- Betula alba subsp. pubescens (Ehrh.) Regel
Downy Birch, Moor Birch, White Birch, European White Birch, Hairy Birch
No status defined
Value of species
Occurrence: Au, Be, Br, Bt, By, Cz, Da, Fe, Ga, Ge, Hb, He, Ho, Hs, Hu, Is, It, Ju, Lu, No, Po, Rf(C, CS, E, N, NW, S), Rm, Su, Uk(U) (Euromed, 2018).
A species of deciduous tree, native and abundant throughout northern Europe and northern Asia, growing farther north than any other broadleaf tree. It is closely related to, and often confused with, the silver birch (B. pendula), but grows in wetter places with heavier soils and poorer drainage; smaller trees can also be confused with the dwarf birch (B. nana).
Three varieties are recognised and it hybridises with the silver and dwarf birches. A number of cultivars have been developed but many are no longer in cultivation. The larva of the autumnal moth (Epirrita autumnata) feeds on the foliage and in some years, large areas of birch forest can be defoliated by this insect. A large number of fungi are associated with the tree and certain pathogenic fungi are the causal agents of birch dieback disease.
The tree is a pioneer species, readily colonising cleared land, but later being replaced by taller, more long-lived species. The bark can be stripped off without killing the tree and the bark and the timber is used for turnery and in the manufacture of plywood, furniture, shelves, coffins, matches, toys and wood flooring. The inner bark is edible and can be ground up and used in bread-making, as it still is at Easter in the traditional Finnish mämmi, or eaten in times of famine. The rising sap in spring is used to make refreshing drinks, wines, ales and liqueurs and various parts of the tree have been used in herbal medicine.
It is a deciduous tree growing to 10 to 20 m (33 to 66 ft) tall (rarely to 27 m), with a slender crown and a trunk up to 70 cm (28 in) (exceptionally 1 m) in diameter, with smooth but dull grey-white bark finely marked with dark horizontal lenticels. The shoots are grey-brown with fine downy. The leaves are ovate-acute, 2 to 5 cm (0.8 to 2.0 in) long and 1.5 to 4.5 cm (0.6 to 1.8 in) broad, with a finely serrated margin. The flowers are wind-pollinated catkins, produced in early spring before the leaves. The fruit is a pendulous, cylindrical aggregate 1 to 4 cm (0.4 to 1.6 in) long and 5 to 7 mm (0.2 to 0.3 in) wide which disintegrates at maturity, releasing the individual seeds; these seeds are 2 mm (0.08 in) long with two small wings along the side.
B. pubescens is closely related to, and often confused with, the silver birch (B. pendula). 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.
Downy birch can be distinguished from silver birch with its smooth, downy shoots, which are hairless and warty in silver birch. The bark of the downy birch is a dull greyish white, whereas the silver birch has striking white, papery bark with black fissures. The leaf margins also differ, finely serrated in downy birch, coarsely double-toothed in silver birch. The two have differences in habitat requirements, with downy birch more common on wet, poorly drained sites, such as clays and peat bogs, and silver birch found mainly on dry, sandy soils.
In more northerly locations, downy birch can also be confused with the dwarf birch (Betula nana), both species being morphologically variable. All three species can be distinguished cytologically, silver birch and dwarf birch being diploid (with two sets of chromosomes), whereas downy birch is tetraploid (with four sets of chromosomes). In Iceland, dwarf birch and downy birch sometimes hybridise, the resulting plants being triploid (with three sets of chromosomes).
The larva of the autumnal moth (Epirrita autumnata) feeds on the foliage of Betula pubescens and other tree species. In outbreak years, large areas of birch forest can be defoliated by this insect. Damage to the leaf tissue stimulates the tree to produce chemicals that reduce foliage quality, retarding the growth of the larvae and reducing their pupal weights.
In Greenland, about seventy species of fungi have been found growing in association with B. pubescens, as parasites or saprobes on living or dead wood. Some of the most common fungi include Ceriporia reticulata, Chondrostereum purpureum, Exidia repanda, Hyphoderma spp, Inonotus obliquus, Inonotus radiatus, Mycena galericulata, Mycena rubromarginata, Panellus ringens, Peniophora incarnata, Phellinus lundellii, Radulomyces confluens, Stereum rugosum, Trechispora spp., Tubulicrinis spp. and Tyromyces chioneus.
Birch dieback disease, associated with the fungal pathogens Marssonina betulae and Anisogramma virgultorum, can affect planted trees, while naturally regenerated trees seem less susceptible. This disease also affects Betula pendula and in 2000 was reported at many of the sites planted with birch in Scotland during the 1990s.
- Кузярін О.Т. Судинні рослини території торфовища "Білогорща” (м. Львів) // Наукові основи збереження біотичної різноманітності. - 2010. - Т.1(8), №1. - С.75-90.
- Alexander KUZYARIN, Dr, e-mail: firstname.lastname@example.org