Betula pendula, commonly known as silver birch, warty birch, European white birch, or East Asian white birch, is a species of tree in the family Betulaceae, 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 the European white birch or weeping birch and is considered invasive in some states in the United States and parts of Canada.
The silver birch is a medium-sized deciduous 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 with doubly serrate margins and turn yellow and brown in autumn before they fall. The flowers are catkins and the light, winged seeds get widely scattered by the wind. The silver birch is a hardy tree, a pioneer 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 its canopy. 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 in traditional medicine and the bark contains triterpenes, which have been shown to have medicinal properties.
Description
thumb|left|upright|Silver birch
thumb|right|upright|Silver birch has often pendulous twigs, after which the tree has received its scientific name.
The silver birch typically reaches tall, exceptionally up to , Some shoots are long and bear the male catkins 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. The small, 1- to 2-mm winged seeds ripen in late summer on pendulous, cylindrical catkins long and 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. 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, acidic soils and is found on heathland, mountainsides, and clinging to crags. Its tolerance to pollution make it suitable for planting in industrial areas and exposed sites. It has been introduced into North America, where it is known as the European white birch, and is considered invasive in the states of Kentucky, Maryland, Washington, and Wisconsin. It is naturalised and locally invasive in parts of Canada.
Taxonomy
Three subspecies of silver birch are accepted:
- Betula pendula subsp. szechuanica <small>(C.K.Schneid.) Ashburner & McAll.</small> – western China, from Qinghai and Gansu to Yunnan and southeast Xizang (Tibet), treated by some botanists as Betula szechuanica The two have differences in habitat requirements, with silver birch found mainly on dry, sandy soils, and downy birch more common on wet, poorly drained sites such as clay soils and peat 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 name B. pendula of the other species), but they are regarded as distinct species throughout Europe.