Alnus glutinosa
Alder, common alder, black alder, European alder
Irish name: Fearnóg
Latin name: Alnus glutinosa
Family: Betulaceae
Origin: Native
Tree type: Deciduous broadleaf tree
How it looks
Shape, bark, twigs
A cone-shaped tree, it can grow to a height of around 28m. Younger alder trees display olive-green bark with noticeable lenticels structures for gas exchange. As they age, the bark changes to a greyish-brown colour and becomes rough, forming cracked square plates. The twigs are light brown with a spotted stem that turns red towards the top.
Buds
Buds are positioned on short stalks and alternate along the stem. They are round but flattened, resembling paddles. They measure 6-9mm in length, are covered in fine hair, and are a soft purple/grey colour.
Leaves
The dark green leaves are racquet-shaped and have a leathery texture. They have toothed margins, with fewer teeth near the leaf stalk (petiole). The leaf tips are not pointed and are often notched. In the autumn, the leaves turn brown and dry before falling.
Flowers
Alder trees are monoecious, with male and female flowers on the same tree. They flower between February and April before the leaves appear. The flowers are found on catkins. The male flower is a long catkin, about 5-10cm long, turning yellow as it releases pollen. Female flowers are small, green, oval-shaped catkins, usually grouped in clusters of three to eight on each stalk.
Fruits
After pollination by wind, female catkins gradually become woody and appear as small brown cones in winter. They typically open in October to release their seeds. The seeds are flat and waxy, with two wings containing air bubbles, allowing them to float and be carried away by water. The cones often remain on the tree long after the seeds have dispersed in winter.
Similar species
The rounded leaf shapes are similar, but hazel leaves are softly hairy compared to the shiny ones of alder.
Where to find it
Alder is one of Ireland’s most widely distributed trees and is known for its adaptability. It is a fast-growing tree that can thrive in challenging conditions, including poor, saturated soils and strong winds, making it highly resilient. You can find alder trees alongside freshwater lakes and riverbanks, where their robust, fibrous roots play a role in stabilising the banks.
Alder is not limited to wet areas; it can also grow in drier locations. It sometimes appears in mixed woodlands, on the edges of forests, and can readily colonise open, bare ground. Alder has the ability to obtain nutrients through a process known as nitrogen fixation. It forms a symbiotic relationship with the bacterium Frankia alni, which captures nitrogen from the air. These bacteria reside in nodules on the tree's roots, enabling alder to thrive in nutrient-poor soils where many other trees struggle.
Alder is native to almost all continental Europe, with the exception of the far northern and southern regions.
Cultural importance
History | Myth | Literature
History
Archaeological excavations undertaken throughout Ireland demonstrate that alder was widely used for a range of purposes from the Mesolithic period (c. 8000-4000 BC) onwards. For instance, a number of 7000-year-old fish traps made from alder were recovered from excavations in Clowanstown, County Meath. Excavations carried at Edercloon, Co. Longford in 2006 discovered that alder had been used during the Bronze and Iron-Age (c. 800 BC-400 AD) to construct trackways for traversing the bog or accessing its resources. Other alder artefacts recovered from the site included bowls, domestic vessels, tubs, troughs, tool handles, wooden block wheels and wheel rims.
A number of stylised, anthropomorphic Bronze-Age idols made from alder have been found in Ireland, the most famous being the Kilbeg figure, also known as the ‘Red Man of Kilbeg’, which was deposited in Ballykean bog, Co.Offaly somewhere in the date range of c. 1740–1531 BC, and is thought to be a votive offering, representing a ritual sacrifice. Michael Stanley suggests that alder may have been used purposely to craft this idol on account of the red droplets that ooze from the wood when cut, giving the impression of human bleeding. Alder may have been used to symbolise death in this instance.
Alder also seems to have been used for ritual purposes at other locations during the Iron-Age. It has been suggested that the Pallasboy vessel, a large, intact, elder trough, found in Toar bog, Co. Westmeath in 2000, may have had ceremonial significance both during its lifetime and when it was deposited. Elsewhere, on the Iron-Age site of Raffin Fort, Co. Meath, alder twigs appear to have been burned as part of ritual practices carried out at the site.
In early Medieval Ireland (c. 400-1100), alder was considered one of the ‘Commoners of the Wood’. Thus, while not as valuable as the ‘Nobles of the Wood’, such as the oak, it was still prized, as Fergus Kelly reveals, for its use in the manufacture of ‘shields, masts and tent-poles'. The bark of the alder was traditionally used to tan leather and to make black dye. Furthermore, evidence from archaeological excavations demonstrates that alder was also used to construct the foundations of crannógs (man-made lake island dwellings) during this period. As Kelly relates, alder, being one of the ‘commoners of the wood’, was considered so valuable that:
The penalty-fine for damage to any of these trees is a milch cow...the payment of another milch cow as compensation for base-cutting, a yearling heifer for fork-cutting, and a sheep for branch-cutting. If the tree is completely extirpated (aurbe), a payment of two milch cows and a three-year-old heifer is due. (Kelly 1999, 44)
The inclusion of alder in the ogham alphabet also points to its significance during this period, with its old Irish name, ‘fern’, standing for the ogham character or letter ‘f’:
Myth, Legend and Folklore
Niall MacCoitir explains that according to an old Irish tradition, it was believed that the first man ‘sprung’ from an alder. However, he advises that, at the same time, alder was generally seen as an unlucky tree. Similar to some of the historical references above, MacCoitir suggests that in various European traditions, alder is associated with death, likely on account of the way it appears to bleed and turn from white to red when cut. It is also widely associated with war, perhaps for the same reason, but also due to the fact that, historically, alder was used to make shields. The red shields that often appear in Irish myths may point to this. MacCoitir proposes that the red branch referred to in the name of the ‘Red Branch Knights’ who appear in the Ulster myths, may represent alder. Alder is also thought to be linked with Donn, the god of the underworld.
