Life

Take on Nature: The often overlooked alder is valuable to humans and to wildlife

An alder tree (Alnus glutinosa) in leaf with cones
Stephen Colton

THE fallen thrush's nest lay under a tall, dense conifer, its summer job done. Still a thing of beauty, this tidy structure of twigs, grass and moss, cemented together with an inner lining of mud, probably homed two or three broods during recent months.

Its spent presence pointed to autumn's coming, as do the ripening fruits of wild woodbine and the blackberries on arching bramble stems. Nearby small flocks of long-tailed tits fuelled the autumn feel as they flitted in search of food through birch, willow and that outcast of the woods, alder, Alnus glutinosa.

I paused my walk to observe this favoured tree of ancient druids seen along our rivers and streams, reflecting on how I have regularly failed to notice its charms, in favour of its more namely neighbours. Fearnóg in Irish, has been associated with war and death and, as such, an unlucky tree, best avoided.

Many of our ancestors feared the tree, not liking to fell it as the pale wood turns a reddish colour when cut, resembling blood. Ancient tales also tell us, though, how alder woods and their swampy environs made ideal hideaways. As Deirdre of the Sorrows and Naoise eloped from Ireland to escape the wrath of King Conchobhar mac Nessa, they hid from his warriors in alder woods by lough Etive, in Scotland.

The deranged Suibhne Geilt or Mad Sweeney, another king in early Ireland, who was cursed and condemned to a life of wandering by St Ronan, whom he insulted, wrote of the tree, "O alder you are not the enemy/ delightful is your hue/ you are not rending and prickly/ in the gap where you are". Maybe Sweeney felt an affinity with the alder as a fellow castaway.

The tree's roots which stretch far into our mythical past, have nitrogen-fixing nodules, containing a bacterium which absorbs nitrogen from the air, making it available to the tree, and also helping to improve the fertility of surrounding soil.

As a pioneer species, it can quickly colonise bare or disturbed ground and help other species follow. Its bark is dark and fissured, often covered in lichen, and its dark green racquet-shaped leaves are leathery with serrated edges.

Male and female flowers are found on catkins on the same tree, the male catkins yellow and pendulous, while the female catkins are green and oval shaped. Once pollinated they appear as tiny brown cones and remain all year. Alder wood is very durable in wet conditions and because it can withstand rot under water, it has been used for sluice and lock gates in canals, and sunken wooden piles. Much of Venice is built on piles made from alder trunks.

Historically, alder was also used for making shields, bowls, containers and charcoal, a component of gunpowder. Edward Wakefield (1812) noted that charcoal made from alder and willow was used in the manufacture of gunpowder near Cork in the early 1800s.

Peter Wise Jackson, in Ireland's Generous Nature (2014), refers to the work of John Teahan, Irish Furniture and Woodcraft (1994) which reveals that one of the oldest objects made from wood known in Ireland is a box made from alder dated to approximately 700 BC, discovered in Killymoon, near Cookstown, Co Tyrone in the early 19th century.

For all its various human uses through the centuries, the alder also remains a very valuable tree for wildlife, as an important food plant for the caterpillars of several moths and for its catkin seeds, a favourite food source for siskins, redpolls and goldfinches. Time to give the alder much more attention on future walks.

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