European Alder

Fact SheetAlnus glutinosa

Invader Images

    • European Alder Leaves
      European Alder Leaves
    • European Alder Cones
      European Alder Cones
    • European Alder Infestation
      European Alder Infestation

Common Look-alikes

    • Grey Alder
      Grey Alder
    • Grey Alder leaf
      Grey Alder leaf

Identification

Appearance

Alnus glutinosa is a tree in the birch family that can grow up to 50 ft (15.24 m) tall with the crown spreading from 20-40 ft (6.1-12.2 m) wide. It can be single or multi-stemmed, with a smooth grayish-green bark that turns a speckled grayish-brown.

Foliage

The leaves are simple, alternate and doubly-toothed.

Flowers

The individual flowers are small and inconspicuous individually, but together they form a catkin. They flower in the spring and catkins remain on the trees through the fall.

Fruit

Fruits are obovate samaras. The wings are reduced to narrow thickened ridges.

Biology

This species is considered a watch list species.

Ecological Threat

It is a pioneer and opportunist species that readily colonizes open ground. Its ability to be dispersed by water, and its ability to form monospecific stands, makes it a threat to native wetland species. As a nitrogen-fixing plant, it has the ability to become established on very poor soils.

Origin

It is native across Europe, temperate Asia, and north Africa. It has been planted extensively in North America as an ornamental tree and for erosion control.

Habitat

Although it can tolerate droughts, it prefers moist, damp conditions, especially near water sources. It commonly grows in riparian zones, wetlands, along ponds and lakes. It also grows in forests, forest wetlands and in urban areas.

Life cycle

Alnus glutinosa have the potential to immediately germinate, however, stratification (six weeks) increases germination success. The optimum conditions for A. glutinosa seed germination occur at pH 4 and 25 °C in either light or dark. Once germinated, seedlings are susceptible to low soil oxygen status and drought. Maturity takes 3 - 30 years, depending on ecotype and environment. A. glutinosa is relatively short-lived, with a lifespan of up to 160 years.

Management Options

Mechanical Control

Any time of year when the ground is soft, especially after a rain, hand pull small plants by the base of the stem. Be sure to pull up the entire root system. Hang plant from a branch to prevent re-rooting. For larger plants, use a Weed Wrench™. Continue to monitor the area every year for new seedlings.

Repeated pruning of established plants to ground level without subsequent herbicide application is not effective for European Alder control. Each regrowth results in a thicker stem base and denser branches.

Chemical Control

This method is used for dense populations and best left to a contractor. During the summer months, July to August, spray a 2% glyphosate solution on the entire leaf surface of the plant. In order to avoid drift to native plants, spray only on calm days.

  • Be careful not to damage or kill nearby native plants when conducting management work. And when using herbicides, always follow the instructions on the label.

Citations

Photo Credit

5448630, 5448636, 5448664, Leslie J. Mehrhoff, University of Connecticut, Bugwood.org

5001025, Mary Ellen (Mel) Harte, Bugwood.org

5397664, Robert Vidéki, Doronicum Kft., Bugwood.org

Information Credit 

Bugwood

Invasive Plant Atlas of New England

U.S. Forest Service 

Global invasive species database