Crooked Run Valley
European black alder (Alnus glutinosa)
European black alder
Alnus alnus (L.) Britton
Alnus vulgaris Hill
Betula alnus L. var. glutinosa L.
CONFIRMATION STATUS: Confirmed.
TAXONOMY: The current accepted scientific name for European alder
is Alnus glutinosa (L.) Gaertn.
NATIVE STATUS: Introduced, United States and Canada.
GENERAL BOTANICAL CHARACTERISTICS: European alder is a
medium to large tree (rapid to medium growth rate) with a very narrow,
upright crown. In its native habitat it reaches 60 feet tall by 30 feet in
diameter at maturity, although it rarely gets very large in North America.
It generally has an upright pyramidal growth habit in youth, becoming up-
right oval or open and irregular with maturity, sometimes losing its strong
central leader with age, and also sometimes found in multitrunked form.
The bark is green-brown in youth and is initially smooth, changing to brown
and slightly ridged or with small broken patches with maturity. Twigs are
green to brown, smooth and sticky when young, later turning greenish
brown; buds are stalked, purplish brown in color and somewhat three
sided. Leaves are alternate, simple, oval to orbicular, 2 to 4 inches long,
2 to 3 inches wide, rounded or slightly notched tip, with a doubly serrated
margin, dark green above, lighter below with some scruffy pubescence in
vein axils. Like most members of the Birch Family, the leaves of European
elder flutter in the slightest breeze, due to its broad leaf blade base and the
relatively long petiole. Fall color is green, chartreuse, or yellow-brown.
Flowers are monoecious - males slender, reddish-brown catkins (1 to 1 1/2
inch long), much longer when shedding pollen; females small (1/6 inch)
reddish-brown, cone-like catkins in clusters near branch tips. The fruit is
cone-like woody catkin, initially green, turning brown when ripe, 3/4 inch
long, egg-shaped, containing many small winged nutlets, persistent through
REGENERATION PROCESSES: European alder propagates primarily
by reseeding; as an ornamental, it can be propageted by rooted stem
cuttings, while the cultivars are propagated by rooted stem cuttings or
cuttings grafted onto species rootstock. European alder commonly sprouts
from the stump after cutting, and live branches can be layered successfully.
European alder seeds have no wings; therefore, despite their small size
they are usually not spread more than 30 to 60 in (100 to 200 ft) by the
wind, although they may occasionally be blown much farther over the top
of crusted snow. Where wind is the only likely means of dissemination,
alder saplings are rarely found more than 20 to 30 in (65 to 100 ft) from
the parent tree. The seeds contain an air bladder and float in water; run-
ning water and wind drift over standing water are may be the principal
agents of dispersal.
SITE CHARACTERISTICS: European alder prefers moist to wet soils
of average fertility in full to partial sun, but is adaptable to poor soils, dry
soils, and soils of various pH.
SUCCESSIONAL STATUS: European alder is primarily a pioneer and
opportunist species, and is capable of direct colonization of even the rawest
of soil material. The species acts as a pioneer, being capable of colonizing at
very early stages in the primary succession if good seed is available. Alder
carr (deciduous woodland or scrub on a permanently wet, organic soil) does
not succeed an earlier Salix and Rharnnus carr, though these species may
colonize simultaneously, and pure alder carr eventually results from the
greater vigour and longevity of the alders.
Alder has generally beneficial effects on associated plants. Part of the nitro-
gen fixed by alders soon becomes available to other species in mixed stands,
especially through mineralization of nitrogen leached from litter.
SEASONAL DEVELOPMENT: Clustered reddish-brown male catkins
are present in winter, to about 1" long, but elongate up to 4" in March, sway-
ing in the early spring winds. Miniature oval purple female flowers are barely
noticeable in March. The clusters of opened fruits turn brown in autumn
and are winter-persistent.
GENERAL DISTRIBUTION: European alder has a broad natural range
that includes most of Europe and extends into North Africa, Asia Minor,
and western Siberia. Densest distribution is in the lowlands of northern
Germany, northern Poland, White Russia, and the northwestern Ukraine.
The species is locally naturalized throughout the northeastern United
States and maritime Canada.
SKY MEADOWS DISTRIBUTION:
Tree specimens can be found on trails marked in red.
Appalachian Trail/Old Trail
South Ridge/North Ridge
Rolling Meadows/ Lost Mountain
The specific distribution of European alder has not been determined.
HABITAT TYPES AND PLANT COMMUNITIES: European alder
is generally found in moist to wet situations, such as streambanks, flood-
plains, and wetland edges. It is known to be locally invasive and can be an
aggressive species in the early successional stages.
Natural alder communities include ash, birch, willow, and oak, and, as one
researcher has observed, "forms ash-alder wood[land] on low-lying ground
of high soil fertility and moisture, alder-willow thickets in areas liable to sea-
sonal flooding, and alder-birch wood on higher lying, less fertile, generally
acid soils. Pure stands are common, but not as extensive in Britain as, for
example, in northwest Germany". European alder and gray willow, Salix
cinerea atrocinerea, form a tidal woodland near the upper limits of a salt
marsh on the Cornish coast. In the absence of disturbance, the alder-
willow community succeeds the marsh.
IMPORTANCE AND USES: European alder is valuable for wildlife.
Because the cones open gradually and release seed throughout the winter,
they are a dependable source of food for seed-eating birds such as pine
siskins and goldfinches. European alder is recommended for use in shelter-
belts to provide cover for pheasants. When combined with Prunus
laurocerasus and Sorbus aria it makes a compact planting suitable for
establishment adjacent to cropland.
Alders have been recommended for afforestation of disturbed areas
throughout much of the temperate world. Their tolerance of low pH and
their rapid growth, abundant leaf litter production, and ability to fix
atmospheric nitrogen combine to make European alder especially desir-
able for planting on spoil banks, which typically contain little organic
matter and available nitrogen.
Establishing European alder on mined sites apparently improves their
suitability for earthworm habitat.
Alder is useful in urban forestry and biomass use of European alder has