Downy Birch, Betula pubescensIn Scotland sub-species pubescens occurs in the south and lowlands, while sub-species odorata is found in the Highlands. See also B. pendula. Sources of seed and plants Widespread in Britain from sea level to 800 metres, but is most common in the wetter, western side of the country; also plentiful in south-east England. Downy birch grows pure or in mixture with Black alder, Grey willow, Pedunculate and Sessile oak, rowan and Scots pine. Progeny testing shows that careful selection of parent trees can result in improved stem form and habit of growth, thus raising the value of Downy birch. Silviculture A light-demanding, pioneer species but tolerates more shade than Silver birch. It soon appears naturally on felled woodland sites. Soil types Prefers well-drained, sandy-loams but tolerates poorly-drained and acid soils with peat in the uplands and is found on the edges of fens, bogs and lakes. Rate of growth and yield Young trees grow quickly up to 20 years and provided the stem is persistent a slender crown is formed, but it does not grow as fast as Silver birch. The branches are more erect and secondary branches do not become pendulous. On poor, wet sites the apical dominance of the leading shoot is soon lost. Downy birch commonly attains heights of 15 metres in 30 years with stem diameters of 16 cms, and 18 to 20 metres in 50 years. Protection and resistance The rust fungus Melampsoridium betulinum is troublesome in the nursery and Polyporus betulinus is associated with the deterioration of old birches. Downy birch is hardy to late spring and early autumn frost. It is not often damaged by rabbits and grey squirrels. Used in shelterbelts because it is wind firm and withstands exposure. Downy birch is also moderately resistant to atmospheric pollution and so can be planted in towns and industrial areas to reclaim derelict land. Establishing and tending Requires care in transplanting and containerised plants should be used on difficult, reclaimed sites. Downy birch fruits freely and coppices strongly. Timber properties The timber of Downy birch is similar in all respects to that of Silver birch Amenity value The bark of older trees usually is grey white and the secondary branches are not pendulous, but the Downy birch is attractive and deservedly popular. Conservation The two birches support over 200 insect species so are important sources of food for birds. Timber value Used for furniture, turnery veneer and pulp. Posts are pressure treated with preservative and used for fencing. It is also a good firewood. Economic appraisal An under-rated and neglected species, especially in the uplands. A valuable improver of infertile sites and useful nurse for frost-tender species. As with Silver birch, extensive pure stands are not advocated but both birches are suitable for the edges of plantations and small groups through them. |
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