Red Alder Alnus rubra

If you forage mushrooms west of the Cascades, you already know red alder. It is the most common hardwood in the Pacific Northwest and the largest alder species in North America, reaching 50 to 90 feet tall in lowland forests, along streams, and on disturbed ground from coastal Alaska to central California. For mushroom hunters, what makes red alder matter is what it does to the soil and what happens to it after it dies.

Red alder fixes atmospheric nitrogen through a symbiotic partnership with Frankia bacteria in its root nodules. This enriches the surrounding soil, boosting fertility for the entire plant and fungal community. When alder trees die and fall, those nutrient-rich logs become prime substrate for saprotrophic fungi — especially oyster mushrooms, which fruit on dead alder more reliably than on almost any other PNW hardwood.

Red alder is a pioneer species. It is the first tree to colonize landslides, clearcuts, stream banks, and other disturbed sites. The smooth gray bark is thin and develops a characteristic mottled appearance as white lichens colonize it with age. Older trees show slight fissuring but never develop the thick, deeply ridged bark of conifers. Leaves are oval, serrated, 3 to 6 inches long, bright green above and paler below. Small woody cones persist in clusters on the branches through winter, making identification easy year-round.

Most red alder grows below 2,500 feet elevation in moist lowland forests and riparian corridors. It is a relatively short-lived tree — 60 to 100 years — which means dead and dying alder is constantly available as mushroom substrate throughout west-side forests. The wood is valued for furniture, cabinetry, and smoking food, where it produces the mild alder smoke flavor that defines PNW smoked salmon.

Associated Mushrooms

Red alder supports a rich community of saprotrophic fungi. Dead and dying alder wood is among the most productive hardwood substrate in the PNW, hosting oyster mushrooms, bracket fungi, and late-season decomposers. Here are some of the most notable associations.

Oyster Mushroom

Pleurotus ostreatus

One of the most common saprobic mushrooms on dead alder. Alder logs are a classic oyster mushroom substrate — if you find a downed alder in wet weather, check it for oysters.

Saprotrophic Edible Photo: Jeremy Collison

Deer Mushroom

Pluteus cervinus group

Common on decaying alder logs and stumps. A reliable indicator of well-rotted hardwood. Pink spore print and free gills distinguish it from look-alikes.

Saprotrophic Caution Photo: Jeremy Collison

Artist’s Bracket

Ganoderma applanatum

Perennial bracket fungus that may be found on dead and dying alder. Brown woody shelves persist for years, adding a new pore layer each season. The white pore surface bruises brown.

Saprotrophic Photo: Jeremy Collison

Late Fall Oyster

Sarcomyxa serotina

Fruits late fall through winter on hardwood logs including alder. Distinctive olive-green to yellow-brown caps with a gelatinous texture separate it from true oysters.

Saprotrophic Edible

Honey Mushroom

Armillaria ostoyae

Both parasitic on living alder and saprobic on dead wood. Fruits in large fall clusters at the base of trees. Must be thoroughly cooked — never eat raw.

Parasitic Saprotrophic Caution Photo: Sharon Squazzo / CC BY