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What does it look like?

Common alder (Alnus glutinosa), also known as black alder, European alder or just alder, is a tree that can grow up to c. 15m high. It thrives in wet locations where its association with the bacterium Frankia alni enables it to grow in poor quality soils. The bark of young trees is smooth, glossy and greenish-brown while in older trees it is dark grey and fissured. The branches are smooth and somewhat sticky, being scattered with resinous warts. The buds are purplish-brown and have short stalks. Both male and female catkins form in the autumn and remain dormant during the winter. The leaves are short-stalked, rounded, up to 10cm long with a slightly wedge-shaped base and a wavy, serrated margin. They have a glossy dark green upper surface and paler green underside with rusty-brown hairs in the angles of the veins, and remain green late into autumn.

How is it spread?

  • Rapidly via wind and water

Where is it found?

See the distribution map (when page opens, just click on the green ‘search’ button without changing any of the settings).

Why is it a problem?

  • Thrives in wet locations
  • Fixes nitrogen in the soil, changing the chemistry 
  • Alters the natural environment of stony riverbeds
  • Reduces the habitat available for birds that nest in braided riverbeds
  • Providing cover for predators 

Conservation activities

ECan in collobation with DOC are running a number of local projects to remove alders and willows from wetlands and waterways. See for example the Upper Waitaki Lake Poaka enhancement project.