Norway maple is a nonnative tree, usually 40 to 98 feet (12-30 m) in height, with widely spreading, ascending branches [10,18,29,52]. In Europe, Norway maple trees typically grow to a maximum diameter at breast height of 76 inches (190 cm) and live to 150 years [41]. Bark on older trees becomes furrowed [48,52]. Fruits of Norway maple are 2-winged samaras and each half of the fruit is typically 1.4 to 2.2 inches (3.5-5.5 cm) long [48,52,57].
The preceding description provides characteristics of Norway maple that may be relevant to fire ecology and is not meant to be used for identification. Keys for identifying Norway maple are available in various floras (e.g. [18,34,45,48,52,57,63]). Photos and descriptions of Norway maple are also available online at Plants Database, Michigan State University Extension, and Oregon State University websites.
The biology and ecology of Norway maple are not well-studied in North America. More research is needed to better understand its key biological traits, habitat requirements and limitations, and interactions with native North American flora and fauna.
Norway maple is native to continental Europe and western Asia. It was introduced to the United States in the mid- to late 1700s in eastern Pennsylvania [10,36]. A current, accurate description of Norway maple distribution in North America is problematic. It is widely planted throughout much of North America, especially along urban streets and in yards. In many areas it escapes into surrounding forest and woodlands, where it may become invasive (see Impacts). Precise distribution information for Norway maple is lacking.
Based on floras and other literature, herbarium samples, and confirmed observations, Norway maple can potentially be found in North America, growing outside cultivation, in the following areas: from New Brunswick and Cape Breton Island west to Minnesota and south to Tennessee and North Carolina. In the West, it is found in British Columbia, Washington, Idaho, and western Montana [8,18,24,34,45,48,52,54,57,63].
Actual distribution of escaped or invasive Norway maple may be more or less broad than the above description. The following description of potential distribution is based on a map developed by Nowak and Rowntree [36] that describes Norway maple performance when grown as an urban street tree. They describe "optimal range" as areas where Norway maple can be grown with few environmental constraints. Although not confirmed as such, these are areas where it is most likely to escape cultivation and potentially become invasive. The "optimal range" in eastern North America is from southern New England south to Chesapeake Bay, the piedmont of southern Virginia and northern North Carolina, and the Appalachians of western North Carolina, South Carolina, and northern Georgia. This distribution continues west through the northern 1/3 of Alabama and Mississippi and the northern 2/3rds of Arkansas to eastern Oklahoma, then north to southeastern South Dakota and southern Minnesota and Wisconsin. Northern limits of this distribution are delineated by western and northern coastal areas of the Great Lakes and the St. Lawrence River. South of this delineation, inland areas of Maine, eastern Quebec, and the southern Maritimes, as well as northern Vermont/New Hampshire and the Adirondacks, are not included in this distribution [36].
The "optimal range" in western North America includes western sections of British Columbia, Washington and Oregon, the North Coast and Sierra regions of California, and northern Idaho/northwestern Montana. Nowak and Rowntree [36] also describe much of the intermountain west and the rest of western and central Montana as "suboptimal range", where some irrigation is required for successful cultivation. Therefore, we might assume that riparian or other mesic habitat is susceptible to invasion in these areas, given a seed source[36].
There is some indication that Norway maple could be potentially invasive in Canada through climate zone 2b.This includes the Maritime provinces, most of Quebec and Ontario, the southern 2/3rds of Manitoba, Saskatchewan, and Alberta, and all but the coldest areas of British Columbia. However, precise distribution data are lacking [43].
The following biogeographic classification systems demonstrate where Norway maple could potentially be found based on the above information. Predicting distribution of nonnative species is difficult due to gaps in understanding of their biological and ecological characteristics, and because they may still be expanding their range. These lists are speculative and may not be accurately restrictive or complete.
Fire adaptations: It is likely that Norway maple increases in the absence of fire. Both sugar maple and red maple, native North American species with similar growth habits and habitat requirements as Norway maple, also increase in the absence of fire.
It is unclear to what extent and at what age Norway maple can survive fire by sprouting.
