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Birch (Betula spp.)

  • Kingdom Plantae
  • Phylum Anthophyta
  • Class Magnoliopsida
  • Order Fagales
  • Family Betulaceae
  • Genus Betula
  • Betula classification

Birch is the name of any tree of the genus Betula, in the family Betulaceae, closely related to the beech/oak family, Fagaceae. These are generally small to medium-size trees or shrubs, mostly of northern temperate climates. The simple leaves may be toothed or lobed. The fruit is a small samara, although the wings may be obscure in some species. They differ from the alders (Alnus, the 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 common name birch is derived from an old Germanic root similar to birka. The Proto-Germanic rune berkanan is named after the birch. The botanic name Betula is from the original Latin.

Comparative Analysis of Leaf Trichome Structure and Composition of Epicuticular Flavonoids in Finnish Birch Species (PDF)

birch DSCF3674

Silver Birch Betula Pendula Irish Beith

One of the most familiar trees in the British countryside, the graceful silver birch is a genuine native, having been an early coloniser at the end of the Ice Age. It is common due to easy dispersal, rapid growth and unexacting requirements. The wind-borne seeds of Betula pendula are able to colonise open ground (Gamlin, 1985) and can grow on almost any soil, but are less successful on Midland clays and on the lowland areas around the Wash. Betula woods rarely form on chalk although B. pendula is frequent on pure limestones. Rackham (1980) detected no significant present-day ecological differences between B. pendula and B. pubescens in England. It is distinguished from the related Downy Birch (B. pubescens, the other common European birch) in having hairless, warty shoots (hairy, without warts in Downy Birch), and whiter bark often with scattered black fissures (greyer, less fissured, in Downy Birch). It is also distinguished cytologically, Silver Birch being diploid (with two sets of chromosomes), whereas Downy Birch is tetraploid (four sets of chromosomes). Betula pendula is one of the most common native British trees but is also widely planted and is abundant throughout the British Isles, although not reaching the far north of Scotland or Ireland, where B. pubescens is favoured.

A pioneer species, it readily invades old fields, cleared or burnt-over land and creates conditions suitable for other woodland trees to become established. It forms an upper cliff zone above ashwoods of the Carboniferous Limestone in the northern Pennine region. It also forms a distinct pre-climax phase in the succession to oakwood on light sandy siliceous heath soils (Tansley, 1939, Rodwell 1991). British Betula are typically pioneers in two types of habitat (Atkinson 1992): forest or heathland recently cleared by felling or fire either in gaps left by canopy trees or as primary colonisers, and in habitats climatically or edaphically unsuitable for other trees, in upland zones or on peat bogs. Thus birch forest forms an altitudinal zone above and a latitudinal zone to the north of oak forest in the British Isles (Tansley, 1939). Betula species often form pioneers in the passage from heathland to forest. They are frequently associated with Quercus in oakwood on a great variety of soils (Gimingham 1984, Rodwell 1991), though not when the oaks form a close canopy, as Betula cannot tolerate deep shade and will not regenerate successfully (Kinnaird 1974). Betula pendula is also an important component of Quercus-Fraxinus excelsior woods (Gimingham 1984). The several woodland communities in which Betula is important are described by Rodwell (1991).

Silver birch trunks DSCF0855

Betula tends to improve acidic poor soils, increasing pH and nutrient status (Atkinson 1992). Since it is relatively short-lived and intolerant of shade, it is eventually out-competed by these trees. Thickets will appear on any vacant soils as long as there are no animals grazing. Betula pendula prefers drier, lighter soils (Gimingham 1984, Atkinson 1992) and some birchwoods are almost permanent in the south east Highlands and on the few remaining sandy heaths and commons in England, particularly Sussex (Wilkinson, 1976).

