Invasives to Watch: Norway Maple

As the weather continues to get nicer, more and more individuals are heading out into the woods for nature hikes, bird watching, or some good ol’fashioned morel hunting.  As you’re walking through the woods you may see Sugar Maples, Elms, Pines, Hemlocks, or so on, but have you thought about the forest and do you know what species are supposed to be there? For instance the Norway maple has made its way into Michigan’s forest and it’s having impacts everywhere.

The Norway maple is originally native to eastern and central Europe, and western Asia, from France all the way to Russia, being a member of the soapberry lychee family, and was commonly used as lumber.  However, in the U.S. it is a popular landscape and street tree throughout many of the states, and is most popular in the East and Midwest.  Its popularity stems from its rapid growth, attractive autumn foliage and wide-site tolerance. 

Being a tree that creates dense shade, it’s starting to have serious impacts on Michigan’s forests.  As it shades out the area below it, it also monopolizes the soil moisture, and reduces overall plant diversity in the immediate site.  It even has the ability to regenerate prolifically under its own canopy.  Even though there is a long lag time before early dispersers mature, when they do, they begin spreading rapidly due to heavy seed production.  It is negatively impacting the Sugar maple and American beech forests by dominating the seedling layer and displacing shade tolerant native species.  This may lead to a reduced woody species diversity, which can have serious impacts on the diets of the wildlife that inhibit Michigan’s forests, such as the white-tailed deer, snowshoe hares, and moose, which commonly browse sugar and red maples for forage. 

Although the Norway maple is shade tolerant and can survive in a variety of soil conditions it generally prefers fertile, moist, well-drained soils, generally being found along roadsides, waste places, hedgerows, thickets, and disturbed and intact forests.

Monitoring road edges and paths is one of the best ways to site and manage the spread of Norway maples.  Because it’s leaves stay green into November it makes identification in the fall a great time to tag and deal with, although identification in the spring, summer and early fall can be done by identifying the milky sap in its leaves and stems.  Removing mature trees that provide the largest source for seed dispersal are the best ones to begin with.  Cutting and girdling are effecting for trees of any size when cut surfaces are treated with herbicide. 

Keeping Michigan’s forest happy and healthy means knowing how to identify the native species from the sneaky invasive ones. By keeping the Norway maple out of the forests, we’re protecting the sugar maples, and all the potential maple syrup we Michiganders take so much pride in making. Protecting the natural habitat and food sources for so many different species is crucial to Michigan’s environment. 

This article is part of the ongoing series on invasive species funded in part with funds from the Michigan Invasive Species Grant Program through the Departments of Natural Resources, Environmental Quality, and Agriculture and Rural Development

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