Alnus glutinosa, the Common or European Alder, is a native of Europe, from south of the Arctic Circle down to North Africa and east wards into Asia. Introduced elsewhere. If you meet an Alder tree, you are bound to be close to water, for they like damp places such as marshes, riversides, lakesides, and wet woods. Its tiny roots seem to attract moisture, so it is often boggy or soggy soil around it. Extensive agricultural drainage schemes have made this cousin of the birch and hazel less abundant than it once was, but it is still very common. The tree used to be coppiced for the gunpowder industry. Alder trees are often used in land reclamation schemes, especially the Grey Alder (A.incata). Alders are helped in their colonisation of damp by their ability to form adventitious roots, similar to the stilt roots of certain tropical trees.
grows up to 20 meters high, but it often appears as a shrub. The young trees
grow very fast and can gain up to half a meter each season. They can be said to
be mature when about 60 years of age and have a lifespan of about 150 years.
Uncoppiced trees have tall trunks, narrow crowns.
Alder is an interesting tree with some unusual characteristics. It is the only deciduous (non-evergreen) tree which has tiny cones to bear its seeds. They are in fact the female catkins of the tree and they make Alder easy to recognise in winter. Its branches are not bare as so many of our other deciduous trees, because the winter branches are crowded with immature catkins and old empty seed-cones. The flowers are catkins formed in the year before ripening. The male flowers are drooping cylinders and the female catkins look like tiny cones.
On closer observation we find that the leaf buds are sheathed in purplish scales with a light misty bloom on it, very much like red grapes have. Each bud has its own bud stalk, also unusual in trees, and are arranged in a spiraling fashion around the branch.
Many of the young trees have a conical shape, vaguely reminiscent of conifers, but as the tree matures it tends to have a more open straggly crown. In the past Alder used to be grown extensively in coppices, which means that the wood is harvested every 6 -12 years in the winter, which leaves the bole to produce new growth in the spring. The wood was then turned into a high quality charcoal, much valued as gun powder for its property of igniting very reliably and easily.
The leaves are roundish with a characteristic indentation where one would expect the tip of the leaf to be, like the top of a heart-shape. During the summer these leaves darken to a deep green and their tops are quite shiny and leathery.
Alders have an extra-ordinary ability to resist the decaying influence of water. Its timber is almost indefinitely rot proof in a wet environment and its trunks are the foundation of much of the glory of Venice and the graceful houses lining the canals of Amsterdam. Its shiny leathery leaves resist the onslaught of the wet autumn and early winter rains far better than any other deciduous tree. The leaves do not colour in the autumn, just become darker and wither to brown or black and often can be found on the branches as late as December! Its tiny seeds have two corky wings, containing air bubbles, which helps them to float on water in their search for a place to settle.