Birch is found throughout most of the UK and Europe and across Asia. The closely related Siberian Silver Birch (B. platyphylla) in northern Asia and Sichuan Birch (B. szechuanica) of central Asia are also treated as varieties of Silver Birch by some botanists, as B. pendula var. platyphylla and B. pendula var. szechuanica respectively. One of the reasons why birch managed to colonise the newly emerging lands following the retreat of the glaciers lies in its abundantly-produced seed, as fine as powder. Even today, it remains what botanists call a ‘pioneer’ species, one of the first trees to occupy suitable ground. That said, it is not a long-lived tree; most specimens die or succumb to fungal attack by the age of 70. However, they do offer protection to slower-growing, longer-lived tree species such as oaks, and where left to regenerate birches can play an important rôle in helping to nurture a wood.

As Betula is wind-pollinated and produces abundant, well-dispersed pollen it is very well represented in Holocene and earlier pollen records, even over-represented to the degree where correction factors need to be applied to its counts to relate them to actual tree Betula populations (Andersen 1970, Bradshaw 1981, Dickson 1984). Betula pollen has been recognised from all stages of the Quaternary (West 1980), with macrofossils of Betula pendula recovered from the Late Anglian (Oxygen Isotope Stage 8 or 10) cold stage (Godwin 1975) as well as pre-Holocene interglacials. Betula pollen and macrofossils are also well represented in sites throughout the Devensian glacial period, although often as B. nana. At Chelford, Cheshire (Simpson & West 1958), however, temporary warmer conditions about 60,000BP allowed the development of boreal woodland with tree Betula. Tree Betula pollen is a key environmental indicator of warming conditions at the end of glacial stages. During the Devensian late glacial between c.15,000 and c.10,000BP frequencies of tree Betula pollen are taken as a proxy record of climate change, their increase after c. 13,000BP signifying higher, interstadial temperatures followed by their sharp fall during the Younger Dryas (Loch Lomond Stadial) cold phase between 11,000BP and 10,000BP (Birks 1986). The sharpest reductions in Betula pollen were in Ireland at this time due to very cold sea temperatures (Watts 1980), and less marked further east. The complex climatic fluctuations of the Late Glacial produced a correspondingly complex, multi-peak Betula pollen curve at some sites in northern Britain (e.g. Bartley et al. 1976). Betula pollen is most abundant, however, in the pre-temperate and post-temperate phases of the interglacial climatic cycle. Its hardiness and rapid dispersal allows its early arrival and rapid spread before the other deciduous temperate trees arrive (Atkinson 1992). Its very rapid population expansion rates in the early Holocene have been demonstrated by Bennett (1983, 1986) and isopollen maps have been presented by Birks (1989) showing the spread of Betula woodland across almost all of the British Isles from the east from slightly before 10,000BP. Betula woodland was dominant in many parts of Britain and western Europe between 10,000BP and 9,000BP (Huntley & Birks 1983) after which it declined due to Pinus and Corylus immigration (Birks 1989). Betula bark scrolls at the Mesolithic archaeological site of Star Carr c. 9,500BP (Clark 1954) indicates that humans found uses for birch products from the earliest Holocene and the use of Betula timber for trackways and other artifacts continued

