1. Guides
  2. Invasive Plants of Maryland
  3. Norway maple

Norway maple

Acer platanoides

Description and biology 10

  • Plant: broad deciduous tree up to 90 ft. in height with broadly-rounded crown; bark is smooth at first but becomes black, ridged and furrowed with age; milky sap.
  • Leaves: paired, deciduous, dark green, palmate (like a hand), broader across than from base to tip, marginal teeth with long hair-like tips.
  • Flowers, fruits and seeds: flowers in spring, bright yellow-green; fruits mature during summer into paired winged “samaras” joined broadly at nearly 180° angle; milky sap will ooze from cut veins or petiole.
  • Spreads: to new areas by vegetative reproduction and seed.
  • Look-alikes: other maples including sugar maple (Acer saccharum) and red maple (Acer rubrum). Distinguish Norway by milky white sap, broad leaves, hair-like leaf tips, samara wings straight out, yellow fall foliage.

Ecological threat in the united states 11

Norway maple forms monotypic populations by displacing native trees, shrubs, and herbaceous understory plants. Once established, it creates a canopy of dense shade that prevents regeneration of native seedlings. Although thought to have allelopathic properties (meaning that the plant releases toxins that inhibit or prevent the growth of other plants), research has not been able to confirm this.

Impacts and control 12

More info for the terms: competition, density, fire management, hardwood, natural, presence, shrubs, tree

Impacts: Impacts of Norway maple on communities and ecosystems in North America derive from its apparent competitive superiority, especially on forested sites with a cool, moist, rich, shaded environment (see Site Characteristics). Potential effects of Norway maple invasion include reduced abundance and diversity of native species and alteration of forest community structure.

Norway maple negatively impacts sugar maple/American beech forests of the northeastern United States by dominating the seedling layer and displacing shade tolerant native species [62,64]. In a New Jersey Piedmont mixed hardwood forest, Norway maple seedlings reached densities of 40,500 stems/acre (100,000 stems/ha) or 0.9 stems/ft2 (10 stems/m2) [59]. Norway maple seedlings and saplings appear to be strong understory competitors beneath native species such as sugar maple [31].

Norway maple may outcompete sugar maple for understory dominance in eastern deciduous forests by exhibiting superior growth. In a Pennsylvania mixed hardwood forest from 1987 to 1991, Norway maple saplings displayed an average annual height growth increment that was nearly twice that of nearby sugar maple [25]. Kloeppel and Abrams [25] demonstrated how differences in growth may be attributable to physiological characteristics. When daily mean net photosynthesis on a mass basis was compared for saplings of both species at comparable sites throughout a single growing season, values were consistently higher for Norway maple than for sugar maple. Light response curves revealed Norway maple saplings had significantly (P<0.05) higher maximum photosynthetic rates than those of sugar maple, even though saplings of both species had similar respiration rates and light compensation points. Nitrogen and phosphorus use efficiencies were also significantly (P<0.05) higher in Norway maple than in sugar maple on 2 sampling dates. Norway maple saplings also maintained significantly (P<0.05) higher rates of instantaneous water use efficiency than sugar maple saplings at the same site, indicating greater drought tolerance in Norway maple. In addition, average leaf longevity was 12 days longer for Norway maple compared with sugar maple, which probably also contributed to the apparent competitive differences between the 2 species. While these observations represent a single growing season at a single site, they indicate Norway maple may be able to outcompete sugar maple for understory dominance in eastern forests where sugar maple was previously the dominant late-successional species [25].

Presence of Norway maple in the overstory of northeastern forests may lead to reduced woody species diversity. Norway maple canopy trees appear to be more successful at excluding interspecific woody regeneration than canopy sugar maples [31]. In a New Jersey Piedmont mixed hardwood forest, understory/overstory species relationships were assessed to determine impacts of Norway maple canopy trees on understory species diversity. Although understory species composition was similar beneath Norway maple, sugar maple, and American beech canopies, understory richness was significantly lower beneath Norway maple than beneath sugar maple or beech. Norway maple seedlings comprised 83% of stems and 98% of woody seedlings beneath Norway maple trees [59]. Dense shade provided by Norway maple canopies appears to substantially inhibit woody seedling regeneration, including even Norway maple seedlings [31]. There is concern that Norway maple may alter forest structure by shading out other native understory plant species, such as shrubs and spring ephemeral herbs [55], although data supporting this assertion are lacking.