FIRE REGIMES: As of this writing, it is difficult to identify interactions between Norway maple and particular FIRE REGIMES in North America because distribution of invasive Norway maple is ill-defined. We can probably assume that Norway maple increases in the absence of fire. It is likely that frequent fires would limit Norway maple establishment.
The following table lists fire return intervals for communities or ecosystems throughout North America where Norway maple may occur. This list is presented as a guideline to illustrate historic FIRE REGIMES and is not to be interpreted as a strict description of FIRE REGIMES for Norway maple. Find fire further regime information for the plant communities in which this species may occur by entering the species name in the FEIS home page under "Find FIRE REGIMES".
Community or Ecosystem Dominant Species Fire Return Interval Range (years) silver fir-Douglas-fir Abies amabilis-Pseudotsuga menziesii var. menziesii > 200 grand fir Abies grandis 35-200 [3] maple-beech-birch Acer-Fagus-Betula > 1000 silver maple-American elm Acer saccharinum-Ulmus americana < 35 to 200 sugar maple Acer saccharum > 1000 sugar maple-basswood Acer saccharum-Tilia americana > 1000 Atlantic white-cedar Chamaecyparis thyoides 35 to > 200 [58] Arizona cypress Cupressus arizonica 40] beech-sugar maple Fagus spp.-Acer saccharum > 1000 black ash Fraxinus nigra 58] western juniper Juniperus occidentalis 20-70 Rocky Mountain juniper Juniperus scopulorum 40] western larch Larix occidentalis 25-100 [3] yellow-poplar Liriodendron tulipifera 58] Great Lakes spruce-fir Picea-Abies spp. 35 to > 200 northeastern spruce-fir Picea-Abies spp. 35-200 [11] southeastern spruce-fir Picea-Abies spp. 35 to > 200 [58] blue spruce* Picea pungens 35-200 [3] red spruce* P. rubens 35-200 [11] pine-cypress forest Pinus-Cupressus spp. 3] Rocky Mountain lodgepole pine* Pinus contorta var. latifolia 25-300+ [2,3,46] Sierra lodgepole pine* Pinus contorta var. murrayana 35-200 [3] shortleaf pine Pinus echinata 2-15 shortleaf pine-oak Pinus echinata-Quercus spp. 58] Jeffrey pine Pinus jeffreyi 5-30 western white pine* Pinus monticola 50-200 Pacific ponderosa pine* Pinus ponderosa var. ponderosa 1-47 [3] interior ponderosa pine* Pinus ponderosa var. scopulorum 2-30 [3,6,30] red pine (Great Lakes region) Pinus resinosa 10-200 (10**) [11,16] red-white-jack pine* Pinus resinosa-P. strobus-P. banksiana 10-300 [11,21] pitch pine Pinus rigida 6-25 [9,23] pocosin Pinus serotina 3-8 eastern white pine Pinus strobus 35-200 eastern white pine-eastern hemlock Pinus strobus-Tsuga canadensis 35-200 eastern white pine-northern red oak-red maple Pinus strobus-Quercus rubra-Acer rubrum 35-200 loblolly pine Pinus taeda 3-8 loblolly-shortleaf pine Pinus taeda-P. echinata 10 to < 35 Virginia pine Pinus virginiana 10 to < 35 Virginia pine-oak Pinus virginiana-Quercus spp. 10 to 58] aspen-birch Populus tremuloides-Betula papyrifera 35-200 [11,58] quaking aspen (west of the Great Plains) Populus tremuloides 7-120 [3,20,33] black cherry-sugar maple Prunus serotina-Acer saccharum > 1000 [58] Rocky Mountain Douglas-fir* Pseudotsuga menziesii var. glauca 25-100 [3,4,5] coastal Douglas-fir* Pseudotsuga menziesii var. menziesii 40-240 [3,35,44] oak-hickory Quercus-Carya spp. < 35 northeastern oak-pine Quercus-Pinus spp. 10 to < 35 southeastern oak-pine Quercus-Pinus spp. < 10 white oak-black oak-northern red oak Quercus alba-Q. velutina-Q. rubra 58] canyon live oak Quercus chrysolepis <35 to 200 blue oak-foothills pine Quercus douglasii-Pinus sabiniana 3] northern pin oak Quercus ellipsoidalis 58] Oregon white oak Quercus garryana 3] California black oak Quercus kelloggii 5-30 [40] chestnut oak Quercus prinus 3-8 northern red oak Quercus rubra 10 to < 35 black oak Quercus velutina 58] redwood Sequoia sempervirens 5-200 [3,15,53] western redcedar-western hemlock Thuja plicata-Tsuga heterophylla > 200 [3] eastern hemlock-yellow birch Tsuga canadensis-Betula alleghaniensis > 200 [58] western hemlock-Sitka spruce Tsuga heterophylla-Picea sitchensis > 200 [3] elm-ash-cottonwood Ulmus-Fraxinus-Populus spp. 11,58] *fire return interval varies widely; trends in variation are noted in the species summaryPrescribed fire may or may not be an effective tool for controlling Norway maple. Where physical conditions are sufficient for carrying surface fire, Norway maple presumably can be killed by fire. Although its ecological range in North America is poorly studied, areas where Norway maple is planted and is likely to escape cultivation are subject to a variety of FIRE REGIMES.