silver birch DSCF9685
throughout prehistory. As in preceding interglacials the rise of the mesocratic mixed oak forest (Birks 1986) severely reduced the available habitats for Betula although it survived in the north of Britain, as in the Western Isles, and around the tree line at high altitude. Elsewhere Betula pollen values are very low during this time and Betula had to rely on the creation of gaps within the dense deciduous forest or on very marginal environments such as drying bog surfaces. These latter were quickly colonised, and subsequent wetter conditions and peat regrowth can be recognised by a layer of birch stools just below the recurrence surface. Similar layers often occur on mineral soils beneath high altitude blanket bog, as in the north Pennines (ref) which marks the onset of paludification. Even when the Betula wood itself has not survived, resistant layers of white bark remain easily recognisable. In these wetter locations the remains are often of B. pubescens. Prior to the introduction of farming and its associated forest clearance the creation of breaks in the forest canopy would probably have been confined to the results of storms and wildfire, both of which would have removed established trees and allowed successions to begin in which Betula could flourish briefly. The use of fire in the forest by Mesolithic people may well have contributed to this (Simmons 1996) and Betula pollen frequencies rise sharply during post-fire regeneration at this time. From the start of the Neolithic period onwards human disturbance of the deciduous forest created ever more open habitats for colonisation by Betula and higher Betula values are a consistent feature of the pollen record during and after Neolithic and later forest clearance. The almost complete removal of British woodland by prehistoric and later farmers has replaced the natural changes which would have taken place in the tree flora during the last 5,000 years. Reference to earlier interglacials shows, however, that in the telocratic, later stages of an interglacial Betula is favoured again as climate and soils deteriorate and more thermophilous trees decline (West 1980, Birks 1986). The increase in Betula pollen percentages caused by human activity since c.5,000BP would very probably have occurred in the later stages of the Holocene due to natural climatic and edaphic change.

Pollen grains of Betula pendula are triangular or oval in side view, and have a well ringed and shouldered pore (Andrew, 1984). They are distinguishable from the very similar grains of B. pubescens by the latter's more hooked and sharply shouldered pores. Prentice (1981) has separated Betula pollen grains using size frequency data. Tree birch pollen grains are more easily distinguishable from dwarf birch (B. nana) grains (Birks 1968).

View Uppsala University images of Betula pendula by clicking here

A medium sized, fast growing, light demanding and short lived decidious tree up to 25 metres in height, exceptionally up to 30 m. Rapid growth for first 20 years, growing to 20m by 10m at a fast rate and mature at 40 years. Max age 60 - 80 years. Seldom planted in the UK by foresters although major timber species in Scandinavia, but important for conservation use in woodland.

When the tree is young the bark is a reddish-brown colour, but as the tree matures it becomes silver-white. Its papery-white bark – almost pink in young trees – distinguishes it from the downy birch Betula pubescens which has reddish bark that turns grey with age and is usually found in wetter habitats in the uplands. As silver birch ages, its bark darkens and becomes rougher and more fissured and prone to attack by the birch polypore fungus Piptoporus betulinus.

birch bark DSCF3654 Birch bark DSCF0852 birch bark DSCF3647

The catkins appear early in spring and release their pollen in clouds during April, and the seeds ripen from July to August. The scented flowers are monoecious (individual flowers are either male or female, but both sexes can be found on the same plant) and are pollinated by Wind the small (1-2 mm) winged seeds ripening in late summer on 3-5 cm long catkins.

Silver birch catkin DSCF4937 silver birch catkin and flower DSCF4942
birch leaf - betula pendula DSCF6328

The shoots are rough with small warts, and hairless, and the small leaves 3-6 cm long, triangular or diamond in shape with a broad base and pointed tip, and coarsely serrated margins. The leaves emerge shortly after the catkins, a bright emerald green at first and finally turning golden in autumn. The leaves of silver birch are and roughly . They are toothed on both sides and borne on slender warty twigs that shiver in the slightest breeze.

Saplings also share this tendency to sway in the wind and, traditionally, foresters would remove young birches from plantations to avoid them flaying more valuable trees.

Propagation and growth: Normally grown from seed although can be grown from cuttings. The seeds are brown flakes with yellow seed are wind dispersed sprouting the following spring in rock crevices or clear damp earth. Approx 150,000 seeds per Kg. Useful as a nurse species and soil improver. A good plant to grow near the compost heap, aiding the fermentation process. It is also a good companion plant, its root action working to improve the soil.

Cultivation details A very easily grown plant, it tolerates most soils including poor ones, sandy soils and heavy clays. It prefers a well-drained loamy soil in a sunny position. It is occasionally found on calcareous soils in the wild but it generally prefers a pH below 6.5, doing well on acid soils. Fairly wind tolerant though it becomes wind shaped when exposed to strong winds.

