fine young figure is clothed in smooth white satin.
In spring she dons upon her head a veil of pale green,
shimmering in the warm breeze.
Her luring perfume is as fresh as the April rains.
In autumn her veil is the golden-yellow of the Sun.
As the Sun fades so her veil falls gently to the ground
and she scatters new life upon the air.
silver birch (Betula
pendula) is also known as the
Lady of the Woods with her slender silver-white frame, small
delicate leaves and seeds and subtle but enchanting fragrance.
The birch is a pioneer species across much of Britain - it is a
smallish, relatively short-lived tree that reproduces and grows
quickly, exploiting openings in the tree canopy before other
slower growing trees like oak eventually take over. In Scotland,
however, birch is a dominant species along with pine with which
it forms mixed woodland, due to its ability to endure cold and
thrive on poor acid highland soils. Indeed parts of the
Caledonian forest are essentially original wildwood, apart from
the odd grazing by deer and sheep, they are little changed from
their wild state since they took root after the Ice Age.
Question: what is a pioneer species? A pioneer species is one of the first species to colonise newly exposed ground, be it a gap in a forest canopy where a tree has fallen (colonised by birch), or newly solidified volcanic rock (colonised by bacteria and lichens) or exposed desert rocks (colonised by bacteria), etc. To beat their rivals pioneer species must have a way to arrive on the scene quickly. The birch tree does this by producing millions of very tiny seeds with wings that carry them far and wide on the air. Wherever a gap appears, if the soil is suitable, then a birch seed is almost bound to find the area and take root. Pioneers must also be fast-growing to beat competitors - in the case of trees they must reach the light before rivals drown them out. Birch achieves this by investing in a tall but slender trunk, but at the expense of longevity. Longer lived trees invest more in a thicker trunk, which means that they areslower growing and not effective pioneer species.
Some drawings of parts of silver birch trees that I made: a small branch, showing lenticels, a strip of bark, showing lenticels, a leaf, showing some of the veination, a close up of part of the leaf showing its vasculature and a birch 'seed' (actually a fruit) with its two wings.Question: what is a lenticel? A lenticel is an opening, usually a small slit, in the bark of a tree that allows oxygen in
There are about 40 species of birch. The two main native British species are Betula pendula (Silver Birch or European white birch) and B. pubescens (Downy Birch or White birch).
Height – 28 m, Max. 38 m
(silver birch: 25 m, downy birch: 28 m).
Longevity - 80 years, rarely > 100, occasionally up to 200 years. Birch is a pioneer of open areas and invests in a tall thin trunk of less durable wood that grows in height quickly, but is therefore more prone to windfall.
Habitat - Birch is a fast-growing pioneer on acid soils, rarely growing on chalk and is found on nutrient-poor sands and peat. Silver birch prefers dry sandy/gravelly soils -heathlands of southern England. Downy birch prefers wetter soils and a cooler climate- uplands of Scotland, Wales and Ireland. Birches are tolerant to frost, but susceptible to sulphur dioxide damage.
Bark - thin, paper-like shed
in strips as the tree grows. Remarkably resistant to decay and
water proof (has been used for roofing). Phellem with thick cell
walls and conspicuous growth layers (B.
Type 3 lenticels, visible as horizontal Slits, up to about 5 cm
long. Bark of B.
peels in horizontal strips. Alternating layers of thin- and
thick-walled cork cells results in the shedding of thin papery
sheets of bark.
Phellem is the corky tissue produced in the bark of trees and is
both waterproof and protects the vital sugary sap-conducting cells
(phloem) beneath the outer layers of bark against knocks and blows
and would-be grazers and insects which have a hard job getting
through the corky tissue to the critical phloem underneath. Bark
also gives the tree a degree of fire-resistance.
Wood - burns well -still the
main winter fuel in parts of Scandinavia and central Europe.
Timber is a pale cream-brown colour - a hard but perishable wood.
Birches have diffuse porous wood. The sugary spring sap, flowing
through the trunk, is tapped to make wine.
Leaves - appear towards end of
April, unfolding from small, pointed buds arranged alternately
along the thin, purplish-brown twigs. Bright green, 3 cm long,
usually triangular, but varying from diamond to oval. Unevenly
toothed margins, taper to a point. Borne on slender stalks,
allowing them to twist and flutter in the breeze. Often much
larger leaves on young trees. Turn bright yellow in autumn,
falling in October. Glandular
and colleters on young leaf primordia (young leaf buds)
produce a sticky resin that covers and permeates the entire bud.
After a heavy shower, in spring, the aromatic resin washed from
the unfurling leaves, and from tiny warts on the twigs, leaves a
noticeable fragrance in the air. On average, a birch tree has some
200 000 leaves and a normal sized birch tree uses some 17 000
litres of water in summer.
Flowers – monoecious (single
sex) catkins of both sexes are borne on the same tree. Males
develop during autumn and are about 5cm long by April/May and
covered by reddish brown scales, which separate to release their
pollen. Female catkins develop while the leaves unfold, and are
about 2-3 cm long and held upright on the twigs and are made up of
overlapping green scales each shielding an ovary from which two
purple stigmas protrude. Wind-pollinated.
K(0-6) C 0 A 2-18 G 0
Female: K 0-6 C 0 A 0 / G(2)
The ovaries of the
female flowers are inferior. Fruit- fertilised
female catkins expand into club-shaped cone-like structures that
slowly disintegrate in autumn to release tiny (about 2 mm), easily
dispersed winged samara fruit. The fruit and seeds are tiny
and there are some 5.9 million seeds per kg in silver birch, and
8.45 million per kg in dwarf birch! The high numbers of seed that
can be produced per unit of resources and the ease with which birch
fruit disperse enables the rapid reproduction of
birch trees and allows them to exploit open spaces as pioneers.
Silver birch has whiter bark than downy birch, which ranges from silver-grey to brownish. On old silver birch trees, knobbly black bark replaces the white bark at the base of the trunk. Silver birches have hanging or weeping twigs, especially in ornamental varieties. The twigs of silver birch are smooth, those of downy birch are covered with short fine hairs.
The birch is a hardy tree occurring at higher altitudes than any other tree. Downy birch is the first tree to colonise areas on the edge of the Northern Ice Cap.
Yellow birch (B. alleghaniensis) –NE USA and SE Canada.
River or red birch (B. nigra) –S/E USA, occurs most commonly in wet or swampy soils in the southern USA.
Canoe or paper birch (B. papyrifera) -used by American Indians to build canoes.
B. albo-sinensis is found in the mountains of western China.
B. ermanii occurs in NE Asia and Japan.
Cherry birch (B. lenta) – eastern North America.
Japanese cherry birch (B. grossa) - Mountains in Japan.
Monarch birch (B. maximowicziana) – central and northern Japan.
Himalayan birch (B. utilis) -Mountains in China, Himalayas.
Above and below: Silver Birch, Betula pendula.Click all images for full size.
Below:The Birch Polypore (Piptoporus betulinus or Polyporus betulinus) or Razor Strop Fungus a bracket fungus that grows only on Birch trees. It can be found throughout the year and the brackets used to be dried and used to shrpen razors. This fungus grows only on dead birch trunks and is annual, although the brackets persist.
Article updated: 21/3/2014, 25/3/2020, 3/11/2020
Silver Birch - Betula pendula