Norway maple (Acer platanoides)

Norway maple leaf

Norway Maple is a small to medium sized deciduous tree in the Maple family. Native to Europe, it was first introduced to North America for cultivation as an ornamental tree in 17561. The Norway Maple and many of its cultivars (such as the Crimson King Maple) have become popular choices for urban tree plantings due to their rapid growth and high tolerance of urban stressors. As a result, it can now be found all across Canada and the United States in and around urban centers. Norway maple is commonly found throughout the Credit River watershed.

Norway Maple has simple leaves with an opposite arrangement and 5 to 7 lobes. The leaves are dark green and typically wider than long. Norway Maple leaves contain a milky white sap that exudes from the stem when picked. The milky white sap can be used to easily distinguish it from other maple species.


Norway Maple milky sap

Norway Maple seeds 

When mature, the tree can reach heights of 40 – 60 feet, with a rounded appearance, due to the formation of the foliage into a dense crown2. The flowers are yellowish green in colour and appear in stalked clusters from mid to late April. The fruit is a double samara (maple key) with wings at a nearly perfect horizontal (180 degree) angle. Norway Maple has the ability to produce a large quantity of seeds, as well as produce seeds earlier than many other maple species. Their seeds mature in September and are dispersed by wind.

Norway Maple can be mistaken for the native Sugar Maple, however Sugar Maple leaves contain five lobes and are longer than wide. The Sugar Maple leaf sap is clear and the leaf buds have a sharp point, compare to the round leaf buds of Norway Maple.


Norway Maple leaf


Sugar Maple leaf

Norway Maple usually invades natural areas in and around cities due to their use in landscaping. Once established, Norway Maple forms a dense forest canopy that shades out most other species. The seedlings (which are highly shade tolerant) can form a thick mat on the forest floor that will further limit regeneration of other native trees and shrubs1. Because few species can grow in the shade of a Norway Maple, forest floor vegetation becomes increasingly scarce, causing the exposure of bare soil and increased erosion3.

The best strategy to control the spread of Norway Maple is to prevent planting them altogether. However, once established, young trees can be removed by hand pulling or weed wrenching. For larger trees, girding the trunk can be an effective management technique. Trees are best pulled when they are young, due to their ability to establish themselves quickly within an environment, after which they become too large to remove by hand. Chemical control is an effective technique for mature trees.

For more information on Norway Maple, please contact CVC via email or to report sightings of Norway Maple call the Ontario Federation for Anglers and Hunters Invasive Species Hotline at 1-800-563-7711 and add the sighting to the EDDMaps Ontario website.

References:

  1. Webb, S. L., and Wycoff, P.H. 1996. “Understory Influence of the Invasive Norway Maple (Acer platanoides)”. Bulletin of the Terry Botanical Club 123: 197-205.
  2. Abbey, T. Connecticut Invasive Plant Working Group. 2000. “Invasive Plant Information Sheet: Norway Maple (Acer platanoides). Connecticut Invasive Plant Working Group. Web. 16 August 2018. http://www.hort.uconn.edu/cipwg/pdfs/norway_Maple.pdf
  3. Griggs, J.A., Wanger, S.R., and Webster, C.R. 2005. “Spatial Characteristics of the Invasion of Acer platanoides on a Temperate Forested Island”. Biological Invasions 8: 1001 – 1012.
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