Propagation Seed - best sown as soon as it is ripe in a light position in a cold frame. Only just cover the seed and place the pot in a sunny position. Spring sown seed should be surface sown in a sunny position in a cold frame. If the germination is poor, raising the temperature by covering the seed with glass can help. When they are large enough to handle, prick the seedlings out into individual pots and grow them on in a cold frame for at least their first winter. Plant them out into their permanent positions in late spring or early summer, after the last expected frosts. If you have sufficient seed, it can be sown in an outdoor seedbed, either as soon as it is ripe or in the early spring - do not cover the spring sown seed. Grow the plants on in the seedbed for 2 years before planting them out into their permanent positions in the winter.

Other Uses Adhesive; Besom; Charcoal; Compost; Dye; Essential; Fibre; Fungicide; Hair; Paper; Pioneer; Polish; Repellent; Tannin; Thatching; Waterproofing; Wood.

The bark is used to make drinking vessels, canoe skins, roofing tiles etc. It is waterproof, durable, tough and resinous. Only the outer bark is removed, this does not kill the tree. It is most easily removed in late spring to early summer. A glue is made from the sap.

The wood is white to pale fawn in colour and easily worked. Flexible and tough but not very strong. Trees in Britain commonly rotten in centre reducing usefulness. Uses of wood - Good firewood and pulpwood. Treated wood used for fence posts. Used in turnery and formerly for cotton reels and bobbins. Larger timber not usually produced in Britain. Birch wood has little strength as a timber although in the past it was used extensively in the Highlands of Scotland. The Highlanders made almost anything from it, including their furniture and houses. Traditionally, the suppleness of the branches and twigs was exploited for making besoms or ‘witches’ brooms. Smaller versions of this implement, stripped of bark, are still popular as kitchen whisks. Besoms were also used as fire beaters but, today, the Forestry Commission uses a less flammable material. Hardly surprising when you consider that birch bark and twigs are one of the best materials for starting a fire! It is used for a wide range of purposes including furniture, tool handles, toys and carving. A high quality charcoal is obtained from the bark. It is used by artists, painters etc. The wood is also pulped and used for making paper.

The leaves are a good addition to the compost heap, improving fermentation. The young branches are very flexible and are used to make whisks, besoms etc. They are also used in thatching and to make wattles.

Moxa is made from the yellow fungous excrescences of the wood, which sometimes swell out of the fissures.

Edible Uses Flowers; Inner bark; Leaves; Sap.

Inner bark - cooked or dried and ground into a meal. It can be added as a thickener to soups etc or can be mixed with flour for making bread, biscuits etc. Inner bark is generally only seen as a famine food, used when other forms of starch are not available or are in short supply.

Young leaves - raw or cooked. A tea is made from the leaves and another tea is made from the essential oil in the inner bark.

Sap - raw or cooked. A sweet flavour. Birches produce an abundance of sap in spring and a cut stump will continue to ‘bleed’ for weeks. It is harvested in early spring, before the leaves unfurl, by tapping the trunk. It makes a pleasant drink. It is often concentrated into a syrup by boiling off the water. Between 4 and 7 litres can be drawn off a mature tree in a day and this will not kill the tree so long as the tap hole is filled up afterwards. However, prolonged or heavy tapping will kill the tree. The flow is best on sunny days following a frost. In the UK,a technique is employed by makers of birch tree wine, a drink once believed to have medicinal properties, including those of curing kidney stones and skin complaints. The sap can be fermented into a beer. An old English recipe for the beer is as follows:- "To every Gallon of Birch-water put a quart of Honey, well stirr'd together; then boil it almost an hour with a few Cloves, and a little Limon-peel, keeping it well scumm'd. When it is sufficiently boil'd, and become cold, add to it three or four Spoonfuls of good Ale to make it work...and when the Test begins to settle, bottle it up . . . it is gentle, and very harmless in operation within the body, and exceedingly sharpens the Appetite, being drunk ante pastum.".

