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larch
Значение термина larch в knolik
larch - Larch
larch - (Genus: Larix, Miller. Family: Abietaceae.) G. Lärche; F., Mélèze; W. Larsydden; E. Learog; American, Tamarack.
The larches are familiar to all country-dwellers, particularly in the early spring. Before March is out, they begin to unfold tassels of emerald green needles, amongst which are scattered the pink " Larch Roses or female flowers. The slender trunk tapers gracefully, and the pale branches stand out in gentle curves. The canopy of leaves overhead is always light and open, so that a Larchwood is open to the sun and air, and grasses and herbs clothe the ground beneath the tall trees. In October the needles turn to delicate yellow shades, for they last only one season; as winter advances, they drift down to cover the earth with a golden straw.
A spray of larch in leaf shows that the shoots are of two kinds. The only function of the " short-shoots which are merely round woody knobs, is to bear the deciduous needles year after year without elongating; each short-shoot is the centre of a tassel of needles. Elongation of trunk and branches is effected by the long- shoots, which also bear primary needles, arranged singly in spirals around them. In the axil of each primary needle is a tiny bud, which may remain dormant, or, during the following season when the branch which bears it is one year old, develop into a long or a short shoot. Primary needles sometimes persist on the tree after lading.
A peculiar feature of the larch, is that although the short-shoots spring into leaf so early in the year, the long-shoots seldom elongate until June or July; hence the larch has two leaf-flushes each season, as the primary leaves cannot appear until the shoot that bears them is elongating. The terminal buds are small and compact.
The bark of young larch stems is clothed in a delicate network of scales. As the stem expands and ages, these become less conspicuous and are gradually replaced by the characteristic flaky bark of the adult trunk, which in course of time becomes very thick and deeply fissured at the base of the tree. The trunk of the larch is always erect and seldom divided; it frequently assumes a slight' curve away from the wind. The crown is shallow, lacking depth because the lower branches cease to bear leaves when they are only slightly shaded by the younger branches above them.
Flowers are borne at an early age - about 20 years - and arise from the short-shoots in place of a tassel of leaves, at the same time of year or a little before them. The male flowers are small globular masses of stamens, bearing yellow pollen. The female flowers are more conspicuous, erect, oval bodies, rose-red in colour, borne near the tips of the long-shoots. After fertilisation, they enlarge and ripen in their first year into brown, oval, cones, short-stalked or sessile on the long-shoots. These are slow to open, and the winged seeds seldom fall before the dry weather of spring comes round, and in this way the risk of frost damage to the tender germinating seed is lessened. The empty cones, pretty structures of neat design, persist on the trees for some years.
The seedlings have many cotyledons, which are followed by a long-shoot bearing primary leaves. Short-shoots are seldom developed until the third or fourth year. Larch will regenerate itself naturally in Britain, but there are few localities where this is successful as a means of replacing the former crop. Most of the seedlings probably fall victims to late spring frosts.
The larches are essentially trees of high latitudes or high altitudes. The various species range round the north polar, regions and only extend southwards among the higher mountain ranges, such as the Alps and Himalayas. They are the trees of the roof of the world, and although we regard such regions as cold, during the vegetative season the heat may be great and the amount of radiation received from the sun is enormous. Thus, a larch tree in Siberia is in perpetual daylight for perhaps three months of the year, Whilst although the days in the Alps are not so long, the sun's rays have to strike through a thinner layer of atmosphere and are; correspondingly more powerful. Even more important to tree growth is the abrupt change from winter to summer found in such regions. The frost goes suddenly, and delicate foliage runs little risk from the late " spring " frosts which frequently occur in Britain in early summer.
