Acer platanoides – A Cautionary Tale

By Merle Gunby, Owen Sound

(Note: This article first appeared in The Hart’s Tongue Herald, the newsletter of the Owen Sound Field Naturalists. It is reproduced here with the permission of the author).

Leaves: opposite, simple, dark green above,lustrous below; petiole exudes milky sap when   broken.

Habit: rounded, symmetrical crown, usually with very dense foliage and shallow root system. Flowers: yellow, produced in erect corymbs (clusters).

Fruit: samera (winged). Wings of the “keys” are widely spread.

Landscape value: over used and over rated. Native Habitat: continental Europe.

Cultivars: many.

This abridged listing from a tree nursery manual describes the Norway maple, Acer platanoides, a tree that has dominated urban landscape plantings for many years. However, a contrarian might include additional, diagnostic terms, for example: Leaves: leathery, cling to the tree in autumn, tend to smother other plants and grass when they do fall. Habit: casts dense shade, shallow-rooted — making it difficult for even grass to grow under it, needs lots of space. Fruit: over abundance. The “keys” create a nuisance when they drop, clogging drains and starting new generations where they are not wanted. Cultivars: many, the most well-known being Crimson King. Note: subsequent generations of cultivars tend to regain characteristics of the parent Species.

A public official recently enthused, referring to red foliaged Norway maple cultivars: “I just love all those Red Maples growing in our city … they’re so beautiful!” — Well maybe, however the real red maple, Acer rubrum is a species indigenous to the Grey Bruce area. In some locations it could be an alternative to the Norway maple.

So far these critical comments are a matter of individual aesthetic taste and perhaps none of our business. But, it looks as if we’re doing it again – introducing an exotic species that having escaped the restrictions present in its original ecology, thrives in the new environment, making a comfortable home for itself, crowding out native flora thereby disrupting the natural biological cycle. In the example of Norway maple this becomes a major public concern when seedlings start appearing in neighbouring woodlands.

A cursory Google search informs us that many American states have restricted or banned the use of Norway maples. Some are even uprooting them from forested areas because their fecundity and dense shade inhibits native trees and herbaceous plants from regenerating. A quote from a Google page illustrates the problem in some of Toronto’s parks.

“The leaves of the sugar maple, Acer saccharum, had fallen; those of the Norway maple were still retained. As a result it was all too apparent just what a threat this species presents to the forested ravines and other natural remnants of the maple-beech and oak forests of Toronto… A stunning and horrifying image was seen in  many of Toronto’s forests, of partial to continuous understory of bright yellow [Norway maple] foliage.”

One individual’s effective but drastic solution occurred when he purchased a home with a well established Norway maple in the front yard. His first landscape chore was to climb the tree with a chain saw in hand, removing the tree limb by limb. Even the root was dug out.

He now has a nice lawn. And that is a whole other tale.

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