Red alder

Alnus rubra, or red alder, is a deciduous broadleaf tree native to western North America. It is the largest species of alder in North America and one of the largest in the world. It can get to heights of 20 to 30 meters.

The male flowers are dangling reddish catkins, while female flowers occur in clusters of 4 to 6 (8). They develop into small, woody, cone-like oval dry fruit.

The seeds develop between the woody bracts of the 'cones' and are shed in late autumn and winter. Red alder seeds have a membranous winged margin that allows long-distance dispersal. The species can live up to 60 years before being seriously afflicted by heart rot.

The name "red alder" comes from the bright rusty red color in bruised or scraped bark. It grows from Southeast Alaska to central coastal California, mostly within about 200 kilometers of the Pacific coast. In moist forest areas, it covers former burns or clearcuts, often preventing the establishment of conifers.

The tree hosts the nitrogen-fixing actinomycete Frankia in nodules on roots. This helps if grow in nitrogen-poor soils and so makes it an important early colonizer of disturbed forests and river areas. Alder leaves, shed in the fall, decay readily to form a nitrogen-enriched humus.