Birch species are generally small to medium-sizedtrees orshrubs, mostly of northerntemperate and borealclimates.[4] The simpleleaves are alternate, singly ordoubly serrate, feather-veined, petiolate and stipulate. They often appear in pairs, but these pairs are really borne on spur-like, two-leaved, lateralbranchlets.[5] Thefruit is a smallsamara, although the wings may be obscure in some species. They differ from thealders (Alnus, another genus in the family) in that the femalecatkins are not woody and disintegrate at maturity, falling apart to release the seeds, unlike the woody, cone-like female alder catkins.
Thebark of all birches is characteristically marked with long, horizontallenticels, and often separates into thin, papery plates, especially upon thepaper birch.[6] Distinctive colors give the common namesgray,white,black,silver andyellow birch to different species.[7]
Thebuds, forming early and full-grown bymidsummer, 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.
The flowers aremonoecious, and open with or before the leaves. Once fully grown, these leaves[clarification needed] are usually 3–6 millimetres (1⁄8–1⁄4 in) long on three-flowered clusters in the axils of the scales of drooping or erectcatkins 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.
Betula pubescens – downy birch, also known as white, European white or hairy birch (Europe, Siberia, Greenland, Newfoundland; naturalized in scattered locations in US)
Betula cordifolia – mountain paper birch (eastern Canada, Great Lakes, New England US)
Betula glandulosa – American dwarf birch (Siberia, Mongolia, Russian Far East, Alaska, Canada, Greenland, mountains of western US and New England, Adirondacks)
Betula kenaica – Kenai birch ( Alaska, northwestern North America)
Betula lenta – sweet birch, cherry birch, or black birch (Quebec, Ontario, eastern US)
Within Betulaceae, birches are most closely related to alder. The oldest known birch fossils are those ofBetula leopoldae from theKlondike Mountain Formation in Washington State, US, which date to the earlyEocene (Ypresian) around 49 million years ago.[9]
Frosty birches inKangasala, Finland in February 2013Birch trees by a river inHankasalmi, FinlandA stand of birch treesA birch tree in autumn
Birches often form even-aged stands on light, well-drained, particularlyacidic soils. They are regarded aspioneer species, rapidly colonizing open ground especially insecondary successional sequences following a disturbance or fire. Birches are early tree species to become established inprimary successions, and can become a threat to heathland if theseedlings and saplings are not suppressed by grazing or periodic burning. Birches are generally lowland species, but some species, such asBetula nana, have amontane distribution. In theBritish Isles, there is some difference between the environments ofBetula pendula andBetula 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.[10]
A large number of lepidopteran insects feed on birch foliage.
Birch plywoodFinnishbath broom calledvihta/vasta, braided from birch twigs
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.[11]
Birch wood is fine-grained and pale in colour, often with an attractivesatin-like sheen. Ripple figuring may occur, increasing the value of the timber forveneer and furniture-making. The highly decorative Masur (orKarelian) birch, fromBetula verrucosa var.carelica, has ripple textures combined with attractive dark streaks and lines.[citation needed]
Birchplywood 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 makelongboards (skateboard), giving it a strong yet flexible ride. It is also used (often in very thin grades with many laminations) for makingmodel aircraft.[citation needed]
Birch wood is often used in the manufacture ofpopsicle sticks due to its durability, smoothness and neutral flavour.[12]
Birch-tar or Russian oil extracted from birch bark isthermoplastic and waterproof; it was used as aglue on, for example,arrows, and also for medicinal purposes.[14]
Birch is also associated with the feast ofPentecost in Central and Eastern Europe and Siberia, where its branches are used as decoration for churches and homes on this day.[citation needed]
TheHughes 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-livedLS3/5A loudspeaker.[16]
Birch is used asfirewood because of its highcalorific 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.[citation needed]
Birch seeds are used asleaf litter in miniature terrain models.[17]
Birch oil is used in the manufacture ofRussia leather, a water-resistant leather.
The inner bark is considered edible as an emergency food, even when raw.[13] It can be dried and ground into flour, as was done by Native Americans and early settlers. It can also be cut into strips and cooked like noodles.[13]
Thesap can be drunk or used to makesyrup[13] andbirch beer. Tea can be made from the red inner bark of black birches.[13]
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 subspeciesjacquemontii, is among the most widely planted for this purpose. It has been cultivated since the 1870s, and manycultivars are available, including 'Doorenbos', 'Grayswood Ghost' and 'Silver Shadow'; 'Knightshayes' has a slightly weeping habit. Other species with ornamental white bark includeBetula ermanii,Betula papyrifera,Betula pendula andBetula raddeana.[18]
In the European Union, aprescriptiongel containing birch bark extract (commercial nameEpisalvan, betulae cortex dry extract (5–10 : 1); extraction solvent:n-heptane 95% (w/w)) was approved in 2016 for thetopical treatment of minor skin wounds in adults.[19] Although itsmechanism of action in helping to heal injured skin is not fully understood, birch bark extract appears to stimulate the growth ofkeratinocytes which then fill the wound.[19][20]
Preliminary research indicates that thephytochemicals,betulin and possibly othertriterpenes, are active inEpisalvan gel and wound healing properties of birch bark.[20]
Wood pulp made from birch gives relatively long and slender fibres for ahardwood. The thin walls cause the fibre to collapse upon drying, giving apaper with low bulk and low opacity. The birch fibres are, however, easily fibrillated and give about 75% of the tensile strength of softwood.[clarification needed][22] The low opacity makes it suitable for makingglassine.