In the mixed mesophytic and northern hardwoods ecosystem types of the Northeast, where Norway maple is most commonly reported outside cultivation, fire return intervals range from 35 years to many centuries. Some of these areas, especially those with more frequent fire return intervals and a fire tolerant native flora, may provide suitable conditions for using prescribed fire to control invasive Norway maple.
Fire in mesic forest habitats may spread erratically, leaving a mosaic of burned and unburned patches. Prescribed fire is unlikely to be an effective measure for controlling Norway maple in mesic habitats, since many individuals may remain in unburned patches and other fire refugia.
Effects of fire on colonization and invasive potential of Norway maple are unclear. It does not appear that fire would directly promote an increase in Norway maple recruitment. While there is some indication that seed germination is enhanced by soil disturbance [61], exposure to mineral soil is not a prerequisite for germination [41]. In the presence of a seed source, Norway maple maintains a continuously-recruited seedling population. Dense populations of Norway maple seedlings have been encountered in relatively undisturbed forests in the northeastern United States [31,59,64]. It appears as long as a seed source is nearby, Norway maple can continue to recruit seedlings without regard to disturbance regime. Fire that removes all Norway maple stems, including the seed source, should eradicate it or substantially reduce its presence. Presumably, recolonization of burned areas can only occur if a) a surviving seed source is present within seed dispersal distance, b) prefire genets survive via postfire sprouting, or c) a low-severity or patchy fire results in survival of one or more stems in fire refugia. Fire could possibly increase the invasive potential of Norway maple by removing a substantial portion of the forest canopy, enhancing opportunities for postfire sprouts or seedling colonizers from an off-site seed source to gain canopy dominance. It is unclear how long it may take for Norway maple to spread beyond seed-dispersal distance of a solitary seed source. It is also unclear how long it may take post-fire sprouts to reach sexual maturity. It seems likely that time frames for either scenario would be highly variable and dependent upon the local environment, especially availability of light.
Use of fire in areas where Norway maple is present may or may not be appropriate, depending on management goals and the particular ecosystem involved. Using fire to control Norway maple in forest habitats where fire is infrequent may do substantial damage to fire-intolerant native species, such as sugar maple and American beech [61]. Conversely, fire may be appropriate where management goals simultaneously include controlling Norway maple and maintaining native seral species or otherwise enhancing ecosystem structure and function, such as oak (Quercus spp.) forests in the eastern U.S. or ponderosa pine (Pinus ponderosa) in the northern Rockies. For more information regarding fire effects on native flora, see the appropriate FEIS species summaries on this website.
As of this writing, there is very little published information describing the ecological range of Norway maple in North America. Because Norway maple is commonly mentioned as a congener of sugar maple in eastern North America [1,25,31,59,60,61,64], and because of their taxonomic similarity, it is likely that the two species share a similar ecological range in this region. (See sugar maple for relevant information.)
In Europe, Norway maple occurs within a climatic range characterized by maximum and minimum growing degree days (accumulated temperatures above 5 °C) of 2600 and 1150, respectively [41]. Within this range, it generally occurs in lowland areas, wide river valleys, and low mountain habitats. Norway maple is usually found as individuals or small groups in European mixed forests, and does not form pure stands over large areas [36].
