Cones and catkins of the alder in winter

The Alder Generation

Tree correspondent Joan Taylor-Rowan, in her continuing exploration of trees is wowed by the hidden abilities of the unassuming alder.

Latin name: Alnus glutinosa
Common name: Alder, Common Alder
Location: St Helen’s Road side of the Buckshole reservoir, Hastings.

There are some people you come across who are inconspicuous and low-key. No-one quite recognises them or remembers their name and then one day you find out they’re a brain surgeon or a rocket scientist or Booker prize winner. Alder is the tree equivalent. It’s a nice enough tree – deciduous, rounded leaves, darkish catkins and discreet female flowers which develop into knobbly brown cones after wind pollination. The young twigs are sticky – hence the glutinosa. It’s found next to water or in damp marshy areas. In Hastings you’ll see a whole row of them bordering the Buckshole reservoir. They grow to a medium height (15-20m) and live for about 80 years.

So far, so underwhelming. However, the alder possesses not one but two genius abilities. The soft and porous wood, when immersed in water, doesn’t rot. Not only that, it actually gets harder. It can resist compression and decay for centuries. Because of this it was frequently used to make boats, water pipes and sluice gates. Sluice gates, I hear you yawn? It may not sound sexy, but it was to the Venetians. They recognised that this property could help them create the most beautiful and unlikely city on earth. Venice is almost entirely built on alder log pilings that have remained submerged, bearing the weight of palazzos, for centuries. In a process of selective draining of the swamps, sinking the pilings and then flooding, the Venetians constructed alder wood foundations on which to build their visionary city. Even the famous Rialto Bridge is supported by alder.

Venice. Photo by Henrique Ferreira, Upsplash

Fender Stratocaster. Photo by Jacek Dylag, Upsplash

Rather like Superman however, alder has a weak point. Once out of water, it loses its strength. Despite that, the wood is still used for another of humanity’s great inventions – musical instruments. People have carved flutes from alder branches for aeons, and since the 1950s alder has been the preferred wood for the body of the coveted electric guitar brand – Fender, because of its fine tonal properties.

But alder has a second genius property. Unusually for a tree, it is a nitrogen-fixer. I’m going to channel my inner Attenborough to explain what this means for those who’ve forgotten their school biology lessons – or bunked them. Alder has a symbiotic relationship (one where both parties benefit), with a bacterium, Frankia Alni. These bacteria live on the alder’s root system where they form large nodules – some as big as an orange – and turn (‘fix’) nitrogen from the air, into nitrates that feed the alder and the surrounding soil. In return, the alder shares the food it makes through photosynthesis. What this means for us, is that alder can rehabilitate barren or despoiled land such as slag heaps, brownfield sites and industrial wastelands. It’s usually the first to colonise such areas (a pioneer species) where it grows quickly, improving the soil and providing the conditions for other plants to follow.

Alder trees are a pioneer species offering shelter to many species.

But alder doesn’t just nourish the soil, its leaves are food for caddis flies and the larvae of the adorably named, alder kitten-moth, as well as many other invertebrates. These creatures then become food for fish. The alder roots cling to the river bank and spread into the water which helps to prevent soil erosion as well as giving shelter to waterbirds, and protection and shade to fish such as trout and salmon. It also provides perfect nesting areas for otters although I have not spotted any at Buckshole reservoir – yet.

The good insulating properties of alder wood made it the preferred material for clogs – and if your feet swelled on a long journey, alder leaves, placed in the shoes would soothe the feet. Alder branches were often placed in wooden cupboards to lure the woodworm away from the cupboard itself – it was believed that woodworm favoured alder over other woods. Aquarium enthusiasts interested in environmental issues, recommend the alder cones as an anti-fungal and anti-bacterial agent. They can lower the water pH and provide a healthier breeding environment for fish.

Alder bark yields an orange dye. Photo Mel Poole, Upsplash.

The flower cones of Alder provide a green dye – used in the past to camouflage forest dwellers like Robin Hood, and allegedly, the faeries. The outer bark of the alder yields a red/orange dye. Tannin-rich it has also been used to tan or cure leather. Alder famously made the best charcoal for gunpowder. Its force could send cannonballs further and faster. Most importantly, it could reach the high temperatures required for smelting iron. The Celts and later the Venetians, used it to manufacture their most-prized weaponry.

Like most trees I’ve researched there are myths and superstitions associated with alder. Although the Druids revered it, to others it had negative associations. Its thicketed, tangled nature and its preference for eerie marshy places gave it a sinister reputation. The Celts thought it an ill omen to pass one on a journey. The pale wood ‘bleeds’ dark orange when cut, a result of the high tannin content – which led to a belief that the souls of the ancestors were contained in the alder tree.

But you can’t please everyone. To my mind, alder has it all. It’s strong, resilient, musical, pioneering and a sharer – with perhaps just a touch of the brooding Heathcliff about it. If there was a Timber app – I’d be swiping right.

Read more of Joan Taylor Rowan’s tree guides here.

Also in: Green Times