Significations et usages de Birch

Birch
Silver Birch
Scientific classification
Kingdom:	Plantae
(unranked):	Angiosperms
(unranked):	Eudicots
(unranked):	Rosids
Order:	Fagales
Family:	Betulaceae
Genus:	Betula L.
Species
Many species; see text and classification

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Birch is a broadleaved deciduous hardwood tree of the genus Betula ( /ˈbɛtjʊlə/ Bé-tu-la),^[1] in the family Betulaceae which also includes alders, hazels and hornbeams and is closely related to the beech/oak family, Fagaceae. The genus Betula contains from 30 to 60 known taxa of which 11 are on the IUCN 2011 Red List of Threatened Species. They are typically rather short-lived pioneer species widespread in the Northern Hemisphere particularly in northern temperate and boreal climates.

  Etymology

The common name "birch" is derived from an old Germanic root, birka, with the Proto-Indo-European root *bherəg, "white, bright; to shine." The Proto-Germanic rune berkanan is named after the birch. The generic name Betula is from Latin.

  Description

  The front and rear sides of a piece of birch bark

Birch species are generally small to medium-sized trees or shrubs, mostly of temperate climates. The simple leaves are alternate, singly or doubly serrate, feather-veined, petiolate and stipulate. They often appear in pairs, but these pairs are really borne on spur-like, two-leaved, lateral branchlets.^[2] The fruit is a small samara, although the wings may be obscure in some species. They differ from the alders (Alnus, other genus in the family) in that the female catkins are not woody and disintegrate at maturity, falling apart to release the seeds, unlike the woody, cone-like female alder catkins.

The bark of all birches is characteristically marked with long, horizontal lenticels, and often separates into thin, papery plates, especially upon the paper birch. It is resistant to decay, due to the resinous oil it contains. Its decided color gives the common names gray, white, black, silver and yellow birch to different species.

The buds form early and are full grown by midsummer, all are lateral, no terminal bud is formed; the branch is prolonged by the upper lateral bud. The wood of all the species is close-grained with satiny texture and capable of taking a fine polish; its fuel value is fair.

  Flower and fruit

The flowers are monoecious, opening with or before the leaves and borne on three-flowered clusters in the axils of the scales of drooping or erect catkins or aments. Staminate aments are pendulous, clustered or solitary in the axils of the last leaves of the branch of the year or near the ends of the short lateral branchlets of the year. They form in early autumn and remain rigid during the winter. The scales of the staminate aments when mature are broadly ovate, rounded, yellow or orange color below the middle, dark chestnut brown at apex. Each scale bears two bractlets and three sterile flowers, each flower consisting of a sessile, membranaceous, usually two-lobed, calyx. Each calyx bears four short filaments with one-celled anthers or strictly, two filaments divided into two branches, each bearing a half-anther. Anther cells open longitudinally. The pistillate aments are erect or pendulous, solitary; terminal on the two-leaved lateral spur-like branchlets of the year. The pistillate scales are oblong-ovate, three-lobed, pale yellow green often tinged with red, becoming brown at maturity. These scales bear two or three fertile flowers, each flower consisting of a naked ovary. The ovary is compressed, two-celled, and crowned with two slender styles; the ovule is solitary.

  Ecology

  A stand of birch trees

Birches often form even-aged stands on light, well-drained, particularly acidic soils. They are regarded as pioneer species, rapidly colonising open ground especially in secondary successional sequences following a disturbance or fire. Birches are early tree species to establish in primary successions and can become a threat to heathland if the seedlings and saplings are not suppressed by grazing or periodic burning. Birches are generally lowland species, but some species, such as Betula nana, have a montane distribution. In the British Isles there is some difference between the environments of Betula pendula and Betula pubescens, and some hybridization, though both are "opportunists in steady-state woodland systems". Mycorrhizal fungi, including sheathing (ecto)myccorhizas, are found in some cases to be beneficial to tree growth.^[3]

Birch foliage is used as a food plant by the larvae of a large number of Lepidoptera (butterflies and moths) species; see List of Lepidoptera that feed on birches.