Norway maple grows best on moist, "adequately" drained, deep, fertile soils. It is intolerant of low soil nitrogen conditions and is rare on acidic (pH near 4) soils. Norway maple makes "suboptimum" growth on sandy soils or soils high in lime or clay content, and does not tolerate high evapotranspiration or prolonged drought. Conflicting reports assert that it is rare on poorly drained soils, yet it reportedly can tolerate flooding for up to 4 months [36,41].
Northern distribution of Norway maple in North America is probably limited by cold temperatures. Variation in cold tolerance may be related to genetic source, since many cultivars of Norway maple have been developed for this trait. Seedlings can survive temperatures to at least -12 degrees Fahrenheit (-24 °C), although substantial twig tissue damage can occur. Insulation provided by early-winter snow may reduce seedling damage from cold temperatures [43]. Overwintering flower buds may be killed by prolonged exposure to cold temperatures. In Russia, damage to bud scales and loss of isolated buds have occurred after exposure for 1 hour at temperatures between 23 and 27 degrees Fahrenheit (-5 to -3 °C) and loss of all buds noted below 23 degrees Fahrenheit (-5 °C). Open flowers are more sensitive than buds and may be susceptible to late-season frost. Exposure to temperatures < 27 degrees Fahrenheit (-3 °C) for only 15 minutes produced necrosis in the stigma of the style, and 30 minutes of exposure killed entire flowers [28].
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 informationThere are no reports of the use of Norway maple by North American wildlife, as of this writing, but sugar maple and red maple are browsed by white-tailed deer, moose, and snowshoe hares (see sugar maple and red maple).
Palatability/nutritional value: No information
Cover value: No information
Norway maple is widely planted throughout much of North America. Because it
can produce large numbers of shade-tolerant seedlings, Norway maple may
potentially be found within a variety of forest habitats and plant communities
[36,59,61,64]. It is perhaps best known for its association with the native
sugar maple (Acer saccharum) in the Northeast [31,59,61].
Norway maple is not a climax dominant or indicator species in habitat type
classifications in North America.
Norway maple is a popular landscape and street tree throughout much of the U.S. It is most common in the East and Midwest and less popular in the South [10,19,37,43]. Its popularity is due to its rapid growth, wide site tolerances, attractive autumn foliage, and dense, attractive, shade-providing canopy [10,43].
Wood Products: Norway maple is used sparingly as a lumber species in Europe for veneer and for specialty items such as tool handles, gun stocks and violins [36].
Breeding system: Norway maple is dioecious [12]
Pollination: Norway maple is insect pollinated [36].
Seed production: No information
Seed dispersal: Norway maple seeds are wind-dispersed [28,32,55]. Dispersal distance from seed source is enhanced by winged samaras [28,32]. Estimated lateral distance traveled by samaras in a 6.2 miles/hour (10 km/hr) breeze when dropped from a height of "approximately 3/4 of the maximum height of the species" was 165 feet (50.3 m) [32]. Norway maple samaras dry substantially before dispersal and seeds are desiccation-tolerant thereafter [14]. Seeds are dispersed in fall, which provides a high likelihood of protection under winter snow, conditions usually sufficient for stratification [28].
Seed banking: No information
Germination: Seeds germinate in spring [27,28], following an obligatory period of cold stratification at 37 to 40 degrees Fahrenheit (3-4 °C) for 90-120 days [38,39]. Germination is apparently enhanced by soil disturbance [61], although exposure to mineral soil is not a prerequisite for germination [41].
Seedling establishment/growth: Norway maple produces abundant seedlings each spring [28,29]. First true leaves are formed approximately 3 weeks after seedling emergence [28]. A review of European silvicultural literature characterizes Norway maple seedlings as drought tolerant [41], but other observations indicate that drought resistance of seedlings is low during early development stages [28]. Tolerance to extreme heat or cold is limited during early stages of seedling development. A Russian experiment showed exposure to light frost for 1 hour killed the initial pair of leaves at 28 degrees Fahrenheit (-2 °C) and cotyledons at 25 to 21 degrees Fahrenheit (-4 to -6 °C). Cotyledons and leaves were also killed by exposure to temperatures > 102 degrees Fahrenheit (39 °C) for 2 to 3 hours. Which particular cultivar or variety was used in this experiment is not known [28]. Insulation provided by early-winter snow may reduce seedling damage from cold temperatures [43].