Medicinal Uses Anticholesterolemic; Antiinflammatory; Antirheumatic; Antiseptic; Astringent; Bitter; Cholagogue; Diaphoretic; Diuretic; Laxative; Lithontripic; Miscellany; Skin.

The bark is diuretic and laxative. The inner bark is bitter and astringent, it is used in treating intermittent fevers. An oil obtained from the inner bark is astringent and is used in the treatment of various skin afflictions, especially eczema and psoriasis. The bark is usually obtained from trees that have been felled for timber and can be distilled at any time of the year. A tar-oil is obtained from the white bark in spring. It has fungicidal properties and is also used as an insect repellent. It makes a good shoe polish. Another report says that an essential oil is obtained from the bark and this, called 'Russian Leather' has been used as a perfume. A decoction of the inner bark is used to preserve cordage, it contains up to 16% tannin. A brown dye is obtained from the inner bark. Cordage can be made from the fibres of the inner bark. This inner bark can also be separated into thin layers and used as a substitute for oiled paper. An oil similar to Wintergreen oil (obtained from Gaultheria procumbens) is obtained from the inner bark. It is used medicinally and also makes a refreshing tea. The vernal sap is diuretic.

The leaves are anticholesterolemic and diuretic. They also contain phytosides, which are effective germicides. An infusion of the leaves is used in the treatment of gout, dropsy and rheumatism, and is recommended as a reliable solvent of kidney stones. The young shoots and leaves secrete a resinous substance which has acid properties, when combined with alkalis it is a tonic laxative. The young leaves and leaf buds are harvested in the spring and dried for later use. The buds are balsamic. The young leaves are a diuretic. A decoction of the leaves and bark is used for bathing skin eruptions.

Feeding and other inter-species relationships Associated with Betula pendula:

Due to its invasive nature, silver birch scrub is often the reason why conservation work is carried out on some nature reserve sites. Birch colonises open areas quickly and, when left unchecked, can reduce the conservation value of habitats such as heathland. In consequence, there are no specific projects for conserving the species.

Although closely related, it does not usually hybridize with B. pubescens. although some research believes that there may be some form of hybridization.
Extensive sharing of chloroplast haplotypes among European birches ... (PDF)

Ozone: Ozone induces initial macroscopic leaf symptoms which appear as isolated light-green dots on the upper leaf side in intercostal fields. After a fine weather period lasting more than 14 days with an ozone concentration of 60 nll-1, or a total ozone dose (concentration x time) from flushing of 25-50 mll-1h, or an AOT40 (daylight hours) around 8 mll-1h, the dots are spread visibly over the whole leaf lamina depending on the climate, site and genetic properties which determine ozone uptake. The initial dots develop into bronze-green or necrotic dots (stippling), which sometimes are more visible on the darker shade leaves or in shaded trees. In contrast, symptom development is less advanced on leaf parts which lie in the shadow of other leaves. At a 10-fold magnification, the light-green dots are diffuse and stippling appears grey, indicating groups of collapsed cells. Symptoms increase with ozone dose (leaf age). The injury symptoms lead to autumnal leaves with a heterogeneous discoloration together with green parts and necrotic spots and premature leaf shedding. In contrast, autumnal leaves unaffected by ozone, display a more homogeneous discoloration from green to yellow.

Leaf symptoms of other origin, which may be mistaken for those of ozone: In contrast to diffuse ozone symptoms, spot and point symptoms of biotic origin are rather discrete. Light points originate from empty mesophyll cells and show traces of sucking insects. Whereas leaf symptoms from spidermite infections (yellowish points) are accompanied by webs, larvae or eggs, which can be detected with a hand lens; leafhoppers fly off and larvae detach at the slightest vibration. White points are a sign of their presence. Limited discrete necrotic spots from fungus infections can be discriminated from ozone symptoms by their fruit bodies using a hand lens.