The impact of invasive Norway maple in forested natural areas is likely to be closely related to seed source proximity [1]. While Norway maple doesn't require edge habitat to successfully establish, its spread into previously uncolonized forest habitats is accelerated where adjacent development with landscape plantings provides a substantial seed source. Conversely, large unfragmented forest tracts may become colonized by Norway maple more slowly [59].

More research is needed to determine the nature and extent of risk posed by Norway maple invasion to native plants, plant communities, and ecosystems throughout North America. For example, Norway maple has been identified as a threat for invading conifer forests of west-central Montana [29].

Control: While removal of overstory Norway maple trees is necessary to end immediate recruitment of Norway maple seedlings, pre-existing Norway maple seedlings and saplings are likely to be abundant and should be removed to enhance growth and survival of native species and to eliminate potential future Norway maple seed sources. Control efforts may require removal of Norway maple trees outside the immediate vicinity of a treatment area due to the influx of seeds from relatively distant sources [61].

Because removal of Norway maple from a site may entail removing a large proportion of existing plant biomass, drastic changes in site conditions and species composition may result. While such efforts will hopefully benefit native species, there is also substantial risk of facilitating invasion by other nonnative plant species. Removal of overstory Norway maple trees in a New Jersey forest dominated by Norway maple and sugar maple resulted in invasion by new or newly conspicuous nonnatives, including tree of heaven (Ailanthus altissima), Japanese barberry (Berberis thunbergii), winged burning bush (Euonymus alata), Japanese honeysuckle (Lonicera japonica), and garlic mustard (Alliaria petiolata) [61].

As of this writing, there is very little information concerning control methods for Norway maple in North America.

Prevention: No information

Integrated management: No information

Physical/mechanical: Research was conducted in a 75- to 80-year old New Jersey forest, dominated in all strata by sugar maples and Norway maples, to determine the effects of a) removal of overstory Norway maples, and b) removal of Norway maple seedlings, on Norway maple and sugar maple seedling banks. Felling or girdling of canopy and subcanopy Norway maple trees significantly (P = 0.003) reduced new recruitment of Norway maple seedlings 2 years after treatment. While sugar maple seedling recruitment did not change significantly (P > 0.05) during this period, overall density of sugar maple seedlings was significantly (P = 0.007) higher. Increased sugar maple seedling density was apparently due to enhanced survivorship of older seedlings, stemming from diminished competition with Norway maple seedlings. In contrast, removal of Norway maple seedlings had no significant (P = 0.12) effect on sugar maple seedling density, and merely resulted in rapid recolonization by newly germinated Norway maple seedlings. Soil disturbance resulting from seedling removal treatments was presumed to enhance germination of Norway maple seeds in the seed bank. It was further speculated that had uprooting of overstory trees been included in the canopy removal treatments, further recruitment of Norway maple seedlings would have occurred [61].

Overstory and subcanopy Norway maple trees that are cut down may resprout from stumps. Larger overstory trees are less likely to produce sprouts that survive for more than a few years, but saplings and subcanopy trees may require further clipping to ensure mortality [61].

Fire: See Fire Management Considerations.

Biological: No information

Chemical: No information Cultural: No information

Taxon biology 13

Acer platanoides, Norway maple, is a medium to large deciduous tree native to northern and central Europe and western Asia (Barnes and Wagner 2004). Its many cultivars are widely planted in North America as a lawn, park, and street tree because they are hardy and cold resistant, tolerate pollution, soil compaction, and other urban conditions, and are relatively free of insect pests and diseases.