Asexual regeneration: Information concerning the biology of asexual regeneration in Norway maple is sparse and conflicting. USDA Natural Resources Conservation Service Plants Database [54] indicates that at least one cultivar of Norway maple (Crimson King) has the ability to "resprout," but none have "coppice potential." However, Simpfendorfer [50] lists Norway maple, along with sugar maple and red maple (A. rubrum), as species that regenerate by "coppicing" following fire. Postharvest stump sprouting has been documented, although sprouts originating from saplings and smaller trees are apparently hardier than those from mature overstory trees [61]. A review of European autecological data categorizes "tendency to sprouting" for Norway maple as "vigorous" [41].
Norway maple seedlings are characterized as shade tolerant to very shade tolerant. They are often strong competitors in closed-canopy forest understories within the species' North American range [31,60,64]. Seedling growth apparently ceases when light levels fall below 3% of full daylight [22]. Norway maple maintains a continuously recruited "seedling-bank" of persistent, multi-aged seedlings, given a seed source [59,61].
It is likely suppressed Norway maple saplings and seedlings respond favorably following gap formation. In the absence of stand-level disturbance, it is also likely that Norway maple could become a dominant overstory species in eastern deciduous forests where it is established. Along with American beech (Fagus grandifolia) and sugar maple, Norway maple is gradually replacing previously dominant oaks (white oak (Quercus alba), northern red oak (Q. rubra), and black oak (Q. velutina)) in the overstory of a New Jersey piedmont forest [59,60]. Norway maple becomes less shade tolerant with age and mature trees have been characterized as intermediate in shade tolerance [36]. Nevertheless, where it becomes the canopy dominant, Norway maple can suppress regeneration of shade tolerant woody species, including even its own seedlings (see Impacts) [31].
Webb and others [61] raise questions concerning whether Norway maple seedlings are equal to those of sugar maple in persistence, shade tolerance, and response to release, and point out the importance of these questions in determining competitive interactions between the two species. Further research is needed to determine impacts of Norway maple invasion on understory species composition and potential effects on successional trajectories.
The currently accepted scientific name for Norway maple
is Acer platanoides L. (Aceraceae) [18,45,48,52,63].
Over 100 cultivars of Norway maple have been developed for commercial trade in
North America [10,47].
Acer platanoides, commonly known as the Norway maple, is a species of maple native to eastern and central Europe and western Asia, from Spain east to Russia, north to southern Scandinavia and southeast to northern Iran.[2][3][4] It was introduced to North America in the mid-1700s as a shade tree.[5] It is a member of the family Sapindaceae.
Acer platanoides is a deciduous tree, growing to 20–30 m (65–100 ft) tall with a trunk up to 1.5 m (5 ft) in diameter, and a broad, rounded crown. The bark is grey-brown and shallowly grooved. Unlike many other maples, mature trees do not tend to develop a shaggy bark. The shoots are green at first, soon becoming pale brown. The winter buds are shiny red-brown.
The leaves are opposite, palmately lobed with five lobes, 7–14 cm (2+3⁄4–5+1⁄2 in) long and 8–25 cm (3+1⁄4–9+3⁄4 in) across; the lobes each bear one to three side teeth, and an otherwise smooth margin. The leaf petiole is 8–20 cm (3+1⁄4–7+3⁄4 in) long, and secretes a milky juice when broken. The autumn colour is usually yellow, occasionally orange-red.[6][7][8]
The flowers are in corymbs of 15–30 together, yellow to yellow-green with five sepals and five petals 3–4 mm (1⁄8–3⁄16 in) long; flowering occurs in early spring before the new leaves emerge. The fruit is a double samara with two winged seeds. the seeds are disc-shaped, strongly flattened, 10–15 mm (3⁄8–5⁄8 in) across and 3 mm (1⁄8 in) thick. The wings are 3–5 cm (1+1⁄4–2 in) long, widely spread, approaching a 180° angle. It typically produces a large quantity of viable seeds.
