Norway Maple

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Norway Maple

Acer platanoides

Name:

Although it is called "Norway" maple, it is actually indigenous to much of eastern Europe and down to the Caucasus. The species Latin name, meaning "like Platanus," indicates the similarity of the leaves to those of Sycamore and Planetree, to which it is not related.

Identification:

Norway Maple is a fast-growing maple which can become 30m (100 feet) tall. It has been widely planted as a street and shade tree due to its vigorous growth and tolerance of poor soil, compaction and pollution.

Norway Maple leaves Norway Maple sap

Photos: John Oyston

At first glance it looks similar to a Sugar Maple (Acer saccharum), but the leaves are usually wider than they are long, and have more lobes than the Sugar Maple. Fortunately there is an easy way to identify the Norway Maple: Break off a leaf and look for the characteristic white sap which comes out of the leaf stalk..

Origin and Introduction:

Norway maple is prevalant in much of Europe from Norway and Sweden to the Caucasus Mountains, Turkey and Iran. It was originally introduced into North America by John Bartram who received seedlings from London in 1756. He went on to sell Norway maples from his nursery in Philadelphia. George Washington ordered two Norway maples from Bartram for his garden at Mount Vernon in 1772.  When Dutch Elm Disease wiped out maples in cities across North America, the Norway maple was often planted as a reliable and rapidly growing replacement, which could withstand city pollution.

The problem:

The Norway maple produces large numbers of seeds, which are typical maple keys, but with the two wings at almost 180 degrees to each other. These seeds mature in September and are spread by the wind. They can germinate even in dense shade, and the seedlings grow quickly.

Maple seedlings in an urban garden

Photo: John Oyston

Norway Maples can out-compete other native trees. They leaf out earlier, and the leaves remain longer into the fall. They tolerate shade themselves, but create deep shade underneath where little else can grow. They suck up water, so that the soil underneath becomes dry. They may also be allelopathic, producing chemicals which prevent native plants germinating. This sets the scene for soil erosion. A typical comment is that the tree looks healthy, but the groiud underneath is a mess and needs work. However, it is almost impossible to grow anything in the shade of a Norway maple. In Toronto backyards some people have given up ad installed plastic turf for their children to play on!

Control Methods:

Smaller seedlings can be removed by hand, and saplings can be dug up. Larger trees may need to be felled by professionals. If girdling or cutting are used the tree must be treated to prevent resprouting. Removing a mature tree to prevent it being a seed source for nearby natural areas is desirable, but can be a major and expensive undertaking. In some cases all that may be possible is to remove some of the lower branches to allow more light through and to reduce seed producition.

Restrictions on Use:

Some US States including New Hampshire and Massachusetts have  banned Norway maples. It is considered invasive in CT, DC, DE, IL, MA, MD, ME, MI, NH, NJ, NY, OR, PA, TN, VA, VT, WI, and WV.

Availability and Alternatives:

Norway Maples are widely sold in nurseries, and many landscapers consider them to be reliable hardy shade trees which they recommend to clients. There are many commercial cultivars, such as the purple-leaved "Crimson King" and a variegated cultivar. Be careful requesting a "Red Maple" as an alternative to a Norway maple, as you may be sold the "Crimson King" version of Norway maple, which has dark red leaves, rather than red maple, Acer rubrum, which has green leaves.

Consider other maples such as red maple (Acer rubrum) - good fall colour , or sugar maple (Acer saccharum) -damaged by road salt. Also consider American basswood (Tilia americana), red oak (Quercus rubra), white ash (Fraxinus americana), tuliptree (Liriodendron tulipifera). In Southern states consider sweet gum (Liquidamber styraciflua), black gum (Nyssa sylvatica), and willow oak (Quercus phellos).

Conclusion:

University of Michigan reports: "The Norway Maple will continue to invade forests across the United States unless the spread is controlled. Because seedlings can survive in deep shade for decades, any attempt to eliminate the Norway Maple would have to be carefully monitored for over 100 years. "

 "If nothing is done regarding the invasion of the Norway Maple we predict that in years to come there will be strong homogenizing of the Maples in forests across the United States. In extreme cases, this would lead to much more plant extinctions, and losses of compatible habitats for animals."