Betula pendula, commonly known assilver birch,warty birch,European white birch,[2] orEast Asian white birch,[3] is aspecies of tree in thefamilyBetulaceae,native to Europe and parts of Asia, though in southern Europe, it is only found at higher altitudes. Its range extends into Siberia, China, and southwest Asia in the mountains of northern Turkey, the Caucasus, and northern Iran. It has been introduced into North America, where it is known as theEuropean white birch orweeping birch[4] and is consideredinvasive in some states in the United States and parts of Canada.
The silver birch is a medium-sizeddeciduous tree that owes its common name to the white peeling bark on the trunk. The twigs are slender and often pendulous and the leaves are roughly triangular withdoubly serrate margins and turn yellow and brown in autumn before they fall. The flowers arecatkins and the light, winged seeds get widely scattered by the wind. The silver birch is a hardy tree, apioneer species, and one of the first trees to appear on bare or fire-swept land. Many species of birds and animals are found in birch woodland, the tree supports a wide range of insects and the light shade it casts allows shrubby and other plants to grow beneath itscanopy. It is planted decoratively in parks and gardens and is used for forest products such as joinery timber, firewood, tanning, racecourse jumps, and brooms. Various parts of the tree are used intraditional medicine and the bark containstriterpenes, which have been shown to have medicinal properties.
Silver birchSilver birch has often pendulous twigs, after which the tree has received its scientific name.
The silver birch typically reaches 15 to 25 m (49 to 82 ft) tall, exceptionally up to 31 m (102 ft),[5] with a slender trunk usually under 40 cm (1 ft 4 in) diameter. The bark on the trunk and branches is golden-brown at first, but later this turns to white as a result of papery tissue developing on the surface and peeling off in flakes, in a similar manner to the closely relatedpaper birch (B. papyrifera). The bark remains smooth until the tree gets quite large, but in older trees, the bark thickens, becoming irregular, dark, and rugged. Young branches have whitishresin warts and the twigs are slender, hairless, and oftenpendulous. The buds are small and sticky, and development issympodial – the terminal bud dies away and growth continues from a lateral bud. The species ismonoecious with male and female catkins found on the same tree.[6] Someshoots are long and bear the malecatkins at the tip, while others are short and bear female catkins. The immature male catkins are present during the winter, but the female catkins develop in the spring, soon after the leaves unfurl.[5]
Theleaves have short, slender stalks and are 3 to 7 cm (1+1⁄8 to2+3⁄4 in) long, triangular with broad, untoothed, wedge-shaped bases, slender pointed tips, and coarsely double-toothed, serrated margins. They are sticky with resin at first, but this dries as they age, leaving small, white scales. The foliage is a pale to medium green and turns yellow early in the autumn before the leaves fall. In midsummer, the female catkins mature and the male catkins expand and release pollen, and wind pollination takes place. A catkin of Silver birch could produce an average of 1.66 million pollen grains.[7] The small, 1- to 2-mm wingedseeds ripen in late summer on pendulous, cylindrical catkins2 to 4 cm (3⁄4 to1+5⁄8 in) long and7 mm (1⁄4 in) broad. The seeds are very numerous and are separated by scales, and when ripe, the whole catkin disintegrates and the seeds are spread widely by the wind.[5][8]
Silver birch can easily be confused with the similardowny birch (Betula pubescens). Yet, downy birches are characterised by hairy leaves and young shoots, whereas the same parts on silver birch are hairless. The leaf base of silver birch is usually a right angle to the stalk, while for downy birches, it is rounded. In terms ofgenetic structure, the trees are quite different, but do, however, occasionallyhybridize.[6]
