Species Highlight: Bigleaf Maple
Visitors to Oregon are awed by the enormous leaves of our Oregon maple Acer macrophyllum. The tree is native to the Pacific Northwest and is commonly called the bigleaf maple due to the huge size of its deciduous leaves. The bigleaf maple boasts the largest leaves of any maple tree, with its 5 lobes stretching up to 12 inches across.
Bigleaf Maple Growth Habit
In thick stands, the tree grows up to 100 feet tall in a columnar shape. In the open, growth is slightly shorter with a more rounded canopy 75 feet across. Their height, canopy spread, and large leaves make them ideal shade trees. The bigleaf maple above, left, shades the roof of a house in southwest Portland. The density of shade cast by the huge leaves can be seen under the canopy of the bigleaf maple above, right. Bigleaf maples grow very quickly when young, but slow their growth rate with age. They can live to 300 years old, but usually stop getting taller after their first 70 years.
Yellow flowers grow in drooping 6 inch clusters in the spring before the emergence of bright green leaves.
The flowers of spring are followed in the summer by bunches of large, fuzzy “helicopter” seeds, or winged samaras, which develop throughout the season and are dispersed by the wind after fully ripening in the fall. The leaves turn a brilliant yellow in the fall before the large leaves drop to form a dense carpet of brown leaves. Bigleaf maple bark is grey and deeply ridged.
Bigleaf Maple Ecosystem
In their natural habitat, bigleaf maples are found most commonly in the forest or on forested slopes. They are also found less commonly growing on higher ground in riparian habitat near water. Because the bark of the bigleaf maple is deeply ridged, it plays host to many epiphytes, which do not need soil to grow. Mosses and a licorice fern can be seen growing on the bark of the bigleaf maple above. The bigleaf maple feeds many small mammals (like the Douglas squirrel) and birds on its seeds and flowers.
Bigleaf Maple Planting and Care
Bigleaf maples grow best on deep, well-drained soil in full to part sun. These stunning trees have a shallow, spreading root system, and can tolerate seasonally wet soil for short periods of time. If you have a large yard with these conditions, be sure to plant the tree far enough away from any structures to allow the canopy to reach its full spread of 75 feet. As they make great shade trees, planting the tree to the southwest of your home or gathering area will maximize its shade potential in the summer.
Summer supplemental watering will allow the leaves of the tree to reach their full size. When the leaves fall in autumn, the thick blanket of leaves should be raked off turf to prevent the turf from dying.
Our arborists generally recommend pruning bigleaf maples about every five years to encourage a robust, balanced form. Structural pruning involves the selective removal of crossing or rubbing branches, removal of deadwood, and slight thinning for removal of flawed or suppressed growth. Bigleaf maples’ spreading canopies will often grow out and down. If they are growing close to buildings and roadways, regular clearance pruning may be necessary to raise the canopy for increased clearance.