Literature
Alder features in early Medieval Irish poetry and texts. Contrary to its negative associations, in early the Irish poem, The Madness of Sweeney, it is hailed as ‘delightful’. William Butler Yeats writes about the druidic spell-casting properties of alder in his poem, The Death of Cúchulainn. Séamus Heaney also celebrates the tree in his poem, Planting the Alder.
Value to wildlife
Alder plays a vital role in supporting wildlife. It serves as the primary food source for the caterpillars of various moth species, such as the pebble hook-tip and the blue-bordered carpet moth. The catkins produced by alder offer an early supply of nectar and pollen, making them a valuable resource for bees and other pollinators. Additionally, the alder seeds are enjoyed by birds like the siskin, redpoll, and goldfinch.
Alder is particularly well-suited for growth in wet and humid environments, creating favourable conditions for mosses, lichens, and fungi, which often cover the tree. Beyond this, alder contributes to soil fertility by its ability to fix nitrogen, which, in turn, enhances conditions for the growth of other plant species.
The extensive root system of alder trees plays a crucial role in stabilising riverbanks and preventing soil erosion. This stability provides a supportive habitat for diverse wildlife, including otters and kingfishers, along riverbanks and lakesides.
Threats
Since the new millennia, the alder tree has faced a significant threat from the pathogen Phytophthora alni, which typically infiltrates the tree through its root system. This pathogen has been observed across Europe and has recently been identified in Northern Ireland. This detection signals the potential spread of the disease throughout Ireland, endangering numerous alder populations. Ireland has witnessed various symptoms of this disease, such as the thinning of tree crowns, the presence of bleeding trunk cankers, and, in some cases, the death of alder trees.
To learn more about threats to Irish trees, visit ‘Threats to Trees.’
Uses
In ancient Ireland, sections of alder timber served as round shields. Later, it found applications in crafting clogs and in the furniture industry. Interestingly, it was believed that female woodworms preferred laying eggs in alder wood over other types. As a preventive measure, alder branches were traditionally cut and placed in cupboards to deter woodworms from infesting the cupboard timber.
Alder wood, being soft and porous, maintains durability when kept wet. This characteristic makes it suitable for crafting sluice gates, constructing bridges, and creating underwater foundations along streams, rivers, and canals. Presently, alder wood is used to produce timber veneers, pulp, and plywood. Alder's ability to regenerate well when coppiced makes it an excellent charcoal and gunpowder production source. It is also frequently used for smoking food items.
After gently simmering alder bark in water (decocted), it can be applied externally to address various skin conditions. Alder bark tea can be drunk for mouth ulcerations and sore throats. The leaves can lessen swelling and pain. They are used to soothe sore throats and were historically used to alleviate breast swelling in nursing mothers. Additionally, the young male catkins can be sucked to relieve a sore throat.
References
Kelly, F. 1999. Trees in Early Ireland, Augustine Henry Memorial Lecture 11th March 1999, Irish forestry: Journal of the Society of Irish Foresters, 56, 39-57.
Literature and Ireland’s Trees. 2023. Literature and Ireland’s Trees. Online: LIT: Literature and Ireland's Trees (litliteratureandirelandstrees.com)
MacCoitir, N. 2015. Ireland’s Trees: Myths, Legends and Folklore. Cork: The Collins Press.
McMahon, P. 2023. Island of Woods: How Ireland Lost Its Forests and How to Get Them Back, Dublin: New Island Books.
Moore, C. 2015. Alder, Why the Tree of Death?, The Pallasboy Project Blog. Online: Alder, why the tree of death? | The Pallasboy Project (wordpress.com)
Moore, C. 2021. Between the Meadows: The archaeology of Edercloon on the N4 Dromod–Roosky Bypass: 11 (TII Heritage), Dublin: Transport Infrastructure Ireland.
Neeson, E. 1991. A History of Irish Forestry, Dublin: The Lilliput Press Ltd.
Stanley, M. 2006. The ‘Red Man’ of Kilbeg: And Early Bronze Age Idol from County Offaly, PAST: The Newsletter of the Prehistoric Society, 52. Online: Prehistoric Society - Past No. 52 (ucl.ac.uk)
A-Z of British trees. Woodland Trust. Retrieved 11 April 2024, from https://www.woodlandtrust.org.uk/trees-woods-and-wildlife/british-trees/a-z-of-british-trees/
Native Irish Trees. Tree Council. Retrieved 11 April 2024, from https://www.treecouncil.ie/native-irish-trees
Stroh, P. A., Humphrey, T. A., Burkmar, R. J., Pescott, O. L., Roy, D. B., & Walker, K. J. (2023). BSBI Online Plant Atlas 2020. https://plantatlas2020.org/atlas