Birch
A birch is a thin-leaved deciduous hardwood tree of the genus Betula, in the family Betulaceae, which also includes alders, hazels, and hornbeams. It is closely related to the beech-oak family Fagaceae. The genus Betula contains 30 to 60 known taxa of which 11 are on the IUCN 2011 Red List of Threatened Species. They are typically short-lived pioneer species and are widespread in the Northern Hemisphere, particularly in northern areas of temperate climates and in boreal climates. Birch wood is used for a wide range of purposes.
Description
Birch species are generally small to medium-sized trees or shrubs, mostly of northern temperate and boreal 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. The fruit is a small samara, although the wings may be obscure in some species. They differ from the alders 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. Distinctive colors give the common names gray, white, black, silver and yellow birch to different species.
The buds, forming early and full-grown by midsummer, are all lateral, without a terminal bud forming; the branch is prolonged by the upper lateral bud. The wood of all the species is close-grained with a satiny texture and capable of taking a fine polish; its fuel value is fair.
Flower and fruit
The flowers are monoecious, and open with or before the leaves. Once fully grown, these leaves are usually long on three-flowered clusters in the axils of the scales of drooping or erect catkins or aments. Staminate catkins 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 mature staminate catkins are broadly ovate, rounded, yellow or orange colour below the middle and dark chestnut brown at apex. Each scale bears two bractlets and three sterile flowers, each flower consisting of a sessile, membranous, 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 segments are erect or pendulous, and 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. Each scale bears a single small, winged nut that is oval, with two persistent stigmas at the apex.Taxonomy
Subdivision
Betula species are organised into five subgenera.; Birches native to Eurasia include
- Betula albosinensis – Chinese red birch
- Betula alnoides – alder-leaf birch
- Betula ashburneri –
- Betula baschkirica –
- Betula bomiensis –
- Betula browicziana –
- Betula buggsii –
- Betula calcicola –
- Betula celtiberica –
- Betula chichibuensis –
- Betula chinensis – Chinese dwarf birch
- Betula coriaceifolia –
- Betula corylifolia –
- Betula costata –
- Betula cylindrostachya –
- Betula dahurica –
- Betula delavayi –
- Betula ermanii – Erman's birch
- Betula falcata –
- Betula fargesii –
- Betula fruticosa –
- Betula globispica –
- Betula gmelinii –
- Betula grossa – Japanese cherry birch
- Betula gynoterminalis –
- Betula honanensis –
- Betula humilis or Betula kamtschatica – Kamchatka birch platyphylla
- Betula insignis –
- Betula karagandensis –
- Betula klokovii –
- Betula kotulae –
- Betula luminifera –
- Betula maximowicziana – monarch birch
- Betula medwediewii – Caucasian birch
- Betula megrelica –
- Betula microphylla –
- Betula nana – dwarf birch )
- Betula pendula – silver birch
- Betula platyphylla – —Siberian silver birch
- Betula potamophila –
- Betula potaninii –
- Betula psammophila –
- Betula pubescens – downy birch, also known as white, European white or hairy birch
- Betula raddeana –
- Betula saksarensis –
- Betula saviczii –
- Betula schmidtii –
- Betula sunanensis –
- Betula szechuanica – —Sichuan birch
- Betula tianshanica –
- Betula utilis – Himalayan birch
- Betula wuyiensis –
- Betula zinserlingii –
; Birches native to North America include
- Betula alleghaniensis – yellow birch
- Betula caerulea – blue birch
- Betula cordifolia – mountain paper birch
- Betula glandulosa – American dwarf birch
- Betula kenaica – Kenai birch
- Betula lenta – sweet birch, cherry birch, or black birch
- Betula michauxii – Newfoundland dwarf birch
- Betula minor – dwarf white birch
- Betula murrayana – Murray's birch
- Betula nana – dwarf birch or bog birch
- Betula neoalaskana – Alaska paper birch also known as Alaska birch or Resin birch
- Betula nigra – river birch or black birch
- Betula occidentalis – water birch or red birch
- Betula papyrifera – paper birch, canoe birch or American white birch
- Betula populifolia – gray birch
- Betula pumila – swamp birch
- Betula uber – Virginia round-leaf birch
Etymology
The generic name Betula is from Latin, which is a diminutive borrowed from Gaulish betua''.
Evolutionary history
Within Betulaceae, birches are most closely related to alder. The oldest known birch fossils are those of Betula leopoldae from the Klondike Mountain Formation in Washington State, US, which date to the early Eocene around 49 million years ago.Ecology
Birches often form even-aged stands on light, well-drained, particularly acidic soils. They are regarded as pioneer species, rapidly colonizing open ground especially in secondary successional sequences following a disturbance or fire. Birches are early tree species to become established 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 mycorrhizas, are found in some cases to be beneficial to tree growth.A large number of lepidopteran insects feed on birch foliage.
Uses
Because of the hardness of birch, it is easier to shape it with power tools; it is quite difficult to work it with hand tools.- 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 birch, from Betula verrucosa var. carelica, has ripple textures combined with attractive dark streaks and lines.
- Birch plywood is made from laminations of birch veneer. It is light but strong, and has many other good properties. It is among the strongest and dimensionally most stable plywoods, although it is unsuitable for exterior use. Birch plywood is used to make longboards, giving it a strong yet flexible ride. It is also used for making model aircraft.
- Birch wood is often used in the manufacture of popsicle sticks due to its durability, smoothness and neutral flavour.
- Extracts of birch are used for flavoring and leather oil, and in cosmetics such as soap and shampoo. In the past, commercial oil of wintergreen was made from the sweet birch.
- 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.
- Fragrant twigs of wintergreen group birches are used in saunas.
- Birch is also associated with the feast of Pentecost in Central and Eastern Europe and Siberia, where its branches are used as decoration for churches and homes on this day.
- 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 Native Americans in the United States and Indigenous peoples in Canada prize the birch for its bark, which because of its light weight, flexibility, and the ease with which it can be stripped from fallen trees, is 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 plywood was specified by the BBC as the only wood that can be used in making the cabinets of the long-lived LS3/5A loudspeaker.
- Birch is used as firewood because of its high calorific value per unit weight and unit volume. It burns well, without popping, even when frozen, or 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 wood can be used to smoke foods.
- Birch seeds are used as leaf litter in miniature terrain models.
- Birch oil is used in the manufacture of Russia leather, a water-resistant leather.