Birch

A Birch, a deciduous, thin-leaved hardwood tree, is part of the Betulaceae family, which also includes alders and hazels. 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 a typically rather short-lived pioneer species widespread in the Northern Hemisphere, particularly in northern areas of temperate climates and in boreal climates.

Description

Birch species are generally small to medium-sized trees or shrubs, mostly of northern temperate and boreal climates. Simple leaves are simple and alternate. They can be single or double serrate, feather-veined petiolate, stipulate, and singly. 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 (Alnus, another 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. Distinctive colors give the common names gray, white, black, silver and yellow birch to different species.

The buds are lateral and form early in the season. They mature by midsummer. All species have wood that is fine-grained and satiny with a good fuel value.

Flower and fruit

The flowers are monoecious, opening with or before the leaves. Once fully grown, these leaves are usually

3-6 millimetres (1/8–1/4 in) 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 mature staminate catkins have a broad ovate shape, which is round, yellow-orange below the middle, and dark chestnut brown at the apex. Each scale bears two bractlets and three sterile flowers, each flower consisting of a sessile, membranous, usually two-lobed, calyx. Each calyx contains four filaments, one-celled anthers, or strictly, two filaments that are divided into two branches each, 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. Each scale bears two to three fertile flowers. The ovary is two-celled and compressed. It is crowned with two slender styles. The ovule is single. Each scale has a single winged, small, oval nut with two persistent stigmas at its apex.

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.

As food

The inner bark can be eaten as an emergency food. You can dry it and make flour from it, just as Native Americans did. It can also be cut into strips and cooked like noodles.

The sap can be drank or used to make syrup. Tea can be made from the red inner bark of black birches.

Cultivation

White-barked birches in particular are cultivated as ornamental trees, largely for their appearance in winter. The Himalayan birch, Betula utilis, especially the variety or subspecies jacquemontii, is among the most widely planted for this purpose. Many cultivars have been used, including Doorenbos, Grayswood Ghost’, and Silver Shadow’. ‘Knightshayes’ has a slightly weeping habit. Other species with ornamental white bark include Betula ermanii, Betula papyrifera, Betula pendula and Betula raddeana.

Medical

Approved topical medicine

In the European Union, a prescription gel containing birch bark extract (commercial name Episalvan, betulae cortex dry extract (5-10 : 1); extraction solvent: n-heptane 95% (w/w)) was approved in 2016 for the topical treatment of minor skin wounds in adults. Although its mechanism of action in helping to heal injured skin is not fully understood, birch bark extract appears to stimulate the growth of keratinocytes which then fill the wound.

Research and traditional medicine

Preliminary research indicates that the phytochemicals, betulin and possibly other triterpenes, are active in Episalvan gel and wound healing properties of birch bark.

Over centuries, birch bark was used in traditional medicine practices by North American indigenous people for treating superficial wounds by applying bark directly to the skin. Splints made with birch bark were used as casts for broken limbs in the 16th century.

Paper

Wood pulp made from birch gives relatively long and slender fibres for a hardwood. Due to its thin walls, the paper will collapse upon drying. This results in a paper that is low in bulk and low in transparency. The birch fibres are, however, easily fibrillated and give about 75% of the tensile strength of softwood.^{[clarification needed]} The low opacity makes it suitable for making glassine.

The history of India is marked by the birch (Sanskrit, bhurja). This was because the thin bark that falls in winter was used extensively as writing paper. Birch paper (Sanskrit: bhurj ptr, bhurja patra) is exceptionally durable and was the material used for many ancient Indian texts. The Roman period Vindolanda tablets also use birch as a material on which to write and birch bark was used widely in ancient Russia as notepaper (beresta) and for decorative purposes and even making footwear (lapti) and baskets.^{[citation needed]}

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.^{[citation needed]} 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”.^{[citation needed]}

Birch is a common material used in drums. 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,^{[clarification needed]} 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.^{[citation needed]}

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.^{[citation needed]}

Ecology

Birches often form even-aged stands on light, well-drained, particularly acidic soils. Birches are considered pioneer species because they quickly colonize open ground, especially after 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 (ecto)mycorrhizas, are found in some cases to be beneficial to tree growth.

A large number of lepidopteran insects feed on birch foliage.

Taxonomy

Subdivision

Betula species are organised into five subgenera.

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

Etymology

The common name birch comes from Old English birce, bierce, from Proto-Germanic *berk-jon (cf. German Birke West Frisian Bjirk, an adjectival formation derived from * Berkon (cf. Dutch berk and Low German bark. Norwegian bjork. This adjectival formation is from *i>berkon/i> (cf. This root may have been derived from * Bhreh1g –, which means ‘to shine, to whiten’. It refers to the white bark of the birch. The Proto-Germanic rune berkanan is named after the birch.

The generic name betula is from Latin, which is a diminutive borrowed from Gaulish betua (cf. Old Irish bethe, Welsh bedw).