  Species

Birches native to Europe and Asia include

• Betula aetniensis—Sicilian birch
• Betula albosinensis—Chinese red birch
  • Betula albosinensis var. septentrionalis—north Chinese red birch
• Betula alnoides—alder-leaf birch
• Betula austrosinensis—South China birch
• Betula carpatica—Carpathian birch
• Betula chinensis—Chinese dwarf birch
• Betula dalecarlica
• Betula ermanii—Erman's birch
• Betula grossa—Japanese cherry birch
• Betula jacquemontii (Betula utilis subsp. jacquemontii)—white-barked Himalayan birch
• Betula kamtschatica—Kamchatka birch platyphylla
• Betula litvinovii
• Betula mandschurica—Manchurian birch
  • Betula mandschurica var. japonica—Japanese birch
• Betula maximowiczii—monarch birch
• Betula medwediewii—Caucasian birch
• Betula nana—dwarf birch (also in northern North America)
• Betula pendula—silver birch
• Betula platyphylla (Betula pendula var. platyphylla)—Siberian silver birch
• Betula pubescens—downy birch, also known as white, European white or hairy birch (Europe and northern Asia)
  • Betula pubescens subspecies tortuosa—arctic downy birch (subarctic Eurasia)
• Betula szechuanica (Betula pendula var. szechuanica)—Sichuan birch
• Betula tianshanica
• Betula utilis—Himalayan birch

Note: many American texts have B. pendula and B. pubescens confused, though they are distinct species with different chromosome numbers.

Birches native to North America include

• Betula alleghaniensis—yellow birch (B. lutea)
• Betula cordifolia—mountain paper birch
• Betula glandulosa—American dwarf birch
• Betula kenaica—Kenai birch
• Betula lenta—sweet birch, cherry birch, or black birch
  • Betula lenta subsp. uber—Virginia round-leaf birch (endemic, Cressy Creek, Smyth County, Virginia)
• Betula michauxii—Newfoundland dwarf birch
• Betula minor—dwarf white birch
• Betula nana—dwarf birch or bog birch (also in northern Europe and Asia)
• Betula neoalaskana—Alaska birch or Yukon birch
• Betula nigra—river birch or black birch
• Betula occidentalis—water birch or red birch (B. fontinalis)
• Betula papyrifera—paper birch, canoe birch or American white birch
• Betula populifolia—gray birch
• Betula pumila—swamp birch

  Uses

  Birch plywood

• Birch wood is fine-grained and pale in colour, often with an attractive satin-like sheen. Ripple figuring may occur, increasing the value of the timber for veneer and furniture-making. The highly decorative Masur (or Karelian) birch, from Betula verrucosa var. carelica, has ripple textures combined with attractive dark streaks and lines. Birch wood is suitable for veneer, and birch plywood is among the strongest and most dimensionally stable plywoods, although it is unsuitable for exterior use.
• Birch plywood is made from laminations of birch veneer. It is light but strong, and has many other good properties. Birch plywood is used to make longboards (skateboard), giving it a strong yet flexible ride. It is also used (often in very thin grades with many laminations) for making model aircraft.
• Extracts of birch are used for flavoring or leather oil, and in cosmetics such as soap or shampoo. In the past, commercial oil of wintergreen (methyl salicylate) was made from the sweet birch (Betula lenta).
• Birch-tar or Russian oil extracted from birch bark is thermoplastic and waterproof; it was used as a glue on, for example, arrows, and also for medicinal purposes.^[4]
• Fragrant twigs of silver birch are used in saunas to relax the muscles.

  Birch leaves

• Birch is also associated with the feast of Pentecost in Germany, Central and Eastern Europe, and Russia, where its branches are used as decoration for churches and homes on this day.
• Birch leaves are used to make a diuretic tea and extracts for dyes and cosmetics.
• Ground birch bark, fermented in sea water, is used for seasoning the woolen, hemp or linen sails and hemp rope of traditional Norwegian boats.
• Birch twigs bound in a bundle, also called birch, were used for birching, a form of corporal punishment.
• Many of the First Nations of North America prized the birch for its bark, which due to its light weight, flexibility, and the ease with which it could be stripped from fallen trees, was often used for the construction of strong, waterproof but lightweight canoes, bowls, and wigwams.
• The Hughes H-4 Hercules was made mostly of birch wood, despite its better-known moniker, "The Spruce Goose".
• Birch is used as firewood due to its high calorific value per unit weight and unit volume. It burns well, without popping, even when frozen and freshly hewn. The bark will burn very well even when wet because of the oils it contains. With care, it can be split into very thin sheets that will ignite from even the smallest of sparks.
• Birch sap is a traditional drink in Northern Europe, Russia, and Northern China. The sap is also bottled and sold commercially. In the British Isles, the sap is often used to make a wine.^[5]
• Birch seeds are used as leaf litter in miniature terrain models.^[6]
• "Birch flowers" is the English marketing name for the catkins of the Broussonetia luzonica tree. Known in the Philippines as himbabao or alukon, these flowers are commonly used in the cuisine of northeastern Luzon. However, despite their English name and the similar appearance of their flowers, B. luzonica is not in any way related to the birch tree.^[7]