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Downy Birch Betula pubescens

Downy Birch (Betula pubescens) is a species of birch, native and abundant throughout northern Europe, Iceland, northern Asia and also Greenland. It is found throughout the UK. It is also known as White Birch, European White Birch or Hairy Birch. It is a deciduous tree growing to 10-20 m tall (rarely to 27 m), with a slender crown and a trunk up to 70 cm (exceptionally 1 m) diameter, with smooth but dull grey-white bark finely marked with dark horizontal lenticels.

It is closely related to, and often confused with, the Silver Birch (B. pendula). 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 name B. pendula of the other species), but they are regarded as distinct species throughout Europe. Downy Birch can be distinguished from Silver Birch in having smooth, downy shoots, which are hairless and warty in Silver Birch. The bark of the Downy Birch is a dull greyish white, whereas the Silver Birch has striking white papery bark with black fissures. The leaf margins also differ, finely serrated in Downy Birch, coarsely double-toothed in Silver Birch. They are also distinguished cytologically, Silver Birch being diploid (with two sets of chromosomes), whereas Downy Birch is tetraploid (four sets of chromosomes). The two have differences in habitat requirements, with Downy Birch more common on wet, poorly drained sites such as clays and peat bogs, and Silver Birch found mainly on dry, sandy soils.

Downy Birch extends farther north into the Arctic than any other broadleaf tree. These subarctic populations are usually small and very contorted, and are often distinguished as Arctic Downy Birch, Betula pubescens subsp. tortuosa. This subspecies is notable as being the only tree native to Greenland, where large specimens can reach 5-6 m tall.

Much more common than the silver birch (Betula pendula) in Ireland. The leaf lacks the long point of the silver birch and the bark is darker, often remaining brownish even when mature, and generally less attractive.

The downy birch gets its name from the hairs found on the shoots and leaf stalks. The shoots are grey-brown and finely downy. The leaves of the downy birch have toothed edges. The leaves are ovate-acute, 2-5 cm long and 1.5-4.5 cm broad, with a finely serrated margin.

In winter the tree produces grey coloured catkins. In April and May they turn a yellow colour as they open up to shed their pollen before the leaves. They are often referred to as "lambs tails". The scented flowers are monoecious (individual flowers are either male or female, but both sexes can be found on the same plant) and are pollinated by Wind. The wind carries the pollen to the short green female catkins. The fertilised catkins remain on the tree until winter when they break up into winged seeds. The fruit is a pendulous cylindrical aggregate 1-4 cm long and 5-7 mm diameter, which disintegrates at maturity releasing the individual seeds; these are 2 mm long with two small wings along the side.

Extensive sharing of chloroplast haplotypes among European birches ... (PDF)

Medicinal Uses Antirheumatic; Astringent; Bitter; Diaphoretic; Diuretic; Lithontripic; Miscellany; Skin.
Anti-inflammatory, cholagogue, diaphoretic.
The bark is diuretic and laxative.
The inner bark is bitter and astringent, it is used in treating intermittent fevers.
An oil obtained from the inner bark is astringent and is used in the treatment of various skin afflictions, especially eczema and psoriasis. The bark is usually obtained from trees that have been felled for timber and can be distilled at any time of the year.
The buds are balsamic. The young shoots and leaves secrete a resinous substance which has acid properties, when combined with alkalis it is a tonic laxative.
The leaves are anticholesterolemic and diuretic. They also contain phytosides, which are effective germicides. An infusion of the leaves is used in the treatment of gout, dropsy and rheumatism, and is recommended as a reliable solvent of kidney stones. The young leaves and leaf buds are harvested in the spring and dried for later use.
A decoction of the leaves and bark is used for bathing skin eruptions.
The vernal sap is diuretic.
The boiled and powdered wood has been applied to chafed skin.
Moxa is made from the yellow fungous excrescences of the wood, which sometimes swell out of the fissures.

Feeding and other inter-species relationships Associated with Betula pubescens:

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Alder Betula

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