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Red alder (Alnus rubra, Betulaceae) is an important forest tree of western North America. It is the world's largest species of alder, reaching heights of 20-35m. The official tallest red alder (1979) stands 32 meters tall in Clatsop County, Oregon, USA.

Red alder has oval leaves with bluntly serrated edges and a distinct point at the end. The leaves turn yellow in the autumn before falling. The bark is mottled ashy gray and smooth, often draped with moss; red alder is named for the bright rusty red color that develops in bruised or scraped bark. A russet dye can be made from a decoction of the bark, and was used by native Americans to dye fishing nets so as to make them less visible underwater. Male alder flowers are dangling reddish catkins, and female flowers are erect catkins which develop into small woody cone-like strobiles. Alder seeds develop between the woody bracts of these strobiles and are shed beginning in the late summer and continuing through the winter. Alders (genus Alnus) can be distinguished from their birch cousins (genus Betula) by the strobiles: alder strobiles are tough and hold together until decay takes its toll after two or three years, while birch strobiles self-destruct soon after ripening.

In the northwestern Coast Ranges of the USA red alder grows on cool and moist slopes; inland and at the southern end of it range (California) it grows mostly along streams and in swamps. It is associated with Douglas fir (Pseudotsuga menziesii), western hemlock (Tsuga heterophylla), grand fir (Abies grandis), western redcedar (Thuja plicata), and Sitka spruce (Picea sitchensis) forests. Along streambanks it is commonly associated with willow, red osier dogwoodCornus ''Benthamidia ''Swida Dogwoods are one to three genera (depending on botanical interpretation) of deciduous shrubs and trees in the family Cornaceae. Sub)genus Cornus Cornels 4 species) Cornus chinensis (Chinese cornel). Cornus mas (European Cornel (Cornus stolonifera), Oregon ash (Fraxinus latifolia) and bigleaf maple ( AcerAcer can refer to one of the following: For the company named Acer see Acer (company). For the tree of the Acer genus, see Maple. macrophylum). In the high mountains it is replaced by the smaller Sitka alder (Alnus sinuata), and east of the Cascade Mountains by thinleaf alder (Alnus tenuifolia).

In moist forest areas red alder will rapidly cover a former burn or clearcut, temporarily preventing the growth of conifers. Alders are prolific seed producers but the 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 (Zavitkovski, J.; Stevens, R. D.; 1972, "Primary productivity of red alder ecosystems", Ecology 53(2): 235-242). This vigorous growth has earned it the designation of a "trash tree" by the timber industry. Herbicide spraying of red alder over large areas of coastal OregonOregon is a state located in the western United States bordering the Pacific Ocean, California, Washington, Idaho, and Nevada. Its northern border lies along the Columbia River and the east along the Snake River. Two north-south mountain ranges the Coasta and WashingtonWashington is a state in the Pacific Northwest of the United States. It should not be confused with Washington, DC, the nation's capital. To avoid confusion, the state is often called Washington state . Although the state capital is Olympia, the largest c has resulted in a number of lawsuits claiming it caused health problems, including birth defectA birth defect is a physical or mental abnormality present at the time a child is born. Birth defects range from minimal, such as birthmarks, and slightly mobility-impairing, such as amelia of the legs, to very serious, such as cerebral palsy, and incompas and other side effects.

The wood is not durable in outdoor use but due to its workability and ease of finishing it is increasingly in use for furniture and cabinetry. Historically it has not been considered of high value for timberTimber is a term used to describe clusters of trees. It is also used to describe wood throughout its processing from the time it is cut down to the time it is used as a structural material. The word timber is also used as an exclamation when a tree falls. but alder is becoming one of the western USA's more important hardwoods. The Fender guitar company chose red alder to use in the body of its original Stratocaster® model electric guitar, and it has remained a popular choice for guitars although alder seldom exhibits the spectacular curly or quilted grain seen in some of the maple lumber used in instruments. Alder wood ranges from white through pinkish to light brown, is relatively soft, and has medium luster and chatoyance. It is easily worked, glues well, and takes a good finish.

Twigs and buds of alder are only fair browse for wildlife, though deer and elk do browse the twigs in fall and twigs and buds in the winter and spring. Beaver eat the bark. Redpolls, siskins, and finches eat alder seeds, as do deer mice.

Red alder is also very valuable for playing host to the nitrogen fixing actinomycete Frankia . It is this ability which allows alder to grow in nitrate-poor soils. Its rapid growth makes it useful in covering disturbed land, such as mine spoils. Alder leaves, shed in the fall, decay readily to form a nitrogen-enriched humus. And it is being considered as a rotation crop to discourage the root pathogen, Phellinus weirii (Laminated root rot).

Red alders are not commonly planted as ornamentals but will do well in wet swales or on stream banks. If used domestically they should be planted well away from drainpipes, sewage pipes, and water lines, as the roots may well invade and clog the lines.