The success of the larches in Britain is remarkable in view of these facts, which explain some of the failures which have occurred in our larch plantations. These failures are in no sense peculiar to Britain, as larch is similarly unreliable on the plains of central Europe. When a tree is brought to the edge of its possible environment, it becomes susceptible to many ills which do not trouble it greatly in its homeland. The importance of small differences in soil or situation is enhanced, since a very little variation upsets the delicate balance between the struggling tree and its surroundings. In the case of the larch, the biggest adverse factor is the Larch Canker (Dasyscypba), a fungal infection which follows any slight wound or break in the bark, deforming the stem and seriously weakening it, though it is seldom fatal.
Larch seed is obtained from cones, usually gathered from felled trees in winter. In the moist British climate these do not open easily, and it is usual to employ special crushing or tearing machinery to supplement the work of heat in seed extraction. Homegrown seed is much the best, since it derives from trees that have passed the acid test of thriving to their full rotation in the locality where it is desired to grow the future crop. Failing this, seed should be obtained from the lowest, or most southerly point in the natural range of the species. Very many of the failures of European Larch in this country are attributable to the use of high altitude seed from the Alps. The seed retains its germinative power for two or three years, and 80,000 grains go to the lb.
Larch seedbeds require overhead shade from late frosts; sun and drought are also harmful. Growth is rapid from the start, and the seedlings may be transplanted in their first year. For planting, a one-year-one-year or two-year-one year transplant about 15 inches high is best. The trees grow rapidly in their fourth year, and over that age are usually too big for forest planting.
The choice of sites for planting larches is restricted by several factors. They do not thrive on acid peaty soils where heather or heath is rampant. Waterlogged soils are unsuitable, but on the other hand so are sands which dry out in summer. They are fairly tolerant of lime, but cannot be expected to reach maturity on the shallower soils overlying chalk or limestone. Salt winds and industrial fumes affect them adversely, and they fall victims to spring frosts in low-lying hollows. Add to this the forester's rule- of-thumb that one crop of larch must not directly follow another, and it will be found that larch is restricted to fresh or alkaline soils, with a supply of moving moisture in summer, on ground which has previously been under another tree species or some herbaceous plant, such as bracken, which indicates fairly fertile soil. The best site is probably a hillside watered by springs. The larch transpires water rapidly during its short, intense, vegetative season; in its native haunts it is frequently watered by springs arising from the melting snows at higher levels.
Larches are strong light-demanders and cannot grow in shade. They are susceptible to late frosts, but are very wind-firm. Natural enemies, chiefly fungi, do great damage on unsuitable sites, but are not serious where the crop is growing under the right conditions. Larches are often planted in mixture with other conifers; in all such mixtures they must be given the light-demanding role, and the other partner is therefore usually a shade-bearer such as Spruce. One species, European Larch, will grow evenly when mixed with Scots Pine, and although both are light-demanders, they appear to help one another; other larches tend to outstrip the pines. Larches are frequently used as nurses for slower growing broadleaves, such as beech, ash or oak; they are cut out when from 15 to 20 years old, at which age they are readily saleable. Pure crops of larch are frequently under-planted with shade-bearers when they are from 30 to 40 years old, and have been thinned several times.
Thriving larch plantations make rapid growth, and frequent thinnings are necessary to prevent the young trees becoming too drawn-up. At every thinning, the crowns of the remaining trees must be left with ample room to expand. Thinnings are readily saleable from the smallest sizes for fence-rails, rustic poles and pickets, as they contain much heartwood and are durable out of doors. Larger sizes yield pitwood of the highest class, and still larger sizes provide excellent telegraph poles. Rotations for larch are fairly short, averaging around 80 years. It is not a long-lived tree, arid on many soils develops butt-rot at an early age. This means that the butts of the trees are useless as timber and must be discarded; as the butt is the most valuable portion of the trunk, it does not pay to leave the trees standing once the rot sets in. The decayed area lies in the centre of the trunk and is not revealed until the tree is felled. A height of 120 feet is frequently attained by larches, with girths up to 15 feet.
