Birches

Silver birch
Betula pendula

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Silver birch belongs to the genus Betula and is a member of the birch family (Betulaceae).

Silver birch (Betula pendula) is a deciduous tree growing up to 30m and flowering April to May.

Lifespan: Rarely lives beyond 100 years.

 

Characteristics

Bark is white and papery when young; flaking to reveal dark fissures with age. Twigs are hairless and warted with resin glands. Branches have a drooping ‘pendulus’ appearance.

Leaves are alternate, pointed, triangular, hairless and doubly-toothed.

Silver birch is monoecious: both male and female flowers are found on the same tree. Both flowers are arranged as a catkin (‘little cat’), as they resemble a kitten’s tail.

Male flowers are long, yellow-brown catkins which hang in groups of two to four at the tips of shoots. Female catkins are smaller, short, green and erect. After wind pollination they become brown and thicken. Seeds are tiny winged nutlets produced in large numbers and wind dispersed.

Silver birch tree
Silver birch leaves

Distribution

Native throughout Europe and in the UK where it is often found in dry woodlands, downs and heaths of the south and east at low altitudes. The species is able to tolerate a wide range of temperatures and grows as far south as Spain and as far north as Lapland.

Silver birch has been widely planted as an ornamental or garden tree. It frequently hybridises with our other native birch, the downy birch (Betula pubescens), and their ranges also overlap.

Both species are very similar, have similar human uses and wildlife value. They are often cited in woodland terms as though they were one species. For example, birch woodland (which may be made up of silver and/or downy birch) accounts for 16% of broadleaf woodland in the UK and birch is one of the most common broadleaf trees in the UK in either form; second only to oak.

Human value

Silver birch timber is whitish to pale brown with no distinct heartwood. It is straight-grained with a fine texture. It has similar strength properties to oak but is not as durable. The timber works fairly easily and is good for turnery.

Silver birch wood is of little commercial value in Britain because the trees do not reach large sizes. In other parts of Europe the trees grow much larger.

Modern uses include furniture, veneers, plywood and pulp; the wood also makes good firewood and the twigs are still used to make hurdles and sweeping brooms or ‘besoms’.

Silver birch can be planted to improve soil quality; the roots grow very deep underground and draw up nutrients into the leaves and branches. When the leaves fall, any unused nutrients are made available to the rest of the forest through recycling. Birch is also valuable as a nursing tree to protect oak, beech or frost-tender conifers.

This species may be increasingly vulnerable to drought with climate change.

Silver birch is a slender, graceful tree; nicknamed ‘the lady of the woods’.

Silver birch flowers
Silver birch flowers (photo)

Wildlife value

Silver birch is a very important wildlife tree and is valued as a resource for conservation, habitat and landscape purposes.

Upland birch woods are a priority habitat under the UK Biodiversity Action Plan. Birch woods (which may be made up of silver and/or downy birch) have a light, open canopy and a characteristic plant community of grasses, wood anemone, bluebells, wood sorrel and violets.

Silver birch leaves attract aphids which in turn provide food for many ladybird species and blue, great and long-tailed tits. The leaves are also food for the angle-shades moth, the buff tip, the pebble hook-tip, and the large and little emerald moths. Threatened moths which like birches include the argent and sable, the cousin German, the Kentish glory and silvery arches.

Silver birch supports well over 300 insect species; a fact that makes these trees a favoured foraging place for woodpeckers which often make nesting holes in the trunk. Birch seeds also provide winter food for siskins, greenfinches and redpolls.

Birch woodland is rich in fungi; the tree forms symbiotic associations with specific species such as the fly agaric, woolley milk cap, birch milk cap, birch brittlegill, birch knight, chanterelle and the birch polypore (razor strop).

Management

Silver birch is a light-loving pioneer species which readily colonises open ground and grows fast when young. A very hardy tree, it is frost resistant and wind firm, able to grow at high elevations on a wide range of soils, from lighter acid soils, gravels and shallow peats to clay and tolerates poor to medium soil fertility. It is less common on calcareous soils. The absence of birch from a site is said to indicate a deficiency of phosphate in the soil.

Seeds ripen July to August and naturally disperse straight away, so need to be collected during this time. Seeds require pre-treatment to simulate cold conditions before planting March to April.

Silver birch is susceptible to a rust pathogen Melamsporidium betulinum which can affect growth and health. Dieback can occur in association with two canker fungi – Discula betulina and Marssonina betulae – and birch can also be affected by the honey fungus, Armillaria.

The parasitic witches’ broom fungus (Taphrina betulina) can cause abnormally dense growths of small twigs on branches.

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Birch wood

Downy birch
Betula pubescens

Downy birch tree trunk

Downy birch (Betula pubescens) is also a member of the Betula genus. It is a deciduous tree growing up to 30m and flowering April to May.

Downy birch has only subtly different characteristics from silver birch and the two species frequently hybridise. Their human use, timber type and wildlife value is almost identical.

The bark of the downy birch is more brown in colour, peeling and papery with more conspicuous horizontal grooves. Twigs are downy but not warted. Leaves are oval-triangular, more rounded at the base, simply toothed and downy on the underside. It is more upright in growth than silver birch.

Downy birch is the UK’s other native birch; more frequently found on badly drained sites or damper soils than silver birch. It can tolerate waterlogged or peaty conditions in the north and west at higher elevations.

Seeds ripen in August to September and naturally disperse straight away, so need to be collected during this time. Seeds require pre-treatment to simulate cold conditions before planting March to April.

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Illustrations © Reader’s Digest Association, Inc.
Photographs © Forestry Commission
Downy birch © Debbie Cotton