Common Name Sitka alder
Form Medium tree
Origin N Europe & NW Asia
Moisture wet to mesic
N fixing yes (no data)
There are four to six subspecies, some treated as separate species by some authors. There are four to six subspecies, some treated as separate species by some authors:
- Alnus incana subsp. incana (Grey Alder). — Northern Europe and northwestern Asia, and central and southern Europe in mountains.
- Alnus incana subsp. hirsuta; Manchurian Alder. — In mountains of Northeast Asia and Central Asia.
- Alnus incana subsp. kolaensis — Subarctic northeast Europe.
- Alnus incana subsp. oblongifolia; Arizona Alder. — Madrean Sky Islands of southwestern North America, in Arizona, New Mexico, and Northwestern Mexico.
- Alnus incana subsp. rugosa; Speckled Alder. — Northeastern North America, including the Northeastern United States.
- Alnus incana subsp. tenuifolia (Nutt.) Breitung (=A. tenuifolia Nutt.); Mountain Alder, or Thinleaf Alder. — Western North America, including New Mexico to California and Alaska.
Alnus incana is a light-demanding, fast-growing tree that grows well on poorer soils. In central Europe, it is a colonist of alluvial land alongside mountain brooks and streams, occurring at elevations up to 1,500 metres. However, it does not require moist soil, and will also colonize screes and shallow stony slopes. In the northern part of its range, it is a common tree species at sea level in forests, abandoned fields and on lakeshores. It is sometimes used for afforestation on non-fertile soils which it enriches by means of nitrogen fixing bacteria in its root nodules.
Its fast rate of growth means that it quickly provides sheltered conditions to allow more permanent woodland trees to become established. Alder trees also have a heavy leaf canopy and when the leaves fall in the autumn they help to build up the humus content of the soil. Alder seedlings do not compete well in shady woodland conditions and so this species gradually dies out as the other trees become established. The bark and the fruits contain up to 20% tannin. Wood - light, soft, fairly elastic, easy to split. Used for clogs, bowls, woodcuts etc. Much valued by cabinet makers.