The silver birch grows naturally from western Europe eastwards toKazakhstan, theSakha Republic inSiberia, Mongolia, and theXinjiang province in China, and southwards to the mountains of the Caucasus and northern Iran, Iraq, and Turkey. It is also native to northern Morocco and has become naturalised in some other parts of the world.[9] In the southern parts of its range, it is mainly found in mountainous regions. Its light seeds are easily blown by the wind and it is a pioneer species, one of the first trees to sprout on bare land or after a forest fire. It needs plenty of light and does best on dry, acid soils and is found on heathland, mountainsides, and clinging to crags.[5] Its tolerance to pollution make it suitable for planting in industrial areas and exposed sites.[10] It has been introduced into North America, where it is known as the European white birch, and is consideredinvasive in the states ofKentucky,Maryland,Washington, andWisconsin.[11] It isnaturalised and locally invasive in parts ofCanada.[12]
Betula pendula subsp.pendula – Europe and eastwards to central Asia
Betula pendula subsp.mandshurica(Regel) Ashburner & McAll. – eastern Asia and western North America; treated by some botanists asBetula platyphylla[14]
B. pendula is distinguished from the relatedB. pubescens, the other common European birch, in having hairless, warty shoots (hairy and without warts in downy birch), more triangular leaves with double serration on the margins (more ovoid and with single serrations in downy birch), and whiter bark often with scattered black fissures (greyer, less fissured, in downy birch). It is also distinguishedcytologically, silver birch beingdiploid (with two sets of chromosomes), whereas downy birch istetraploid (four sets of chromosomes). Hybrids between the two are known, but are very rare, and being triploid, are sterile.[15] The two have differences inhabitat requirements, with silver birch found mainly on dry,sandy soils, and downy birch more common on wet, poorly drained sites such asclay soils andpeat bogs. Silver birch also demands slightly more summer warmth than does downy birch, which is significant in the cooler parts of Europe. Many North American texts treat the two species as conspecific (and cause confusion by combining the downy birch's alternative vernacular name 'white birch', with the scientific nameB. pendula of the other species), but they are regarded as distinct species throughout Europe.[8]
Severalvarieties ofB. pendula are no longer accepted, includingB. pendula var.carelica,fontqueri,laciniata,lapponica,meridionalis,microlepis, andparvibracteata, as well asformsBetula pendula f.bircalensis,crispa, andpalmeri.[13] Other synonyms include:[13][16]
The rejected nameBetula albaL. also applied in part toB. pendula, though also toB. pubescens[17]
Betula brachylepisV.N.Vassil.
Betula cajanderi f. fruticansKozhevn.
Betula carpatica var. sudeticaRchb.
Betula coriaceaPamp.
Betula cycoviensisSteud.
Betula ellipticifoliaV.N.Vassil.
Betula etnensisRaf., sometimes spelledB. aetnensis[1]
Betula ferganensisV.N.Vassil.
Betula fontqueriRothm.
Betula gummiferaBertol.
Betula hybridaBlom
Betula insularisV.N.Vassil.
Betula kossogolicaV.N.Vassil.
Betula laciniata(Wahlenb.) Rchb.
Betula lobulataKit.
Betula ludmilaeV.N.Vassil.
Betula microlepisI.V.Vassil.
Betula mongolicaV.N.Vassil.
Betula montanaV.N.Vassil.
Betula oycowiensisBesser, sometimes spelledB. oycoviensis[1]
The silver birch has an open canopy which allows plenty of light to reach the ground. This allows a variety of mosses, grasses, and flowering plants to grow beneath, which in turn attract insects. Flowering plants often found in birch woods includeprimrose (Primula vulgaris),violet (Viola riviniana),bluebell (Hyacinthoides non-scripta),wood anemone (Anemone nemorosa), andwood sorrel (Oxalis acetosella). Small shrubs that grow on the forest floor includeblaeberry (Vaccinium myrtillus) andcowberry (Vaccinium vitis-idaea).[8]Birds found in birch woodland include thechaffinch,tree pipit,willow warbler,nightingale,robin,woodcock,redpoll, andgreen woodpecker.[10]
The branches of the silver birch often have tangled masses of twigs known aswitch's brooms growing among them, caused by the fungusTaphrina betulina. Old trees are often killed by the decay fungusFomitopsis betulina and fallen branches rot rapidly on the forest floor. This tree commonly grows with themycorrhizal fungusAmanita muscaria in amutualistic relationship. This applies particularly to acidic or nutrient-poor soils. Other mycorrhizal associates includeLeccinum scabrum andCantharellus cibarius.[8] In addition to mycorrhiza, the presence of microfauna in the soil assists the growth of the tree, as it enhances the mobilization of nutrients.[18]
