Red Alder

Red alder is the pioneer of disturbed soils and early succession, a fast-growing deciduous tree that instantly colonizes recently logged or cleared land. The smooth, light gray bark is often nearly white due to lichen growth, creating a striking contrast with the red inner bark exposed at branch scars. The leaves are oval, doubly toothed, and often sticky when young. Male catkins are long and drooping; the female catkins harden into small, woody, cone-like structures that persist through winter and release tiny winged seeds. Native from Alaska to central California, the tree reaches 60 to 90 feet and forms dense pure stands in wet areas.

Red alder is nitrogen-fixing, enriching depleted soils and improving site conditions for subsequent species. This rapid growth makes it valuable for short-term screening, watershed restoration, and wildlife habitat, though its short lifespan (60 to 80 years) means planning succession is essential. The tree demands moist, well-drained soils and performs poorly in dry sites. It is highly susceptible to trunk diseases, particularly bleeding canker and Armillaria root rot, which accelerate decline in older trees. Multiple insects attack it, including alder leafminers and flea beetles. Plant red alder with the understanding that it is a temporary element in the landscape: valuable for rapid establishment of structure and nitrogen enrichment, but plan to remove or manage decline within 40 to 60 years.

Red alder is the pioneer species that defines Puget Sound disturbance ecology. Cut a forest, grade a slope, abandon a field, and red alder is the first tree on site. It fixes atmospheric nitrogen through Frankia root symbiosis, building soil fertility for the conifers that will eventually replace it. Growth is explosive (50 feet in 20 years) but lifespan is short (50-70 years). The wood is soft and breaks in ice storms. In managed landscapes, the main decision is whether to fight it or work with it. On saturated sites with poor drainage where little else will establish, red alder is a legitimate choice for fast canopy. Drippy dieback is the most visible disease, causing blackened branch tips in spring. Tent caterpillars defoliate alders regularly but healthy trees refoliate within weeks.

— Chris Welch, ISA Certified Arborist