Western Alder Alnus rubra

Red alder is a deciduous tree in the Betulaceae (birch) family.  It is native to the western coast of North America from Alaska down to California. This is one of the larger alders and grows 65-98 feet tall. It gets its name from the orange/red underbark that was used to make dye by Native Americans.

This tree can be distinguished from other alders by the rolled under margins of the leaves, the stalked buds and impressed veins on the underside of the leaves. Red Alder is able to grow in poor soils due to its association with the soil bacterium, Frankia, which allows it to fix nitrogen. Because of this, they are often used in land reclamation projects. 

This tree grows fairly fast and will spread by seed. It tolerates soils ranging from well-drained gravels and sands to poorly drained clay or organic soils. It will grow in full sun to partial shade and prefers cool wet winters and warm dry summers.

Insects, Diseases, and Other Plant Problems:  Red alder is fairly free from most insect and disease problems, especially when young (age 40 or 50) and uninjured. Phellinus igniarius, a white heart rot, is probably the major cause of cull in older trees. The forest tent caterpillar (Malacosoma disstria), western tent caterpillar (M. californicum), alder woolly sawfly (Eriocampa ovata), striped alder sawfly (Hemichroa crocea), the alder flea beetle (Altica ambiens), and a leaf beetle (Pyrrhalta punctipennis) have caused substantial damage but rarely kill the tree.

VIDEO created by Ryan Contreras for “Landscape Plant Materials I:  Deciduous Hardwoods and Conifers or Landscape Plant Materials II:  Spring Flowering Trees and Shrubs” a plant identification course offered by the Department of Horticulture at Oregon State University