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Last edited 04 Oct 2022

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Alder wood in construction

1 Introduction
2 Forestry products
3 Specification
4 External links
5 Related articles on Designing Buildings

[edit] Introduction

Alder (Alnus glutinosa) is grown in the UK, and Europe, used for minor utility products, sometimes available as beams.

It is native to almost the whole of continental Europe (other than the far north and south), with over 30 species in the genus Alnus. It can also be found in the Americas. The species A. glutinosa is the only one in the genus that is native to the UK.

Alders are part of the birch family (Betulaceae), but a different genera, Alnus whilst birches are of the genus Betula. It is monoecious, which means both male and female flowers or catkins are found on the same tree. Male catkins turn yellow whilst female catkins are a green, oval shape that resembles woody, tiny, cone-like fruits after pollination.

Alder grows well in moist ground near water as it thrives in damp, cool environments. The roots can help prevent soil erosion near streams, growing in marshes and wet woodlands. It can also grow in drier areas on the edges of mixed woodland, as it grows well seeded on bare ground. In wet habitats alder combined with moss, lichen and funghi, is important for moths, caterpillars, butterflies, and otters living in the roots, whilst the birds siskin, redpoll and goldfinch feed on the catkins that also provide an early source of pollen for bees.

The Grey Alder (Alnus incana) is planted in gardens and for shelter and can reach heights of up to 80ft. Although it prefers moist ground it does not tolerate water logging in the same way as the Common Alder. It is a hardier species, often used on reclaimed industrial land. This species produces highly ornamental catkins before the Common Alder and before its first leaf flush.

According to ancient belief / superstition, evil lurked in the Common Alder, because its wood appears to bleed when cut, it was feared, suggesting the tree was a malign spirit embodied.

[edit] Forestry products

As a forestry crop it has the advantage of the nitrogen-fixing bacterium Frankia alni at its roots, so it can be grown in wasteland areas with poor soils, able to improve soil quality as a pioneer species. All alders have this ability, with certain species such as the Italian Alder (Alnus cordata) being particularly effective. Alder also coppices well and is used to produce charcoal. Charcoaled Alder Buckthorn (Frangula alnus) was historically used in the production of gunpowder.

As a wood it is soft, porous and light brown in colour becoming more red with age, it is non-durable due to poor resistance to decay, however, it can be durable if kept wet, as it can withstand rotting in water. As such it has historically been used for boat construction, in sluice gates and water pipes. Today, alder wood is mainly used to make timber veneers, pulp and plywood, although some interior furniture may be made from alder as it is relatively easy to work with and has an attractive finish. Traditionally, alder branches might have been cut and placed inside cupboards to deter woodworm from laying eggs in the timber of the cupboard.