The timber of the larches has a red-brown heart with a pale yellow sapwood. The heartwood is resinous and durable, and the timber as a whole is very strong, and is highly valued for constructional work, particularly out of doors, commanding a higher price than other home-grown coniferous timbers. It is particularly useful for fencing, gates, and wooden buildings, bridges, boat building and railway sleepers. It has most of the advantages of a durable hardwood, together with the readier-working properties and lightness of a softwood or coniferous timber. Its rosy or rusty-brown colour and pronounced grain, give it an attractive appearance. The shape of the stem, with its slender branches, enable the whole tree to be converted to useful forms with a minimum of waste - less than with any other tree. The wood burns well, but is too valuable for use as firewood.
The European larch (Larix decidua, Miller) was introduced into Britain from the Alps in the sixteenth century, as an ornamental garden tree. Throughout the nineteenth century extensive plantations were established throughout Britain, and it retains its position as an important forest tree. Its distingufshing features are the green leaves, and straw-coloured twigs, with simple straight cone- scales. It is the most exacting of the larches with regard to soil and site, but it furnishes an interesting example of a tree, originally introduced for ornament only, becoming important forestally and economically.
The Japanese Larch (Larix kàmpferi, Sargent) or Karamatsu is distinguished by bluish-green needles, rosy-brown or russet twigs, and reflexed cone-scales, but otherwise resembles the European Larch very closely. Although it was only introduced to Europe in 1861, it has already become an important plantation tree, largely on account of its rapid growth. Coming from fairly low elevations in a maritime country, it takes more readily to British climatic conditions than does the European Larch. It is therefore successful over a wider range of soils and situations, and is less susceptible to fungal attack. Fig. 1e.
Its timber was regarded with great suspicion when first it became available, on the grounds that rapid growth must cause reduction in strength; but the latest evidence suggests that when a fair and sufficiently large sample of each timber is taken, it is nearly, if not quite, as good as European Larch wood.
Japanese Larch is variable in type, which suggests that local forms occur in its homeland. Probably certain of these are more' suited to British conditions than others. Leading shoots frequently develops spiral twist, but this is not a defect as it is soon obscured by the natural thickening of the trunk.
The Dunkeld Hybrid Larch (Larix eurolepis, A. Hénry) is a tree of recent British origin, arising from the chance cross-pollination of female Japanese Larch flowers by pollen from adjacent European Larch trees at Dunkeld, Perthshire. The first hybrid seedlings were raised in 1885, and trees of the second generation have since been planted. In appearance the hybrids are intermediate between both parents, but show great variability, some tending to follow either side. Their most notable feature is their extremely rapid growth, but this is not constant to all the trees of a batch, nor to every soil. The hybrid appears to need " fixation " of its most desirable characteristics by further scientific breeding, as is done with cultivated strains of wheat, though with trees it is a much longer process.
Seed and plants are scarce, but the hybrid will doubtless appear spontaneously amongst larches raised from home-grown seed collected wherever the two species are grown together. Its timber is still regarded with some suspicion on account of its rapid growth, but uses will probably be found for it as soon as it becomes available in useful quantities.
The larches of North America, Siberia, and the Himalayas have been grown as ornamental trees in Britain, but as they appear un- suited ^o the climate, have not been used for forest planting. Those of the Far East, in particular the Kurile, Dahurian, and Korean Larches from the neighbourhood of Japan, may be expected to grow more successfully in western Europe. The rarest of the Larches is a beautiful pendulous form, found only in cultivation and of uncertain natural origin. (L. pendula Salisbury, the Weeping Larch.)
The Golden Larch or Chin-lo-sung of China, is a rare and distinct tree classified in a separate genus and named Pseudolarix fortmei, Mayr. Its short shoots elongate slowly year by year, indicating how the fixed short-shoots of the Larix genus probably developed from long-shoots. The cones have angular, widely-set scales, which fall as the seeds ripen. The Golden Larch is valued for the tint of its autumn foliage, but is rare in cultivation.
Рядом со словом larch в knolik
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