The leaves are opposite and palmately lobed with five coarsely toothed lobes; petioles are 8–20 cm long. The tree grows 20–30 m tall with a trunk up to 1.5 m diameter. The yellow to yellow-green flowers, with 5 petals and 5 petal-like sepals, are each 3–4 mm long and occur in corymbs of 15–30 together. The flower clusters, which appear in early spring before leaves have emerged, are larger and more conspicuous than in many North American maples. The fruit, produced in large amounts, is generally a pair of widely diverging samaras (hard nutlets with winged seeds); clusters of three samaras sometimes occur. Maples were classified in their own family, Aceraceae, but are now generally included in Sapindaceae (Stevens 2001)—see Systematics.

In the past 20–30 years, Norway maple has naturalized widely in North America, particularly in urban woodlots and forest edges (Barnes and Wager 2004, Cincotta et al. 2008), and can become dominant in mesic (moist) soils where Acer saccharum (sugar maple) would otherwise grow. Norway maple is classified as invasive in 20 Northeastern U.S. states (USFS 2011) and eastern Canada; it is banned from sale or planting in Massachusetts and New Hampshire. The species is, however, still available at nurseries in other states and continues to be widely planted.

Adverse ecological effects include inhibition of understory growth (including tree saplings) due to its densely shading canopy and its release of allelopathic (defensive) chemicals, so it tends to create bare, muddy run-off conditions immediately under the tree (Galbraith-Kent and Handel 2008; Swearingen et al. 2010). It suffers less herbivory and fewer fungal diseases than sugar maple, which may give it a competitive advantage over sugar maple (Cincotta et al. 2008).

A. platanoides is sometimes confused with A. saccharum (sugar maple) in North America, but they can be distinguished in most characters. Norway maple leaves are usually broader than they are long, while sugar maple leaves are generally longer than wide (or with length=width). Norway maple seeds are flattened and its samara’s wings are widely spread (to 180 degrees); sugar maple seeds are globose, with wings diverging at 45 to 90 degrees. Norway maple terminal buds are large, rounded, and blunt, with only 2–3 pairs of scales; sugar maple has long, sharply pointed buds with many scales. Bark of mature Norway maples has small, often criss-crossing grooves (reminiscent of Fraxinus americana, white ash), while sugar maple bark occurs in broader flat or shaggy plates. Norway maple autumn leaf color is usually yellow to yellow-orange, rather than the brilliant oranges and reds of sugar maple. Finally, Norway maple tends to leaf out earlier in the spring and hold its leaves later in the autumn than sugar maple.

Sources and Credits

  1. (c) Marylise Doctrinal, some rights reserved (CC BY-NC-ND), http://www.flickr.com/photos/30257481@N03/4097992082
  2. (c) Krzysztof Ziarnek, some rights reserved (CC BY-SA), https://upload.wikimedia.org/wikipedia/commons/1/1f/Acer_platanoides_flower_kz.jpg
  3. (c) Krzysztof Ziarnek, some rights reserved (CC BY-SA), https://upload.wikimedia.org/wikipedia/commons/b/b6/Acer_platanoides_fruit_kz.jpg
  4. (c) Huc Marian, some rights reserved (CC BY), https://www.biolib.cz/IMG/GAL/30718.jpg
  5. (c) mmn_noriko, some rights reserved (CC BY-NC), uploaded by mmn_noriko
  6. (c) Katja Schulz, some rights reserved (CC BY), https://www.flickr.com/photos/treegrow/25380296309/
  7. (c) elmaddi, some rights reserved (CC BY-NC)
  8. (c) Kyle Jones, some rights reserved (CC BY-NC), uploaded by Kyle Jones
  9. (c) anonymous, some rights reserved (CC BY-NC), http://www.biopix.com/photos/JOM-Acer-platanoides-(cv-Schwedleri)-00002.jpg
  10. (c) Unknown, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/22733936
  11. (c) Unknown, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/22733935
  12. Public Domain, http://eol.org/data_objects/24640639
  13. (c) Jacqueline Courteau, some rights reserved (CC BY-NC), http://eol.org/data_objects/13612707

More Info

Range Map

(c) Unknown, some rights reserved (CC-BY-SA)

iNat Map

Member of the iNaturalist Network   |   Powered by iNaturalist open source software |   Documentation for developers