Thinleaf Alder

You spot thinleaf alder as a thicket-forming shrub or small tree along streams in western mountains from Alaska to New Mexico, where its thin, smooth green-gray or reddish-brown bark and multiple stems signal its colonizing habit. Its leaves are significantly thinner than those of white alder, with more finely toothed margins and a dull green color. This mountain alder rarely exceeds 40 feet in height and often remains shrubby, especially on harsh, exposed sites.

Thinleaf alder tolerates cold, harsh mountain sites with short growing seasons and precipitation from 10-20 inches at its dry end to much higher in the Cascades. In western Washington mountains, it establishes readily on wet disturbed soils and eroding streambanks where its nitrogen-fixing roots stabilize soils and begin enrichment. It is fast-growing (20 feet in 20 years on good sites) and moderate-lived; watch for similar diseases as other alders. This species is primarily valuable for riparian and avalanche path restoration in mountain settings.