The larvae of a large number of species of butterflies, moths, and other insects feed on the leaves and other parts of the silver birch.[19] In Germany, almost 500 species of insects have been found on silver and downy birch including 106 beetles and 105lepidopterans, with 133 insect species feeding almost exclusively on birch.[20]Birch dieback disease can affect planted trees, while naturally regenerated trees seem less susceptible.[21] This disease also affectsB. pubescens and in 2000 was reported at many of the sites planted with birch in Scotland during the 1990s.[22] In the United States, the wood is attacked by the bronze birch borer (Agrilus anxius), an insect pest to which it has no natural resistance.[11]
Betula pendula is considered a species of least concern by theIUCN Red List.[1] The synonymBetula oycowiensis (asB. oycoviensis) was previously listed on the Red List as vulnerable,[23] though it is now considered a synonym ofB. pendula subsp.pendula.[1][13]B. szaferi was previously considered extinct in the wild on the Red List, but is now considered a form ofB. pendula with the presence of a mutant gene, causing it to grow weakly and fruit heavily.[1]
The silver birch is Finland'snational tree.[24] Leafy, fragrant bunches of young silver birch boughs (calledvihta orvasta) are used to gently beat oneself while bathing in the Finnishsauna.[25] Silver birch is often planted in parks and gardens, grown for its white bark and gracefully drooping shoots, sometimes even in warmer-than-optimum places such asLos Angeles andSydney. In Scandinavia and other regions of northern Europe, it is grown for forest products such as lumber and pulp, as well as for aesthetic purposes andecosystem services. It is sometimes used as apioneer and nurse tree elsewhere.[5]
Silver birch wood is pale in colour with a light reddish-brown heartwood and is used in making furniture, plywood, veneers, parquet blocks, skis, and kitchen utensils, and inturnery. It makes a good firewood, but is quickly consumed by the flames. Slabs of bark are used for makingroof shingles and strips are used for handicrafts such asbast shoes and small containers.[5] Historically, the bark was used fortanning. Bark can be heated and the resin collected; the resin is an excellent waterproof glue and useful for starting fires. The thin sheets of bark that peel off young wood contain a waxy resin and are easy to ignite even when wet. The dead twigs are also useful as kindling for outdoor fires.[26] The removal of bark was at one time so widespread thatCarl Linnaeus expressed his concern for the survival of the woodlands.[27]
Birch brushwood is used forracecourse jumps andbesom brooms. In the spring, large quantities of sap rise up the trunk and this can be tapped. It contains around 1% sugars and can be used in a similar way tomaple syrup, being drunk fresh, concentrated by evaporation, or fermented into a "wine".[26]
The outer part of thebark contains up to 20%betulin. The main components in the essential oil of thebuds areα-copaene (~10%),germacrene D (~15%), andδ-cadinene (~13%).[28] Also present in the bark are othertriterpene substances which have been used in laboratory research to identify its possible biological properties.[29]
Successful birch cultivation requires a climate cool enough for at least the occasional winter snowfall. As they are shallow-rooted, they may require water during dry periods. They grow best in full sun planted in deep, well-drained soil.[33]
'Carelica' or "curly birch" is calledvisakoivu in Finland. The wood is hard andburled throughout; it is prized for its decorative appearance and is used in wood-carving and as veneer.[34]
'Laciniata'agm[35] (commonly misidentified as'Dalecarlica') has deeply incised leaves and weeping branches
^abVakkari P (2009)."Silver birch (Betula pendula)"(PDF).EUFORGEN Technical Guidelines for Genetic Conservation and Use. Archived fromthe original(PDF) on 18 January 2017. Retrieved17 January 2017.
^"Filsuvez EPAR".European Medicines Agency (EMA). 13 April 2022.Archived from the original on 6 July 2022. Retrieved6 July 2022. Text was copied from this source which is copyright European Medicines Agency. Reproduction is authorized provided the source is acknowledged.
^Botanica's Trees & Shrubs. San Diego, Calif.: Laurel Glen Publishing. 1999. p. 139.ISBN978-1-57145-649-6.
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