Birch

Betula spp. Family: Betulaceae

Other names
English, Finnish, Swedish etc birch, according to origin, silver birch, white birch.

Distribution
Birch is found throughout Europe, including the British Isles. It penetrates farther north than any other broad-leaved tree, being found in Lapland, and it will grow where it is subject to great heat just as well as it will endure extreme cold.

It extends from Scandinavia and northern Europe down to central Spain, and throughout the British Isles.

The tree
Two forms are recognised, Betula pendula (silver or white birch), and B. pubescens (common birch). Silver birch is the form with rough bark at its base, the branches drooping, twigs warty. leaves short-pointed and smooth, as distinct from common birch with its smooth, often reddish bark at the base, branches closer and more horizontal, and twigs and leaves softly hairy.

The trees reach a height of 18m or 20m sometimes more; in their first ten years of life they grow at a rapid rate of some 0.5m annually, putting on little girth during this period, and reaching maturity in fifty years.

The timber
There is no distinct heartwood, the wood being whitish to pale brown, without conspicuous features, fairly straight grained, fine-textured, and weighing about 670 kg/rn3 when dried.

Despite the normally featureless appearance of birch, changes in appearance occasionally take place due to beetle attack. An insect known as Agromyzia carbonaria is usually responsible, its larvae burrowing in the cambium of the tree create what are known as pith flecks, pith-like cells which cause dark markings in the wood, and localized grain disturbances. Logs that have been severely attacked, when rotary peeled, can produce highly decorative veneer known as masur birch, the irregular dark markings appearing to stand out in relief against the silky white background.

Flame birch and curly birch veneer is likewise created by grain deviations.

Drying
Birch air dries and kiln dries fairly quickly without undue difficulty beyond a tendency to warp. It should be dried quickly after conversion in order to avoid fungal discolouration, or decay.

Strength
The dried timber is similar to oak in most strength properties, and superior to that timber in compression along the grain, stiffness and toughness.

Durability
Perishable.

Working qualities
Works fairly easily but is inclined to be woolly. It can be planed and moulded to a good clean surface, and can be glued, stained and polished satisfactorily, and is a good turnery wood.

Uses
Plywood and blockboard, furniture, bobbins. dowels, fittings, turnery, veneer, and in twig form for brooms and pea sticks, and in pole form for posts after preservative treatment under pressure.