Norway Maple

Characteristics

Norway maple, a tree species from the soapberry family, Sapindaceae, is a woody invasive species that can outcompete other native tree species due to its dense canopy, rapid growth, and prolific seed production.

• reaches 12-18 meters in height and around 30-60 centimeters in diameter
• broad, palmately compound leaves with 5-7 lobes
• large, almost 180° angled samaras produced in late Spring and early Summer
• leaves develop tar spots from exposure to a native fungus known as Rhytisma sp. that also causes the leaves to fall earlier
• shade tolerant and able to thrive under many soil and habitat conditions

Note: Many ornamental varieties of Norway maple exist, including one known as crimson maple, or crimson king maple. These maples have dark red or purple leaves all year long, but in most cases their offspring lose this trait and end up having green leaves. This can make it hard to recognize the spread of this invasive, as the offspring closely resemble native maples. Another way to identify this species is by breaking the petiole as it contains a milky substance.

For more information visit Woody Invasives of the Great Lakes (WIGL) Collaborative and Midwest Invasive Species Information Network (MISIN).

KISMA Management Practices

Norway maple is difficult to remove for its ability to produce large amounts of seedlings and dominate the understory. It was also widely spread by humans as an ornamental in the past before it was categorized as an invasive species, it can still be found in many yards. The best time to remove them is when they are saplings or before they’re able to produce seeds if they are mature.

For Saplings:

1. loosen soil around saplings with a shovel
2. remove saplings using hands or other tools. Make sure to remove as much of the plant and roots as possible
3. dispose of all plant material

For Mature plants, girdling is the most effective strategy. Girdling is the act of cutting deeply into the bark around the trunk, normally in a ring shape, that leads to the death of plant material above the girdled part. 

Native Alternatives

For replacing Norway maple, there are many native species of maple that can be planted instead, such as red maple (Acer rubrum) and sugar maple (Acer saccharum). There are also many native understory tree species like hawthorn (Crataegus spp.) and serviceberry (Amelanchier spp.).