Black (European) alder

(Alnus glutinosa)

General description:

A fast-growing, multi-stemmed tree in the birch family. Trees roots have nitrogen-fixing microbial symbionts. New leaf-growth is sticky to the touch.

Ecological threat:

  • Invades all habitat types: floodplain forests, forest edges, prairies, wetlands, grasslands, streamsides, bogs and fens, marshes, lakeshores.
  • Widely planted since colonial times and naturalized.
  • Prefers wet soils and full sun, can be tolerant of dry conditions and shade.
  • Trees can produce hundreds of thousands of seeds each year.
  • Readily hybridizes with other alder species, threatening native populations.
  • Seeds are dispersed mainly by water; seeds can float for over a year.
  • Black alder increases invasive earthworm (Lumbricus terrestris) activity.
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