Pests and Diseases
The Grey Alder or Speckled Alder (Alnus incana) is an alder with a wide range across the cooler parts of the Northern Hemisphere. It is a small to medium size tree 15-20 m tall with smooth grey bark even in old age, its life span being a maximum of 60-100 years. The leaves are matt green, ovoid, 5-11 cm long and 4-8 cm broad. The flowers are catkins, appearing early in spring before the leaves emerge, the male catkins pendulous, 5-10 cm long, the female catkins 1.5 cm long and 1 cm broad when mature in late autumn. The seeds are small, 1-2 mm long, light brown with a narrow encircling wing. The Grey Alder has a shallow root system, and is marked not only by vigorous production of stump suckers, but also by root suckers, especially in the northern parts of its range.
The Grey Alder is a light-demanding, fast-growing tree that is very tolerant and 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 1500 metres. However, it does not require moist soil, and is a colonist of screes and shallow stony slopes. It is sometimes used for afforestation on non-fertile soils which it enriches by means of its nitrogen-fixing nodules. The wood resembles that of the common alder, but is somewhat paler and of little value.
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, mainly in the regions of the Alps, Carpathians and the Caucasus.
- Alnus incana subsp. hirsuta (A. hirsuta; Manchurian Alder). Northeastern Asia, and central Asia in mountains.
- Alnus incana subsp. kolaensis. Subarctic northeast Europe.
- Alnus incana subsp. oblongifolia (A. oblongifolia; Arizona Alder). Southwestern North America.
- Alnus incana subsp. rugosa (A. rugosa; Speckled Alder). Northeastern North America.
- Alnus incana subsp. tenuifolia (A. tenuifolia; Thinleaf Alder or Mountain Alder). Northwestern North America.
Several species of Lepidoptera use Grey Alder as a food plant for their caterpillars. See w:List of Lepidoptera that feed on Alders.