Identifying characteristics:
Young trees have a pyramidal crown, becoming ovoid when older and growing
to 60 feet tall or more. Trees are often multistemmed and shrubby in the
wild. The 2- to 5-inch-long leaves
are simple, alternate and nearly round, with 6 to 8 pairs of parallel veins
and coarsely-toothed, doubly-serrate margins. Leaves notably lack a terminal
point. Foliage is a dark, glossy green above, paler, with tufts of axillary
hairs below, and shows little coloration in autumn. Male and female flowers occur on the same plant early
in spring, before the leaves appear. Male catkins are reddish-brown, occuring
in groups of 3 to 5. Female flowers are produced in purplish, elliptical
cones in March. Numerous fruits, or
small, winged nutlets, mature in a woody, 0.75-inch-long cone, and are released
in late autumn. Cones persist on the tree through winter. Stalked, ovoid
buds to 0.5 inches long are enclosed in two purplish-red scales that
meet along their edges but do not overlap. Bark
is smooth and grayish-green with white lenticels, becoming dark brown and
lightly furrowed.
Similar species:
- Speckled alder (A. rugosa) and other native alders
Ecology:
Distribution: Native to Europe (including Britain), Northern Asia
and northern Africa, the European alder has escaped cultivation and become
naturalized in eastern Canada and the US.
Habitat: Although commonly found in low, wet, swampy areas (even surviving in water), this species also performs well in dry sites. It often colonizes waterways by seeding. It occurs from zone 3 to 7, but is the least suitable alder for hot, humid regions. It tolerates full sun or partial shade, as well as acid or alkaline soils. As alders are more susceptible to pests than diseases, this species is subject to few diseases in cultivation, and it seldom suffers foliage damage by either agent. Alders are a preferred host of the gypsy moth and are host to the fall webworm (which attacks ash trees). Female cones are sometimes damaged by powdery mildew. Tent caterpillar can be a threat, and cankers and leaf rust may occur, but are less serious.
Uses:
Wood: The European alder has recently come to be considered a useful
nurse tree for more valuable timber trees, and as a source of wood
for pulp and furniture.
Wildlife: Some birds eat the buds and seeds (redpolls, siskins and goldfinches), and gamebirds and hoofed browsers feed on other parts of the plant. Dense colonies of alders provide cover for many species of wildlife.
Horticulture: With attractive cones and male catkins, this alder is sometimes planted in Iowa as an ornamental. The native alders, being more disease-prone and less attractive, have perhaps tainted the reputation of this genus. European alder is good for exceptionally wet areas along ponds and streams, and is widely planted in Europe. 'Pyramidalis' is a form with a columnar habit, to 50 feet tall; 'Laciniata' has finely-cut leaves; and 'Imperialis' has finer-cut leaves than 'Laciniata'. The red alder (A. rubra) is a tree to 40 feet tall, and is native to the Pacific Northwest. The speckled alder (A. rugosa), with crooked, twisted branches, is native to northeast Iowa and grows to 30 feet tall.
