Black Alder, Alnus GlutinosaMany cultivars are available, including leaf variants. See also A. incana, A. cordata and A. rubra. Sources of seed and plants Grows naturally and has been planted throughout Britain, from sea level to 500 metres. The finest trees and stands are found in the Peak District of England. Good natural or seminatural stands of Black alder occur throughout Britain on wet ground overlying both acid rocks and limestones. Trees with strong buttresses and depressions in the stem below large branches should not be used as seed trees. Silviculture A light-demanding, pioneer tree usually found in pure stands, Black alder will grow in mixture with ash and birches and is a valuable nurse for oak and spruce on heavy clays. Soil types Remarkably tolerant of difficult soil conditions such as land that is marshy or liable to flooding, heavy clays and compacted soils ranging from acid to alkaline. The root nodules containing Frartkia spp. enable it to fix nitrogen. Rate of growth and yield Young trees grow quickly to 15 metres with whorls of short, upward-slanting branches to produce a conical crown. In woodlands the stem is straight and cylindrical. Black alder grows strongly for 25 to 30 years and the crowns then reach their full development. It commonly attains a height of 18 metres and stem diameter of' 30 cms but on fertile alluvial sites it will attain 27 metres height with stem diameter 120 cms. When grown for biomass Black alder can yield 8 to 10 dry tonnes per hectare per year on rotations of 15 to 20 years. Protection and resistance There are reports of dieback on heathland soils but the cause is unknown. Black alder is completely hardy to late spring and early autumn frosts. It is windfirm and can be used in coastal shelter belts because it withstands salt spray. It can be planted in industrial areas and because it is tolerant of alkaline conditions can be planted on pulverised fuel ash. Black alder is seldom damaged by grey squirrels. Establishing and tending Alder can produce adventitious roots and a11 common sizes of nursery stock establish well. It seeds regularly and coppices strongly. Timber properties A ring-porous wood with coarse texture, pale when first cut but soon darkening to red and then dries to light reddish-brown. The sapwood is not distinguishable from the heartwood. Generally straight grained, the timber is of medium density (530 kg/ml seasoned). It kiln-dries well and fairly rapidly and is good for turning, moderate for wood bending and satisfactory for staining and polishing. The heartwood is perishable but permeable to preservatives. Very durable under water. Amenity value Has been planted with good effect alongside motorways and on reclaimed land in industrial areas where its nitrogen fixing ability is valuable. Conservation Acts as host for 90 insect species. It can be used to fix riverbanks and check erosion Timber value A relatively light and soft wood, easy to work. Very suitable for general turnery, sawn wood and veneer; makes good charcoal but as a firewood is rather quickly consumed. Economic appraisal An adaptable, hardy and fast-growing tree suitable for upland sites where its windfirmness and tolerance of wet soils makes it useful in mixture with conifers and as a timber tree in pure stands along water courses. It should also be used more widely as a nurse for spruce and oak on clay soils in the lowlands. |
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