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Features

Tree

Leaf

Blossom

Fruit

  Latin name Alnus incana
  Family Betulaceae (birch family)
  Distribution Europe to the Caucasus, widespread in Central Europe
  Height 10 to 20 m
  Age Up to 60 years
  Roots Heart root system with robust horizontal roots
  Bark Light grey, smooth, covered with many cork warts, even in old age rarely cracks.
  Leaves Alternate, broad and ovate, clearly pointed, upper side dark green, underside covered with white-grey fuzz. Have prominently protruding leaf veins and doubly serrated margins.
  Flowers Monoecious; male flowers in hanging catkins, female catkins inconspicuous, round cones; they form in the previous year and overwinter. Wind-pollinated.
  Flowering period February to March
  Fruits Ellipsoid, grey-brown fruit cones up to 1.5 cm long with 3 to 4 mm small, narrowly winged, single-seeded nut fruits
  Fruiting period From September
  Alternative names White alder

 

Alnus incana

The grey alder belongs to the birch family (Betulaceae) and is a multi-stemmed tree, 6 to 15 metres, rarely up to 25 metres high with a dense, initially conical, later round crown. Its shallow roots are very dense and produce plenty of root sprouts in the surrounding area. In natural habitats, grey alders propagate both vegetatively through its root sprouts . The ripe fruits fall out of the cones during the winter months and, provided with a narrow wing margin, spread by wind (anemochory) and water (hydrochory).

The grey alder is involved in various symbioses, as for instance with the bacterium Frankia alni. As a result, the tree generates root nodules, in which the nitrogen from the air is fixed and thereby made available to the plant. This increases the nitrogen content of the leaves, and with their decomposition, the concentration of nitrogen compounds in the soil, leading to improvement of the soil quality. This is one of the reasons why the fast-growing grey alder is frequently used for reforesting spoil heaps as well as stabilising slopes and embankments.

The grey alder is also involved in root symbioses (ectomycorrhiza) with various species of soil fungi, including Gyrodon lividus and Paxillus involutus. Their thread-like cells (mycelium) form a dense sheath around the young root ends, thus creating a network for nutrient exchange between fungus and tree. The hyphae of the fungus take over the task of the missing root hairs. They extend far into the soil matrix, ensuring comprehensive nutrient and water uptake. In addition, the mycorrhizae protect the tree roots from infections by preventing the penetration of other bacteria or fungi.

Ecology

Thirteen moth species, such as the large alder dagger (Acronicta cuspis) or the scarce conformist (Lithophane consocia), use the grey alder as larval food. For birds, especially for the rare hazel grouse, the winter buds and male catkins are important winter food.

Wood

The soft and moderately heavy wood of grey alders is less durable than the wood of their close relatives, the black alders. In addition, their stems are usually much thinner and often crooked or twisted due to their almost shrub-like growth. Therefore, grey alder wood is mainly used for chipboard, fiberboard and paper production.