Alder

Lore & Background

Alders are deciduous trees and shrubs with alternate, simple, serrated leaves. Their flowers are catkins: elongate male catkins and shorter female catkins on the same plant, often appearing before leaves. Unlike birches, the female catkins are woody and do not disintegrate at maturity, opening like conifer cones to release seeds. The largest species, red alder (A. rubra) on the west coast of North America and black alder (A. glutinosa) native to most of Europe, both exceed 30 meters, while green alder (Alnus alnobetula) is rarely more than 5 meters tall.

The genus is divided into three subgenera: Alnus (trees with stalked shoot buds, catkins produced in autumn and pollinating in late winter or early spring), Clethropsis (trees or shrubs with catkins produced and pollinating in autumn), and Alnobetula (shrubs with unstalked buds, catkins produced in late spring). The oldest fossil pollen identified as Alnus is from northern Bohemia, dating to the late Paleocene, around 58 million years ago. The common name 'alder' derives from Old English 'alor', from Proto-Germanic 'aliso'; the Latin genus name Alnus is the source of French 'aulne' and Spanish 'Alamo' (meaning poplar).

Reader's Guide

Alders hold significant ecological and cultural importance. Ecologically, they are keystone pioneer species, commonly found near streams, rivers, and wetlands, sometimes forming alder carrs. Their most notable trait is a symbiotic relationship with the actinomycete bacterium Frankia alni, which forms root nodules and fixes atmospheric nitrogen, enriching soil fertility. Alders colonize disturbed areas from floods, windstorms, fires, and landslides, and their broad leaves and thin bark make them less flammable than conifers, serving as natural firebreaks.

Their lightweight seeds (1.5 million per kg) disperse easily by wind. Culturally and practically, alder wood has been used for millennia as pilings for piers and wharves, notably in Venice. The bark contains salicin, used traditionally by some Native American cultures to treat poison oak and skin irritations, and by Blackfeet Indians for lymphatic disorders and tuberculosis; recent studies confirm compounds betulin and lupeol effective against tumors.

Alder is used in smoking foods, tanning leather, and making furniture and cabinets. Since the 1950s, Fender Musical Instruments Corporation has used alder for electric guitar bodies, valued for its tight, balanced tone. The inner bark is used in Indigenous smoking mixtures called kinnikinnick. Alder appears in the coat of arms of Grossarl, Austria, and is referenced in the film 'The Tree of Wooden Clogs'.

Did You Know?

• Red alder (Alnus rubra) is the Pacific Northwest's largest alder and the most plentiful and commercially important broad-leaved tree in the coastal Northwest.