European Alder

Common name: European alder
Scientific name: Alnus glutinosa (L.) Gaertn.
Synonyms: European black alder, common alder, alder

Legal Status: Restricted

Propagation and sale of this plant are prohibited in Minnesota. Transportation is only allowed when in compliance with Minnesota Statute 18.82. Although Restricted Noxious Weeds are not required to be controlled or eradicated by law, landowners are strongly encouraged to manage these invasive plants on their properties in order to reduce spread into new areas. Minnesota Noxious Weed Law.

Life cycle: Perennial
Related species: Alnus incana, Alnus serrulata, Alnus viridis (all native to North America)
Habitat: Grows in full sun to partial shade, adaptable to a wide range of environmental conditions but prefers moist to wet soils that are rich and deep.
Impact: Environmental, rapid growth, highly adaptable (can fix nitrogen from the air to colonize poor soils and change chemical composition of the soil), prevents growth of understory shrubs and other plants.
Native range: Europe, northern Africa, and western Asia

Background

European alder was brought to the East Coast of the United States from Europe by early colonists. Since its introduction, it has escaped cultivation and naturalized in the mid-western and northeastern United States. It is grown as a shade tree in urban areas, and near wet areas which can provide erosion control.

Identification

European alder is a monoecious deciduous tree that can grow up to 60-70 feet tall. The leaves are smooth, 3-5 inches long, and have a serrated margin. The male flowers are long and drooping catkins, while the female flowers are smaller and round catkins. The female catkins develop into brown, cone-like structures that can float on water as a means of seed dispersal. The bark is grayish brown with warty, horizontal strips, and shallow cracks.

Management

• Mechanical: Pulling small seedlings, cutting (in conjunction with herbicide treatment to the stump) for adult trees, or girdling (in conjunction with herbicide treatment)
• Chemical: Foliar spray, cut stump, and basal bark herbicide treatment
• European alder does not start producing seeds until its third year, so older plants should be removed first to prevent seed spread.
• If removing the tree is not an immediate option, the branches can be removed to prevent seed spread if they have not gone to seed yet.

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