Norway Maple

Acer platanoides

norway maple leaf with tar spot
 Image credit: Leslie J. Mehrhoff

Characteristics

Norway maple, a tree species from the soapberry family, Sapindaceae, is a woody invasive species that can out compete 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 it most cases their offspring loose this trait and end up being green. 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 mixture.

For more information visit WiGl and 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 are when they are saplings or, if they’re mature, before they’re able to produce seeds.

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 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 native tree species like hawthorn (Crataegus sp.) and serviceberry (Amelanchier sp.) that fit better in an understory.

norway maple full tree

(image credit: Leslie J. Mehrhoff) Norway maple full tree image 

norway maple leaves with tar spots

(image credit: Leslie J. Mehrhoff) Norway maple leaves with tar spots 

norway maple flower cluster

(image credit: Robert Vidéki) Norway maple flower clusters 

norway maple seed pods
(image credit: Leslie J. Mehrhoff) Norway maple samaras (seed pods) 

Sources

"Leslie J. Mehrhoff, Robert Vidéki" bugwood.org

"MIPN.org, midwest invasive plant list."

"Norway maple (Acer platanoides)." MISIN, 2020.

"NYIS, Norway Maple"

"Recommended Plant List." NMISN.