wind. They turn yellow before falling in October.
The flowers appear in early April, just as the leaves open, and are grouped in catkins. Both male and female catkins are borne on the same tree, the male being conspicuous, pendulous, a little more than an inch long and resembling in shape a lamb's tail; each catkin scale shields twelve stamens. The female catkins are smaller, more erect, and less conspicuous, each scale protecting three flowers. After fertilisation, these catkins enlarge, elongate, and become pendulous. In September they begin to break up, the scales falling away to release three tiny winged nutlets. Pollination and the distribution of seed are effected by wind. Seed is plentiful in most seasons.
The birch occurs throughout Britain on all but the poorest and wettest of soils. It is at its best on old woodland areas, and avoids the more acid heather peats. Natural regeneration is excellent wherever protection is afforded against grazing animals, though it is not a palatable tree and is only resorted to when other feed is scarce.
A second British species, Betula pubescens Ehrh., is distinguished mainly by downy twigs which lack die warts of the type, but hybrids and intermediate forms occur. B. pubescens is the more northerly form. A third distinct species, Betula nana L., the Dwarf Birch, a shrub only a few feet high, occurs in Scotland as a relic of the vanishing alpine flora of the Ice Age.
The Silver Birch has a wide distribution throughout Europe and northern Asia, and allied species are found in Japan, the Himalayas, and North America. Certain of these are cultivated in Britain.
The seed of birch should be collected just before the catkins break up; it is simplest to remove small branches, place them in sacks, and hang them up to dry. The seed will then fall away into the sacks, and may either be sown at once, or stored in moist sand until early spring. About 700,000 seeds go to the pound, but only a small proportion, about one-fifth, will germinate under the best of conditions, and the seed does not stand prolonged storage. It must be sown thinly and covered lightly.
The two tiny oval cotyledons which the birch seedling thrusts above the ground are followed by normal leaves, and early growth is rapid. After one year in the seedbeds and a second in transplant lines, the young trees should be over a foot high and fit for forest planting.
Birch is seldom used to form plantations, being mainly in demand for fire-breaks or as a nurse to more tender and valuable species. Its leaves form a valuable humus. It is extremely light-demanding, and given full sun is not particular as to soil or site. It is frost- hardy and wind-firm. When used as a nurse, whether it be of natural or artificial origin, birch must be carefully kept in check or its rapid growth will cause it to overtop most other species. Birch has few natural enemies, and thrives reasonably well in urban areas.
If felled young, birch will coppice, but the resulting shoots are small, crooked, and valueless. It reaches maturity at an early age, being about 60 feet tall after 50 years, after which height growth ceases; it is reputed to be a short-lived tree, but will stand for at least 80 years on good sites. Its growth under British conditions is seldom straight enough to provide first-rate timber, but in Scandinavia it is of great value, when straight and close-grown, for the manufacture of plywood veneer, which is peeled off by rotating the log against a knife. Heights up to 85 feet are occasionally reached.
The wood is pale brown in colour, and has no distinct heart. Out of doors it is so perishable as to be useless, but when kept dry its mechanical properties are good. It is frequently converted by turning, to make bobbins, bungs, bowls, brushes, toys, and countless similar small articles. It is a good firewood, and may be used for charcoal. Large girths are unknown; 6 feet is the maximum.
The bare twigs of birch can be made up into useful brooms for yard or garden. If tied rather more compactly than usual, such brooms make excellent beaters for beating out heath and forest fires. The bark of American species, being waterproof, is used for the skin of portable canoes.
Except as an ornamental tree, birch has been very little cultivated in Britain, and most birch groves are of natural origin. Its rapid growth should make its cultivation profitable, but as conifers thrive equally well on most sites suited to it, birch is seldom planted. Natural birch groves are seen in Figs. 4 and 5.
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near birch in Knolik
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