  Medical

• Birch bark is high in betulin and betulinic acid, phytochemicals which have potential as pharmaceuticals, and other chemicals which show promise as industrial lubricants.^{[citation needed]}
• Birch bark can be soaked until moist in water, and then formed into a cast for a broken arm.^[8]
• The inner bark of birch can be ingested safely.
• In northern latitudes, birch is considered to be the most important allergenic tree pollen, with an estimated 15-20% of hay fever sufferers sensitive to birch pollen grains. The major allergen is a protein called Bet v I.

  Paper

  A birch bark inscription excavated from Novgorod, circa 1240–1260

Wood pulp made from birch gives relatively long and slender fibres for a hardwood. The thin walls cause the fibre to collapse upon drying, giving a paper with low bulk and low opacity. The birch fibres are, however, easily fibrillated and give about 75 % of the tensile strength of softwood.^[9] The low opacity makes it suitable for making glassine.

In India, the birch (Sanskrit: भुर्ज, bhurj) holds great historical significance in the culture of North India, where the thin bark coming off in winter was extensively used as writing paper. Birch paper (Sanskrit: भुर्ज पत्र, bhurj pətrə) is exceptionally durable and was the material used for many ancient Indian texts.^[10][11] This bark also has been used widely in ancient Russia as note paper (beresta) and for decorative purposes and even making footwear.

  Tonewood

Baltic birch is among the most sought-after wood in the manufacture of speaker cabinets. Birch has a natural resonance that peaks in the high and low frequencies, which are also the hardest for speakers to reproduce. This resonance compensates for the roll-off of low and high frequencies in the speakers, and evens the tone. Birch is known for having "natural EQ".

Drums are often made from birch. Prior to the 1970s, it was one of the most popular drum woods. Because of the need for greater volume and midrange clarity, drums were made almost entirely from maple until recently, when advances in live sound reinforcement and drum microphones have allowed the use of birch in high-volume situations. Birch drums have a natural boost in the high and low frequencies, which allows the drums to sound fuller.

Birch wood is sometimes used as a tonewood for semiacoustic and acoustic guitar bodies, and occasionally for solid-body guitar bodies. It is also a common material used in mallets for keyboard percussion.

  Culture

• Birches have spiritual importance in several religions, both modern and historical.
• They are associated with the Tír na nÓg, the land of the dead and the Sidhe, in Gaelic folklore, and as such frequently appear in Scottish, Irish, and English folksongs and ballads in association with death, or fairies, or returning from the grave.
• It is also New Hampshire's state tree.
• In the Swedish city of Umeå, the silver birch tree has a special place. In 1888, the city was ravaged by fires that spread all over the city and nearly burnt it down to the ground, but some birches, supposedly, halted the spread of the fire. To protect the city against future fires, it was decided to plant silver birch trees all over the city. Umeå later adopted the unofficial name of "City of the Birches (Björkarnas stad)". Also, the ice hockey team of Umeå is called Björklöven, translated to English "The Birch Leaves".
• In parts of Germany, young men erect decorated birch trees in front of the houses of their love interests on the night of May 1, to show their feelings.

  See also

Trees portal

• Birch beer
• Taxonomy of Betula

  References

• Flora of North America: Betula
• Flora of China: Betula
• Grimshaw, John (2009). New Trees, Recent introductions to cultivation. Kew Publishing, RBG Kew. pp. 163–174. 

  External links

Wikimedia Commons has media related to: Betula

Wikispecies has information related to: Betula

• Tree Family Betulaceae Diagnostic photos of many species, Morton Arboretum specimens