Red Alder

Alnus rubra

Red Alder, Pacific Coast Alder, Oregon Alder, Western Alder
Alnus rubra   (AL-nus ROO-brah)
Birch family–Betulaceae

Red Alder is a native deciduous broadleaf tree with elliptical leaves whose margins roll under with coarse blunt teeth. Its trunk is straight with thin, smooth, ash gray to gray brown bark, covered with white patches of lichen–which gives the appearance of Birch. Its branches are slender and form a pyramidal crown. Playing an important role as a fast growing pioneer species, they build up the soil with their copious litter, and enrich it with nitrogen compounds formed by symbiotic bacteria that live in root nodules. They improve soil fertility by fixing atmospheric nitrogen in a form that can be used by other plants. They may live 40-100 years of age and grow 40-100 feet tall.

Structure: Straight trunk up to 18” in diameter. Bark is thin and gray with smooth white patches of lichens. The inner bark is reddish brown. Fresh wood turns deep red. Fast-growing, 1 meter per year until 20 years of age. Survives disturbance by re-sprouting. Wood is diffuse, porous, moderately light and soft. 

Leaves: Alternate, simple, broadly elliptic and sharply pointed at the base and tip. Texture is smooth above, glabrous and slightly rust-colored below, gland-dotted with fine soft hairs. Leaf margins are wavy, roll under with coarse, blunt teeth. Leaves remain green until dropping in the fall.

Flowers: Monoecious. Male flowers (catkins) appear as hanging, tassel-like cylindrical spikes in clusters of two to four. They are reddish-orange with yellow highlights and emerge before or with leaves. Female flowers are borne in small stubby cones and appear green when young turning brown.

Fruits: Clusters of small-scaled brown cones (fruit) containing oval-shaped membranous winged seeds or nutlets, remain on the tree over winter. Each cone contains from 50 to 100 seeds. Abundant seeds are wind dispersed from May to winter.

Distribution of Red Alder, U.S. Dept. of Agriculture

Habitat: Full sun for seed germination; clay, deep sandy loam and nutrient poor soils; low elevation; moist to wet sites. Red Alder trees invade clearings or burned-over areas and form temporary forests enriching nutrient poor soils with nitrogen while depleting phosphorus levels. Soil levels are built up with their copious litter, and enrich it with nitrogen compounds formed by symbiotic bacteria that live in nodules on their roots. Actinomycetes (filamentous bacteria) in the genus Frankia invade Alders through their root hairs and stimulate cell division, forming nodules on the roots. Species of Frankia remove nitrogen from the air and ‘fix’ it in a form useful to plants. Red Alder stands are eventually succeeded by Douglas fir, western hemlock, and sitka spruce which do not rely on phosphorus but do need high nitrogen levels.

Wildlife Use: Red Alder enhances soil nutrients which encourages a thick understory of plants to support diverse wildlife. It supplies food, shelter, climate modulation and nutrients for a variety of mammals, birds, amphibians, insects, bacteria and plants including lichen, fungi and algae. Bark, leaves, twigs, buds and seeds are used by various animals. Most of the seeds remain on the tree well into the fall and winter months, providing valuable resources for seed-eating animals when other foods are scarce. Nesting and roosting birds find shelter in the tree canopy as well as insects. The cool air produced by shade and transpiration is sought after by black tailed deer and other wildlife including fish.

Mammals that feed on the leaves, twigs, and buds are deer, elk, snowshoe hares and porcupines. Beavers feed on the bark and use stems to build dams and lodges. Mice feed on seeds. Livestock browse the young saplings and leaves.

Birds that feed on seeds are redpolls, siskins, goldfinches, mallards, widgeons, grouse, bushtits, kinglets, vireos, warblers, and chickadees. Alder also provides valuable nesting and roosting.

Western Tiger Swallowtail Photo: ©JL Cummins

Insects rely on the Alder catkins which are one of the first pollens for honey bees, butterflies and moths. Swallowtail butterfly larvae feed on the leaves.

Soil organisms feed on the organic debris and nutrients from Alder leaves and roots.

Fish rely on the shade, soil stability and insect food created by healthy riparian habitat.

Native American Use: Red Alder was sourced for many uses; food preparation, medicine, dyes, smoking and fabrication. Food: The inner bark was often dried, grounded into a powder and then used as a thickener in soups or mixed with cereals when making bread. Alder wood was used for smoking foods. Medicine: Infusions of the bark which contains salicin, a chemical similar to aspirin, were used to treat various illnesses; anemia, colds, congestion,  pain, headaches, rheumatic pains, internal injuries, diarrhea, laxative and to regulate menstruation. The Salinan used an extract of the bark to treat cholera, stomach cramps, and stomachaches. Boiling the bark in water made a wash to treat skin irritations and sores. Poultices were applied to reduce swelling, eczema, sores, and aches. Chewing the bark helped to heal sores and ulcers in the mouth. The twigs were made into infusions that served as liniments for sprains and backaches. Dyes: Various layers of the bark yield red, red-brown, brown, orange, and yellow dyes to color baskets, hides, moccasins, quills, hair, basket decorations and fishnets. Fabrication: A mixture of red alder sap and charcoal was used by the Cree and Woodland tribes for sealing seams in canoes and as a softener for bending boards for toboggans. Large tree trunks were hallowed out for canoes while smaller pieces used for food dishes, furniture, sashes, doors, millwork. Roots were used in baskets made by the Hua, Whilkut, Nongatl, Lassik, Wailaki, Yurok Wiyot, and Pomo tribes.

Current Use: Red Alder wood is a high quality hardwood with a fine, even textured, that is important commercially in the Pacific Northwest. It is used for cabinetry and furniture making as well as a variety of other purposes including plywood, veneers, paneling, pulp, and firewood.  Close grain structure of wood, softness and reluctance to shrinkage and swelling make it ideal for electric guitars.

USDA Plant Database 
Washington Native Plant Society Website
Wildflowers of the Pacific Northwest
Native Plants PNW
Lady Bird Johnson Wildflower Center
OSU Extension-Pacific NW Native Plants by Plant Community