Under ideal conditions in its native range, Norway maple may live up to 250 years, but often has a much shorter life expectancy; in North America, for example, sometimes only 60 years. Especially when used on streets, it can have insufficient space for its root network and is prone to the roots wrapping around themselves, girdling and killing the tree. In addition, their roots tend to be quite shallow and thereby they easily out-compete nearby plants for nutrient uptake.[9] Norway maples often cause significant damage and cleanup costs for municipalities and homeowners when branches break off in storms as it does not have strong wood.[10][11]
Leaf, adaxial side
Leaf, abaxial side
Fruit
The Norway maple is a member (and is the type species) of the section Platanoidea Pax, characterised by flattened, disc-shaped seeds and the shoots and leaves containing milky sap. Other related species in this section include Acer campestre (field maple), Acer cappadocicum (Cappadocian maple), Acer lobelii (Lobel's maple), and Acer truncatum (Shandong maple). From the field maple, the Norway maple is distinguished by its larger leaves with pointed, not blunt, lobes, and from the other species by the presence of one or more teeth on all of the lobes.[10][11]
It is also frequently confused with the more distantly related Acer saccharum (sugar maple). The sugar maple is easy to differentiate by clear sap in the petiole (leaf stem); Norway maple petioles have white sap. The tips of the points on Norway maple leaves reduce to a fine "hair", while the tips of the points on sugar maple leaves are, on close inspection, rounded. On mature trees, sugar maple bark is more shaggy, while Norway maple bark has small, often criss-crossing grooves. While the shape and angle of leaf lobes vary somewhat within all maple species, the leaf lobes of Norway maple tend to have a more triangular (acuminate) shape, in contrast to the more finely toothed lobes of sugar maples, that narrow towards the base.[12]: 397 Flowering and seed production begins at ten years of age, however large quantities of seeds are not produced until the tree is 20. As with most maples, Norway maple is normally dioecious (separate male and female trees), occasionally monoecious, and trees may change gender from year to year.
The fruits of Norway maple are paired samaras with widely diverging wings,[12]: 395 distinguishing them from those of sycamore, Acer pseudoplatanus which are at 90 degrees to each other.[12] Norway maple seeds are flattened, while those of sugar maple are globose. The sugar maple usually has a brighter orange autumn color, where the Norway maple is usually yellow, although some of the red-leaved cultivars appear more orange.
The flowers emerge in spring before the leaves and last 2-3 weeks. Leafout of Norway maple occurs roughly when air temperatures reach 55°F (12°C) and there is at least 13 hours of daylight. Leaf drop in autumn is initiated when day lengths fall to approximately 10 hours. Depending on the latitude, leaf drop may vary by as much as three weeks, beginning in the second week of October in Scandinavia and the first week of November in southern Europe. Unlike some other maples that wait for the soil to warm up, A. platanoides seeds require only three months of exposure to temperatures lower than 4 °C (40 °F) and will sprout in early spring, around the same time that leafout begins. Norway maple does not require freezing temperatures for proper growth, however it is adapted to higher latitudes with long summer days and does not perform well when planted south of the 37th parallel, the approximate southern limit of its range in Europe. Further, most North American Norway maples are believed descended from stock brought from Germany, at approximately 48N to 54N, not the more southerly ecotypes found in Italy and the Balkans that evolved for similar lighting conditions as the continental United States. The heavy seed crop and high germination rate contributes to its invasiveness in North America, where it forms dense monotypic stands that choke out native vegetation. The tree is also capable of growing in low lighting conditions within a forest canopy, leafs out earlier than most North American maple species, and its growing season tends to run longer as the lighting conditions of the United States (see above) result in fall dormancy occurring later than it does in the higher latitude of Europe. It is one of the few introduced species that can successfully invade and colonize a virgin forest. By comparison, in its native range, Norway maple is rarely a dominant species and instead occurs mostly as a scattered understory tree.[10][11]
The wood is hard, yellowish-white to pale reddish, with the heartwood not distinct; it is used for furniture and woodturning.[13] Norway maple sits ambiguously between hard and soft maple with a Janka hardness of 1,010 lbf or 4,500 N. The wood is rated as non-durable to perishable in regard to decay resistance.[14] In Europe, it is used for furniture, flooring and musical instruments. This species as grown in the former Yugoslavia is also called Bosnian maple, and is probably the maple used by the famous Italian violin makers, Stradivari and Guarneri.
