Often seen growing along rivers and streams, the alder's link to swamps, mystery and secrecy in a mythological sense is not surprising.
When Deirdre of the Sorrows of Irish mythology eloped with Naoise, son of Usna, they fled from Ulster to Alba (Scotland), to escape the wrath of King Conchobhar mac Nessa to whom Deirdre had been betrothed. They hid from the King's pursuing warriors in the alder woods of Glen Etibhe, where they eventually settled, and themes of hiding and secrecy connected with alder recur elsewhere in Celtic lore.
Perhaps these themes were derived from the particular atmosphere of alder woods. Where alders are not growing along rivers or streams, they form alder woods, or carrs, on wet or swampy ground. The wide bases of the alder trunks, from which small thickets of alder shoots may emerge, soon taper up to tall straight trunks, to expand into leafy canopies higher overhead.
Perhaps these woods, which in springtime can be mired in several inches of water, were seldom visited and as such made ideal hideaways. The green dye which can be derived from the flowers continued the hiding theme, being used to colour and thus camouflage the garments of outlaws like Robin Hood, as well as the clothes of faeries, to conceal them from human eyes.
Given the alder carrs' wet terrain and the risk of meeting bandits, boggarts or worse, it is not surprising that the Irish considered it unlucky to pass an alder tree on a journey. However, judging by the frequency with which the Gaelic for alder, fearn, crops up in place names in both Scotland and Ireland, there must have been a fair chance of such an encounter. The tree did make amends for this though, by providing its leaves which, when placed in shoes at the start of a long journey, would cool the feet and prevent swelling.
As befits a tree which grows primarily in swampy areas or by riversides, the alder's wood does not rot in wet conditions and indeed becomes as hard as stone when left immersed in water. People have made good use of this property since the Bronze Age at least, when crannochs (wooden strongholds on Scottish lochs) were built on rafts or piles of alder trunks. Such uses continued into the time of the Industrial Revolution when alder wood was favoured for the making of lock gates and other canal paraphernalia. Most of Venice is built on piles made of alder trunks.
Out of water and out of doors, however, the timber rots easily, and so it proved less suitable for building or fencing. It was similarly less than ideal as a fuel for heating, but it does make excellent charcoal. This burns with an intense heat and was used by the Celts, for example, to forge their best weapons. Later the charcoal was used in the manufacture of gunpowder, and because alder coppices easily, small plantations of the tree were often established next to such factories. In England alder was the preferred wood for clog making, possibly because it is a poor conductor of heat.
The living wood of alder is a pale colour but it turns a deep orange when cut. This gave the impression of bleeding and led to all sorts of negative superstitions about the tree. The deep colour fades with time to a paler, richer brown which was sought after by furniture makers, who gave alder wood its nickname of 'Scots mahogany'. However, if an English folk custom is to be believed, such furniture would have to be especially protected from wood worm - tradition suggested placing an alder branch in cupboards as a lure for wood worm. The parent beetle apparently preferred alder over any other wood as the place to lay her eggs.
Though looking to the future and not folklore as such, it is worth mentioning that alder is interacting with humanity in another way by helping us in today's climate of environmental destruction and restoration. The nitrogen-fixing nodules on the alder's roots improve soil fertility and so make this tree ideal for reclaiming degraded soils and industrial wastelands such as slag heaps.
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