Betula pendula

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. Silver birch can easily be confused with the similar downy birch (Betula pubescens). Yet, downy birches are characterised by hairy leaves and young shoots, whereas the same parts on silver birch are hairless. The leaf base of silver birch is usually a right angle to the stalk, while for downy birches, it is rounded. In terms of genetic structure, the trees are quite different, but do, however, occasionally hybridize. ==Distribution and habitat==

The silver birch grows naturally from western Europe eastwards to Kazakhstan, the Sakha Republic in Siberia, Mongolia, and the Xinjiang province in China, and southwards to the mountains of the Caucasus and northern Iran, Iraq, and Turkey. It is also native to northern Morocco and has become naturalised in some other parts of the world. 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 (C.K.Schneid.) Ashburner & McAll. – 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. ==Ecology==

The silver birch has an open canopy which allows plenty of light to reach the ground. This allows a variety of mosses, grasses, and flowering plants to grow beneath, which in turn attract insects. Flowering plants often found in birch woods include primrose (Primula vulgaris), violet (Viola riviniana), bluebell (Hyacinthoides non-scripta), wood anemone (Anemone nemorosa), and wood sorrel (Oxalis acetosella). Small shrubs that grow on the forest floor include blaeberry (Vaccinium myrtillus) and cowberry (Vaccinium vitis-idaea). Birds found in birch woodland include the chaffinch, tree pipit, willow warbler, nightingale, robin, woodcock, redpoll, and green woodpecker.-->) larvae feeding on silver birch, West Wales, July 2014 The branches of the silver birch often have tangled masses of twigs known as witch's brooms growing among them, caused by the fungus Taphrina betulina. Old trees are often killed by the decay fungus Fomitopsis betulina and fallen branches rot rapidly on the forest floor. This tree commonly grows with the mycorrhizal fungus Amanita muscaria in a mutualistic relationship. This applies particularly to acidic or nutrient-poor soils. Other mycorrhizal associates include Leccinum scabrum and Cantharellus cibarius. The larvae of a large number of species of butterflies, moths, and other insects feed on the leaves and other parts of the silver birch. In Germany, almost 500 species of insects have been found on silver and downy birch including 106 beetles and 105 lepidopterans, with 133 insect species feeding almost exclusively on birch. Birch dieback disease can affect planted trees, while naturally regenerated trees seem less susceptible. This disease also affects B. pubescens and in 2000 was reported at many of the sites planted with birch in Scotland during the 1990s. In the United States, the wood is attacked by the bronze birch borer (Agrilus anxius), an insect pest to which it has no natural resistance. ==Conservation==

Betula pendula is considered a species of least concern by the IUCN Red List. though it is now considered a synonym of B. pendula subsp. pendula. B. szaferi was previously considered extinct in the wild on the Red List, but is now considered a form of B. pendula with the presence of a mutant gene, causing it to grow weakly and fruit heavily. ==Uses==

The silver birch is Finland's national tree. Leafy, fragrant bunches of young silver birch boughs (called vihta or vasta) are used to gently beat oneself while bathing in the Finnish sauna. Silver birch is often planted in parks and gardens, grown for its white bark and gracefully drooping shoots, sometimes even in warmer-than-optimum places such as Los Angeles and Sydney. In Scandinavia and other regions of northern Europe, it is grown for forest products such as lumber and pulp, as well as for aesthetic purposes and ecosystem services. It is sometimes used as a pioneer and nurse tree elsewhere. The removal of bark was at one time so widespread that Carl Linnaeus expressed his concern for the survival of the woodlands. Birch brushwood is used for racecourse jumps and besom brooms. In the spring, large quantities of sap rise up the trunk and this can be tapped. It contains around 1% sugars and can be used in a similar way to maple syrup, being drunk fresh, concentrated by evaporation, or fermented into a "wine". Also present in the bark are other triterpene substances which have been used in laboratory research to identify its possible biological properties. Pharmaceuticals A standardized allergen extract from white birch, sold under the brand name Itulatek, is indicated in Canada as a sublingual agent to test for and limit allergic reactions to tree pollen from birch, alder and/or hazel in people with allergic rhinitis (with or without conjunctivitis). The combination of extracts from Betula pendula and Betula pubescens is approved in Europe to treat epidermolysis bullosa. ==Cultivation==

Successful birch cultivation requires a climate cool enough for at least the occasional winter snowfall. As they are shallow-rooted, they may require water during dry periods. They grow best in full sun planted in deep, well-drained soil. Cultivars and varieties • 'Carelica' or "curly birch" is called visakoivu in Finland. The wood is hard and burled throughout; it is prized for its decorative appearance and is used in wood-carving and as veneer. • 'Laciniata' • 'Tristis' The cultivars marked above have gained the Royal Horticultural Society's Award of Garden Merit. ==Gallery==

File:Breza na jesen.jpg|Tree in autumn File:Betula pendula winter.jpg|Tree in winter File:Birch-Betula-pendula-Tromsø.JPG|Betula pendula in Tromsø in May, Northern Norway Image:Betula pendula laciniata0.jpg|B. pendula 'Laciniata' File:HAZELIUS(1881) Vol.1, Abb.9, p037.jpg|A pair of Finnish traditional shoes woven from strips of birch bark == References ==