Norway maple has been widely taken into cultivation in other areas, including western Europe northwest of its native range. It grows north of the Arctic Circle at Tromsø, Norway. In North America, it is planted as a street and shade tree as far north as Anchorage, Alaska.[15] In Ontario, it is common in cultivation north to Sault Ste. Marie and Sudbury; although not considered reliably hardy northward, it has been established at Kapuskasing and Iroquois Falls, and even at Moose Factory.[16] It is most recommended in USDA Hardiness Zones 4 to 7 but will grow in warmer zones (at least up to Zone 10) where summer heat is moderate, as along the Pacific coast south to the Los Angeles basin. They tend to prefer wetter Oceanic climates. [17] During the 1950s–60s it became popular as a street tree due to the large-scale loss of American elms from Dutch elm disease.
It is favored due to its tall trunk and tolerance of poor, compacted soils and urban pollution, conditions in which the sugar maple has difficulty. It has become a popular species for bonsai in Europe, and is used for medium to large bonsai sizes and a multitude of styles.[18] Norway maples are not typically cultivated for maple syrup production due to the lower sugar content of the sap compared to sugar maple.[19]
Many cultivars have been selected for distinctive leaf shapes or colorations, such as the dark purple of 'Crimson King' and 'Schwedleri', the variegated leaves of 'Drummondii', the light green of 'Emerald Queen', and the deeply divided, feathery leaves of 'Dissectum' and 'Lorbergii'. The purple-foliage cultivars have orange to red autumn colour. 'Columnare' is selected for its narrow upright growth.[11][20] The cultivars 'Crimson King'[21] and 'Prigold' (Princeton Gold)[22] have gained the Royal Horticultural Society's Award of Garden Merit.
The Norway maple was introduced to northeastern North America between 1750 and 1760 as an ornamental shade tree. It was brought to the Pacific Northwest in the 1870s.[5] Today, Norway maples tend to be most common in the Pacific Northwest, in southern Ontario, and along the Kennebec river in southern Maine. The roots of Norway maples grow very close to the ground surface, starving other plants of moisture. For example, lawn grass (and even weeds) will usually not grow well beneath a Norway maple, but English Ivy, with its minimal rooting needs, may thrive. In addition, the dense canopy of Norway maples can inhibit understory growth.[23] Some have suggested Norway maples may also release chemicals to discourage undergrowth,[24] although this claim is controversial.[23] A. platanoides has been shown to inhibit the growth of native saplings as a canopy tree or as a sapling.[23] The Norway maple also suffers less herbivory than the sugar maple, allowing it to gain a competitive advantage against the latter species.[25] As a result of these characteristics, it is considered invasive in some states,[26] and has been banned for sale in New Hampshire[27] and Massachusetts.[28] The state of New York has classified it as an invasive plant species.[29] Despite these steps, the species is still available and widely used for urban plantings in many areas.
Education about the invasive nature of the tree is expanding thanks to organizations like the National Audubon Society.[30]
Fruit (samara): note the flat seed capsule and the angle of the "wings"
Typical yellow fall foliage
Atypical orange-red fall colour
Purple leaves of cultivar 'Schwedleri'
Twig and buds
The larvae of a number of species of Lepidoptera feed on Norway maple foliage. Ectoedemia sericopeza, the Norway maple seedminer, is a moth of the family Nepticulidae. The larvae emerge from eggs laid on the samara and tunnel to the seeds. Norway maple is generally free of serious diseases, though can be attacked by the powdery mildew Uncinula bicornis, and verticillium wilt disease caused by Verticillium spp.[31] "Tar spots" caused by Rhytisma acerinum infection are common but largely harmless.[32] Aceria pseudoplatani is an acarine mite that causes a 'felt gall', found on the underside of leaves of both sycamore maple (Acer pseudoplatanus) and Norway maples.[33]
Acer platanoides, commonly known as the Norway maple, is a species of maple native to eastern and central Europe and western Asia, from Spain east to Russia, north to southern Scandinavia and southeast to northern Iran. It was introduced to North America in the mid-1700s as a shade tree. It is a member of the family Sapindaceae.