InIndia, the birch (Sanskrit: भुर्ज,bhurja) holds great historical significance in the culture ofNorth India, where the thin bark coming off in winter was extensively used as writing paper. Birch paper (Sanskrit: भुर्ज पत्र,bhurja patra) is exceptionally durable and was the material used for many ancient Indian texts.[23][24] TheRoman periodVindolanda tablets also use birch as a material on which to write and birch bark was used widely in ancientRussia as notepaper (beresta) and for decorative purposes and even makingfootwear (lapti) and baskets.[citation needed]
Birch wood is sometimes used as atonewood for semiacoustic andacoustic guitar bodies, and occasionally for solid-body guitar bodies. It is also a common material used inmallets forkeyboard percussion.[citation needed] Drum manufacturers, such asGretsch andYamaha, have been known to use birch wood in the construction of drum shells, owing to its strength and colour which takes stain in an appealing way, and which can also amber over very well, while also giving the drums an appealing tone which changes depending on the type of birch used.[25]
Birch trees in spring in a park in Warsaw, Poland (1939)Birch tree forest at Ishkoman, Gilgit-Baltistan, Pakistan
Birches have spiritual importance in several religions, both modern and historical. InCeltic cultures, the birch symbolises growth, renewal, stability, initiation, and adaptability because it is highly adaptive and able to sustain harsh conditions with casual indifference. Proof of this adaptability is seen in its easy and eager ability to repopulate areas damaged by forest fires or clearings. Birches are also associated withTír na nÓg, the land of the dead and theSidhe, 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. The leaves of the silver birch tree are used in the festival of St George, held inNovosej and other villages in Albania.[26]
The birch isNew Hampshire's state tree and the national tree ofFinland and Russia. Theyellow birch is the official tree of the province ofQuebec (Canada). The birch is a very important element in Russian culture and represents the grace, strength, tenderness and natural beauty of Russian women as well as the closeness to nature of the Russians.[27] It's associated with marriage and love.[28] There are numerous folkloric Russian songs in which the birch tree occurs. TheOrnäs birch is the national tree of Sweden. TheCzech word for the month of March, Březen, is derived from the Czech word bříza meaning birch, as birch trees flower in March under local conditions. The silver birch tree is of special importance to the Swedish city ofUmeå. In 1888, theUmeå city fire 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, wide avenues were created, and these were lined with 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 calledBjörklöven, translated to English "The Birch Leaves".[citation needed]
"Swinging" birch trees was a common game for American children in the nineteenth century. American poetLucy Larcom's "Swinging on a Birch Tree" celebrates the game.[29] The poem inspiredRobert Frost, who pays homage to the act of climbing birch trees in his more famous poem, "Birches".[30] Frost once told "it was almost sacrilegious climbing a birch tree till it bent, till it gave and swooped to the ground, but that's what boys did in those days".[31]
^Forest, Félix; Savolainen, Vincent; Chase, Mark W.; Lupia, Richard; Bruneau, Anne; Crane, Peter R. (January 2005). "Teasing Apart Molecular- Versus Fossil-based Error Estimates when Dating Phylogenetic Trees: A Case Study in the Birch Family (Betulaceae)".Systematic Botany.30 (1):118–133.Bibcode:2005SysBo..30..118F.doi:10.1600/0363644053661850.
^Clark, William Arthur (January 1937)."History of fracture treatment up to the sixteenth century".The Journal of Bone & Joint Surgery.19 (1):47–63.Another method cited was that of splints made of birch bark soaked in water until quite soft. They were then carefully fitted to the limb and tied with bark thongs. On drying, they became stiff and firm. There is no record of the use of extension, but, nevertheless, very few crippled and deformed Indians were to be seen.
^Nanko, Hiroki; Button, Alan; Hillman, Dave (2005).The World of Market Pulp. US: WOMP, LLC. pp. 192–195.ISBN0-615-13013-5.
^Sanjukta Gupta, "Lakṣmī Tantra: A Pāñcarātra Text", Brill Archive, 1972,ISBN90-04-03419-6. Snippet:... the text recommends that the bark of the Himalayan birch tree (bhurja-patra) should be used for scribbling mantras ...
^Amalananda Ghosh, "An Encyclopaedia of Indian Archaeology", BRILL, 1990,ISBN90-04-09264-1. Snippet:... Bhurja-patra, the inner bark on the birch tree grown in the Himalayan region, was a very common writing material ...
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