Oct 1, 2009

Alnus incana (Alder) Betulaceae (Birch Family)

Alder is a common tree along watercourses, damp ditches and other wet habitats. The male catkins are superficially similar to those of hazel, but rather more reddish. The long male catkins produce the pollen, which is carried on the wind to the smaller, red female flowers seen above them (which are not reminiscent of hazel). After pollination these female flowers develop into small, woody cone-like fruits which persist on the branches for some time, which makes alders easy to recognise and identify!

Alder is an attractive, low-growing tree common along streams. Its leaves are toothed and often folded inward along the central leaf vein. Alder has small persistent cones which are actually remains of the staminate flower clusters. These remain on the branches after the leaves have fallen. Alder almost always has many slender trunks.

"Alnus" is the ancient Latin name for the tree, and "incana" is Latin for "gray or hairy".

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 and 5-10 cm long, the female catkins 1.5 cm long and one cm broad when mature in late autumn. The seeds are small, 1-2 mm long, and 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. Th e woo d resembles that of the black alder, but is somewhat paler and of little value.


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 1500 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. Several species of Lepidoptera use Grey Alder as a food plant for their caterpillars. In the Boreal forest area of Canada, A. incana is often associated with Black Spruce in the forest type termed Black Spruce/Speckled Alder.

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