Norway maple is a large deciduous tree that grows to 30 m with a broad crown. The leaves grow opposite of each other and consist of 5 sharply pointed lobes versus native sugar maple which has slightly more rounded tips of the leaves. The leaves are also usually darker green and larger than sugar maple, staying greener longer into the fall and leafing out earlier than native maples. The leaf stems exude a milky white sap when broken which is unlike native maples. Clustered flowers emerge in early spring and are light green to yellow. The fruits of Norway maple are a 2-chambered papery winged samara which are pinkish to yellow early in the season and can persist on the tree throughout the winter. The angle between the seed wings is close to 180 degrees and is flatter than sugar maple seeds.
Because generation times are long (30-40 years), Norway maple has spread relatively slowly so far. However, once established, Norway maple is a strong competitor in the forest understory, and can displace native shade-tolerant species such as sugar maple (3) Richness of understory plants is greatly reduced under Norway maple trees compared to native trees, replaced with dense Norway maple seedlings and saplings. (5) Both saplings and mature trees negatively affect the growth of native tree saplings.6 Norway maple also increases nutrient availability and the rate of nutrient cycling in soils (especially on richer soils), which could possibly increase its competitive advantage and also favor some native trees over others. (7) Overall, Norway maple appears to be a slow-moving but significant threat to the canopy and understory composition of mesic forests. (2) Street or yard trees are only problematic because they produce seeds that allow the species to colonize forests.
Manual or Mechanical Control
This page focuses on manual best management practices only. Please contact firstname.lastname@example.org with specific questions on chemical or biological control options.
- Saplings and mature trees may be either cut or girdled, but they usually resprout from the stump. (9) We recommend trying a type of girdling that has been used with success on tree-ofheaven (Ailanthus altissima): In winter or early spring, partially girdle adult trees, by using a drawknife to remove approximately 12” of bark around the whole tree (but not the cambium underneath). This will kill the trees slowly, resulting in fewer stump sprouts. (10) Decrowning (removing all branches from) a mature tree may also have this effect. (11) Kill any sprouts at the end of the growing season, and annually thereafter.
- For small trees, try the “cut and cover” method to prevent stump sprouts: cut several inches above ground level and cover the stump with something that completely blocks light for 1-2 years (e.g., a coffee can, or a heavy-duty black plastic bag zip-tied to the base of the stump). (12)
- Light gaps left by cut or girdled canopy trees may result in rapid growth of Norway maple seedlings or colonization by other invasive species. (9) Monitor these gaps carefully and remove invasive species and/or plant native species to compete.
- Once seed sources are removed, seedlings may either be monitored every few years to remove saplings, or hand-pulled annually until the seed bank is depleted. Soil disturbance from hand-pulling results in an increase in new Norway maple seedling density the following year, (9) but the seed bank is short-lived.
- Prevent or limit seed production by targeting mature trees.
- Prevent saplings from growing to maturity.
- Avoid soil disturbance, which promotes seed germination.
- Munger, G.T. 2003. Acer platanoides. In: Fire Effects Information System. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory. http://www.fs.fed.us/database/feis/plants/tree/acepla/all.html [Accessed 31 October, 2016].
- Bertin, R.I., M.E. Manner, B.F. Larrow, T.W. Cantwell, and E.M. Berstene. 2005. Norway maple (Acer platanoides) and other non-native trees in urban woodlands of central Massachusetts. Journal of the Torrey Botanical Society 132(2):225-235.
- Martin, P.H., and P.L. Marks. 2006. Intact forests provide only weak resistance to a shade-tolerant invasive Norway maple (Acer platanoides L.). Journal of Ecology 94:1070-1079.
- Wangen, S.R., and C.R. Webster. 2006. Potential for multiple lag phases during biotic invasions: Reconstructing an invasion of the exotic tree Acer platanoides. Journal of Applied Ecology 43:258-268.
- Martin, P.H. 1999. Norway maple (Acer platanoides) invasion of a natural forest stand: understory consequence and regeneration pattern. Biological Invasions 1:215-222.
- Galbraith-Kent, S., and S.N. Handel. 2008. Invasive Acer platanoides inhibits native sapling growth in forest understory communities. Journal of Ecology 9:293-302.
- Gómez-Aparicio, L., and C.D. Canham. 2008. Neighborhood models of the effects of invasive tree species on ecosystem processes. Ecological Monographs 78:69-86.
- Webster, C.R., K. Nelson, and S.R. Wangen. 2005. Stand dynamics of an insular population of an invasive tree, Acer platanoides. Forest Ecology and Management 208:85-99.
- Webb, S.L., T.H. Pendergast IV, and M.E. Dwyer. 2001. Response of native and exotic maple seedling banks to removal of the exotic, invasive Norway maple (Acer platanoides). The Journal of the Torrey Botanical Society 128(2):141-149.
- Baran, J. 2010. Field study of technique for combining low-cost, herbicide-free control of woody invasives, in particular Ailanthus altissima, with production of edible mushrooms. Final grant report to Sustainable Agriculture Research & Education (SARE), US Department of Agriculture. http://mysare.sare.org/sare_project/fnc07-670/?page=final&view=print
- Bushell, T. (Westchester Land Trust), pers. comm..
- This method has not been scientifically tested, to our knowledge. A commercial product is available at http://www.buckthornbaggie.com/