Bigleaf Maple

Bigleaf maple (Acer macrophyllum, Sapindaceae) is a fast-growing native deciduous tree ranging from southwest British Columbia to southern California, from sea level to 1,650 meters. It is the largest-leaved of all maples, with opposite, simple leaves 20 to 30 centimeters across bearing 3 to 5 toothed lobes; the petiole yields milky sap when detached. The tree reaches 60 feet typically (up to 100 feet) with a spread of 39 feet. Small fragrant greenish-yellow flowers hang in drooping clusters (10 to 15 centimeters) in April to May, followed by large pubescent double samaras. Fall color is yellow to gold.

Bigleaf maple grows in sun to part shade on adaptable soils (pH 4.8 to 7.2) with moderate water needs and low drought tolerance, hardy in Zones 5b to 8b. Growth is fast, reaching about 30 feet at 20 years, with a moderate lifespan. It resprouts vigorously from stumps. Disease pressure is notable, with 19 documented associations including anthracnose, bigleaf maple decline, sooty bark disease, tar spots, and Verticillium wilt. Pest associations (15 documented) include carpenterworm, cottony maple scale, maple bladdergall mite, and maple tip moth. A fastigiate cultivar (40 feet) has been selected for street tree use.

The dominant native hardwood in our lowland forests. Bigleaf maple tolerates the full range of Puget Sound conditions: glacial till, alluvial clay, seasonal flooding, summer drought, and deep shade. The moss-draped trunks are a signature of our regional landscape. The disease to watch is bigleaf maple decline, which has been killing trees across the region since the mid-2010s. Researchers have not identified a single causal agent, but drought stress appears to be a contributing factor. Anthracnose hits hard in cool, wet springs but is cosmetic and the tree recovers. Tent caterpillar defoliations look alarming but rarely cause lasting damage to healthy trees. If you cut one down, expect aggressive stump sprouting; a single stump can push three meters of growth in one season.

— Chris Welch, ISA Certified Arborist