Red Alder

Appearance

Red alder is the largest species of alder in North America and one of the largest in the world, reaching heights of 20 to 30 m . The official tallest red alder stands 32 m tall in Clatsop County, Oregon . The name derives from the bright rusty red color that develops in bruised or scraped bark. The bark is mottled, ashy-gray and smooth, often colonized by white lichen and moss. The leaves are ovate, 7 to 15 centimetres long, with bluntly serrated edges and a distinct point at the end; the leaf margin is revolute, the very edge being curled under, a diagnostic character which distinguishes it from all other alders. The leaves turn yellow in the autumn before falling. The male flowers are dangling reddish catkins 10 to 15 cm long in early spring. Female flowers occur in clusters of 4–6 . Female catkins are erect during anthesis, but otherwise pendant. They develop into small, woody, superficially cone-like oval dry fruit 2 to 3 cm long. 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.

Naming

In moist forest areas ''Alnus rubra'' will rapidly cover a former burn or clearcut, often preventing the establishment of conifers. It is a prolific seed producer, but the small, wind-dispersed seeds require an open area of mineral soil to germinate, and so skid trails and other areas disturbed by logging or fire are ideal seedbeds. Such areas may host several hundred thousand to several million seedlings per hectare in the first year after landscape disturbance .

Distribution

''Alnus rubra'' grows from southeast Alaska south to central coastal California, nearly always within about 200 km of the Pacific coast, except for an extension 600 km inland across Washington and Oregon into northernmost Montana.

Habitat

In southern Alaska, western British Columbia and the northwestern Coast Ranges of the United States, red alder grows on cool and moist slopes; inland and at the southern end of its range it grows mostly along the margins of watercourses and wetlands.To the southeast of its range it is replaced by white alder , which is a tree of similar stature, but which differs in the leaf margins not being rolled under, lack of distinct lobes, and lack of membranous wings on seed margins. In the high mountains it is replaced by the smaller and more shrub-like Sitka alder , and east of the Cascade Mountains by thinleaf alder .Additionally, red alder is often used by scientists as a biomonitoring organism to locate areas prone to ozone pollution, as the leaves react to the presence of high ozone levels by developing red to brown or purple discolorations.