Kingdom : Plantae
Species: A. plantanoides
A species native to Europe, the Norway Maple (Acer platanoides) is a deciduous tree now commonly found throughout the St. Lawrence Lowlands, including McGill University’s Morgan Arboretum. In appearance, the Norway Maple is quite similar to other trees of the genus Acer, including Acer saccharum, the Sugar Maple (7). However, the Norway Maple exhibits various distinguishing traits in terms of its physiology. Norway Maple leaves have between five and seven lobes and are both wider and longer than their Sugar Maple counterparts (8). In addition, Norway Maple buds appear wide and reddish-brown in color as opposed to the pointy, brownish-green buds of Sugar Maples (7). A white sap will also ooze from the petioles of Norway Maple leaves upon breakage (7). Furthermore, these trees will retain their leaves longer than Sugar Maples due to their prolonged growing season, and thus Norway Maple leaves do not transition from green to yellow to brown until after the Sugar Maples have progressed through their red-brown colors (7). In terms of its bark, a Norway Maple trunk is smooth and grey in color at a young age and will develop shallow furrows over time (3).
The species’ natural range is widespread across Europe and West Asia, extending from northern Spain east to the Ural Mountains of Russia, and from southern Scandinavia southwards over the European continent (9). The Norway Maple possesses many desirable traits that contributed to its early popularity and thus its introduction to North America (9). The species maintains a robust growth rate and the ability to thrive in varied soil types (9). In addition, the species is especially tolerant of normally restrictive conditions, including polluted air and soils with high acid or salt content (5).
The aforementioned factors bolstered the success of A. platanoides when it was intentionally introduced to North America in the 1700s for ornamental purposes (10). Farms and towns began cultivating these especially hardy trees for shade, further expediting the invasion of Norway Maples across the Eastern seaboard of the United States (10). Consequently, its current range stretches from Maine down to Tennessee and west to Wisconsin (10). In Canada, the extent of the trees encompasses land from Newfoundland to southern Ontario, as well as the southern portion of British Columbia (4). The species is a prominent inhabitant of the St. Lawrence Lowlands of Quebec; in the 1950s, eight Norway Maples were planted in the Morgan Arboretum, where they continue to thrive in competition against tree species native to the region.
Overall, the presence of Norway Maples is detrimental to native flora and fauna of a given region. This species is prone to growing in dense stands that create excessive shade, thus preventing the growth of native seedlings that require more sunlight (4). An especially shallow root system further hinders the establishment of native trees in a localized area (4). These characteristics allow for the Norway Maples, which have no natural predators in their new North American environment, to outcompete native species, such as the Sugar Maple (4). This dominance displayed by the Norway Maples also impacts native fauna; species including white-tailed deer and moose browse on Sugar and Red Maples, so the loss of these trees to the Norway Maple may threaten animal biodiversity, as well (1).
Various methods have been devised and implemented to control the growth of the highly invasive Norway Maples. Mechanical methods include pruning limbs that bear seeds while leaving the trunk, or girdling larger, more established individuals (6). Girdling is a process in which a ring of cork cambium is cut from the lower trunk, preventing transport of water and nutrients throughout a specimen and killing it over the course of a few growing seasons (6). Nevertheless, girdling alone may not be sufficient; application of tryclopyrs and glyphosphate herbicides may be necessary to expedite the death of the tree (6). Smaller saplings may instead be uprooted directly from the soil with a weed wrench (6). However, the most effective method of control is to avoid planting Norway Maples and to instead plant native varieties that will not negatively impact the environment (6). In 2007, a study was completed that suggested management methods to control invasion. Environment Canada and a team of students promoted manually cutting and applying herbicides to the trees, as well as establishing a buffer zone free of Norway Maples to contain their invasion to a concentrated location (2). The team found that this would help prevent the spread of Norway Maples via wind dispersal of seeds, especially due to the eastward prevailing winds (2).
The invasiveness of Norway Maples can be observed on a small scale in the Morgan Arboretum located at McGill University’s Macdonald Campus. The remaining stumps of the eight originally cultivated trees are located in a concentrated sector of Maple Corner within the Arboretum. The proposed research question is to measure the invasiveness of the Norway Maples from the site of introduction into the surrounding forest. From the origin, transects consisting of 5X5 meter quadrants extend into the forest in the four cardinal directions. Some transects are shorter than others due to natural barriers such as edges between fields and other stands of trees. However, the general method remains consistent; in alternating quadrants along a particular transect, the number of Norway Maple individuals is recorded, along with the trunk diameters of the sizeable specimens. Additional notes, including observations regarding ground cover or the presence of girdling, are also documented. Through this method, it is possible to study the infiltration of Norway Maple trees as they expand from their site of introduction into a forest of Sugar Maples and other species native to the St. Lawrence Lowlands.
1. Abbey T. 2000. Invasive plant information sheet. CT agriculture experiment station [internet]. [cited 2013 Oct 22] 85(1):69. Available from: www.cipwg.uconn.edu/pdfs/norway_maple.pdf
2. Beauregard, F. and C. Idziak. 2008. Norway Maple Invasion in the Morgan Arboretum, Ste.-Anne-de-Bellevue, QC. Report Ecological Monitoring and Assessment Network, Environment Canada p.44
3. Coombes AJDZ. The book of leaves : a leaf-by-leaf guide to six hundred of the world’s great trees. Chicago; London: The University of Chicago Press; 2010
4. Growing better places to live [internet]. 2013 [place of publication unknown]: TreeCanada.ca; [updated 2013 Jul 16; cited 2013 Oct 22]. Available from: http://treecanada.ca/en/resources/tree-killers/plants/norway-maple/
5. Hiwassee River Watershed Coalition, inc [internet]. 2004 [Place of publication unknown]: hrwc.net; [updated 2013 Feb 13; cited 2013 Oct 22]. Available from: http://www.hrwc.net/norwaymaple.htm
6. Love R. [internet]. 2003. Introduced species summary project. [Place of publication unknown]: Conlumbia.edu. [updated 2003 Feb 17; cited 2013 Oct 22]. Available from: http://www.columbia.edu/itc/cerc/danoff-burg/invasion_bio/inv_spp_summ/Acer_platanoides_2.htm
7. More DWJ. Illustrated trees of Britain & Europe. 2013
8. North America, Native Plant Society [internet]. 2001 [Place of publication unknown]: nanps.org; [updated 2013 Oct ; cited 2013 Oct 22]. Available from: http://www.nanps.org/index.php/conservation/alien-invaders/103-joyston
9. Nowak DJ. History and range of Norway maple. Journal of arboriculture 1990;16(11):291
10. Swearinger J. 2010. Plant invaders if mid-Atlantic Natural areas [internet]. Washington (DC): National Park Service; [cited 2013 Oct 22]. Available from: http://www.nps.gov/plants/ALIEN/pubs/midatlantic/acpl.htm