Plant of the Month - APRIL 2019

Red Alder (Alnus rubra)

This beautiful deciduous tree of our Northwest Coast early successional forests is in the Birch Family. It is a medium-sized tree with upright trunk, with spreading branches, rarely living beyond 50 years old, and seldom growing bigger than 50 cm diameter and25 metres high. The bark is greenish in younger trees, turning whitish on older, bigger trees. When exposed to the air, the inner bark turns a deep orangey red colour: hence the name, “red alder – Alnus rubra.” The leaves are simple, oval-shaped and pointed, with coarsely toothed edges. The upper surface is bright green, and the lower surface lighter and grayish. The leaves usually remain green until they drop off in the fall, but sometimes they turn a golden yellow. The female flowers are cone-like and borne in small clusters and the male flowers are long, hanging catkins, also clustered; both start to form in the fall, and then mature in the early spring, before the leaves have fully expanded. When the catkins are fully mature, around March, you can see clouds of yellow pollen released in the breeze or if you shake the branches. Once pollinated, the female flowers ripen into small ovoid “cones,” at first bright green and then turning brown and woody. When the fruits are fully ripe the scales open and release numerous small winged seeds that are easily distributed widely by the wind.

Alder has important nitrogen-fixing capabilities. Its roots contain nodules withfilamentous nitrogen-fixing bacteria, enabling alder to replenish nitrogen in the soil, in a way similar to legumes, in a form that makes it available to other plants. This is a great service to the forest, since nitrogen can be limiting, and having alders growing as pioneer trees when forests are cut down or burned, or on roadways and skid trails, can allow the forest to regenerate. As well as providing a nutrient-rich compost for other plants, the alders provide shelter for the young conifers growing up underneath their protective canopy. According to one source, red alders are said to supply as much as 325 kilograms per hectare (290 pounds per acre) to the soil each year. You will often see alders being crowded out by the faster growing conifers, once they have established. It is in no small measure due to red alders that our coastal temperate rainforests are so extensive; the alders create the favourable conditions for the giant conifers!  

As well as serving as a nitrogen-provider and protective species for coniferous trees, alder is also sometimes planted in rotation with Douglas-fir to reduce the incidence of the parasitic laminated root rot (Phellinus weirii) in Douglas-fir forests. It is fast-growing, and can grow from stump sprouts if it is cut. Alder bark, especially the bark of older trees, is often covered with lichens (called corticolous lichens) of various colours, from white to yellow to brownish. Different mosses, and sometimes licorice fern (Polypodium glycyrrhiza), also use alder as a growing substrate. These species create their own mini-ecosystems, with a whole world of associated insects, spiders, mites, millipedes and fungi.

Although some foresters consider this tree a “weed,” and seek to eliminate it by cutting it back or spraying it with weedkiller, red alder is a highly valued species to many. It is a hardwood of excellent quality, used increasingly for furniture and flooring. Coastal First Nations woodworkers use for masks, bowls, spoons and canoe bailers. The wood is also a choice fuel for smoking salmon and other fish, and is commonly cut as firewood. 

Alder bark is also widely used as a dye. Depending on the age of the bark, the amount used, the amount of time it is boiled or soaked in water, and the type of mordant used (formerly urine was a common mordant for alder bark dye), the colour of this dye ranges from bright orangey-red to deep brown or blackish. It is most commonly used to colour cedarbark a reddish tint, contrasting with the natural brown and black-dyed bark in basketry and other products. Alderbark can also be used to dye wool, feathers, and basket sedges.

For the Coast Salish peoples of Vancouver Island, red alder also provided a sweet and nutritious food. To obtain this food, a section of bark is removed from the trunk in the springtime, just at the beginning of the growing season, the sweet, juicy “Inner bark” (cambium and secondary phloem tissue) scraped off, to be eaten fresh as a springtime treat. At just the right time, this layer is thick and gelatinous, and some say it is at its best for harvesting when the tide is high. Bears also enjoy alder cambium and inner bark as a spring food.

Coastal First Peoples also value red alder bark as a medicine, taken as a tea to treat tuberculosis, coughs and stomach problems. A solution of the bark is also used as a wash for skin infections. Alder bark is known to contain antimicrobial compounds, effective against a range of bacteria, both gram-positive and gram-negative. When people harvest alderbark for dye or medicine, they are careful not to girdle the tree, so that it will heal over after awhile. In our coastal forests, one can often see a culturally modified alder tree, with a rectangular piece of bark removed and gradually healing over. 

At Wildwood, red alder is a primary component of our woods, and can be seen in various locations where there are clearings and the ground is moist. Look for it where you see salmonberry (Rubus spectabilis), red elderberry (Sambucus racemosa), skunk-cabbage (Lysichiton americanus) and sword fern (Polystichum munitum).


Klinkenberg, Brian. (Editor) 2017. Red Alder (Alnus rubra). E-Flora BC: Electronic Atlas of the Plants of British Columbia []. Lab for Advanced Spatial Analysis, Department of Geography, University of British Columbia, Vancouver.

Saxena, Geeta, Susan Farmer, R.E. W. Hancock, and G.H.N. Towers. 1995 Antimicrobial compounds from Alnus rubraPharmaceutical Biology33(1):33-36. URL:

Turner, Nancy J. (1998). Plant Technology of British Columbia First Peoples. Victoria: Royal BC Museum.

Turner, Nancy J. and Richard Hebda. (2012). Saanich Ethnobotany: Culturally Important Plants of the WSÁNEC’ People.Royal B.C. Museum, Victoria.