Norway Maple
Suggested Citation: Doroski, Danica A.; Keriö, Susanna E.; Wegrzyn, Jill L.; Ward, Elisabeth B. 2026. Norway maple (Acer platanoides). In: McNulty, Steven; Callaham, Mac A., Jr., project co-leads. Silvics of North America. U.S. Department of Agriculture, Forest Service; Natural Resources Canada, Canadian Forest Service; National Forestry Commission of Mexico, collaborators. Washington, DC: U.S. Department of Agriculture, Forest Service. https://doi.org/10.2737/sna.acer.platanoides.
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- Steven McNulty, Project Lead (USDA Forest Service)
- Mac A. Callaham, Jr., Program Manager (USDA Forest Service)
- Rachel Cook, Principal Investigator (North Carolina State University)
- Emma Gates, U.S. Project Coordinator (Three Vowels, LLC)
- Sébastien Meunier, Canada Project Coordinator (Canadian Forest Service)
- Cynthia F. Moser, Managing Editor (Three Vowels, LLC)
- Michael Gavazzi, Content Coordinator (U.S. Forest Service)
- Brody Hall, Business Administrator (North Carolina State University)
Acer platanoides is identified as a widespread invasive species in North America. Management and utilization of this species should be carried out in accordance with local, regional, and national regulations. Please note the following classifications present at the time of publication:
- Federal Government Documents
- United States of America: Listed as an introduced and widespread invasive (Category E) by the U.S. Geological Survey (USGS) “United States Register of Introduced and Invasive Species” (US-RIIS; Simpson et al., 2022)
- Canada: None available at this time
- Mexico: None available at this time
- National (nongovernmental) Assessments
- Reported to be invasive in natural areas (Swearingen and Bargeron, 2016)
Please see the following links to regional, Provincial, State, and local listings highlighting invasive nonnative classifications. Note that this list may not be comprehensive.
- Invasive Plant Atlas of the United States: University of Georgia, Center for Invasive Species and Ecosystem Health (n.d.). Norway maple. https://www.invasive.org/browse/subinfo.cfm?sub=3002#list
- PLANTS Database: U.S. Department of Agriculture, Natural Resources Conservation Service (n.d.). Acer platanoides L. https://plants.usda.gov/plant-profile/ACPL/noxious-invasive
- Connecticut—Invasive: University of Connecticut (n.d.). Connecticut invasive plant list. https://cipwg.uconn.edu/iinvasive_plant_list/
- Delaware—Invasive: Delaware Invasive Species Council (2026). Plants. https://delawareinvasives.net/blog1/?page_id=68
- Indiana—Invasive: Purdue University College of Agriculture (2026). Norway maple. Indiana Invasive Species Norway Maple (purdue.edu)
- Maine—Do Not Sell: Maine Department of Agriculture, Conservation, & Forestry (2018). Maine invasive plants. Invasive Plants: Horticulture: APH: Maine ACF
- Maryland—Invasive: Maryland Invasive Species Council (2005). Invasive species of concern in Maryland. 2005_brochure_rev (mdinvasives.org)
- Massachusetts—Prohibited: Massachusetts Department of Agricultural Resources (2026). Massachusetts prohibited plant list. Massachusetts Prohibited Plant List | Mass.gov
- Michigan—Invasive: Michigan State University (2026) Norway maple (Acer platanoides). Norway maple: Acer platanoides - Aceraceae (Maple) (msu.edu)
- Minnesota—Specially Regulated: Minnesota Department of Agriculture (2020). 2020 Noxious weed list. 2020 Noxious Weed List (state.mn.us)
- New Hampshire—Prohibited: New Hampshire Department of Agriculture, Markets, and Food (n.d.). Chapter Agr 3800 invasive species. Agr 3800 (state.nh.us)
- New Jersey—Prohibited: New Jersey Office of Legislative Services (2026). Assembly, No. 3677 State of New Jersey 220th legislature. NJ Legislature (state.nj.us)
- New York—Regulated: NY Department of State-Division of Administrative Rules (2023). 575.4 Regulated invasive species. View Document - New York Codes, Rules and Regulations (westlaw.com)
- Ohio—Potentially Invasive: Ohio Invasive Plants Council (2016). OIPC plant assessment results. ASSESSMENT RESULTS - Ohio Invasive Plants Council (oipc.info)
- Ontario—Invasive: Ontario Invasive Plant Council (2026). Species. https://www.ontarioinvasiveplants.ca/invasive-plants/species/
- Pennsylvania—Invasive: Commonwealth of Pennsylvania (2026). Invasive plant fact sheets. Invasive Plant Fact Sheets (pa.gov)
- Vermont—Class B Noxious Weed: Vermont Agency of Agriculture, Food & Markets (2026). Designated noxious weeds. Designated Noxious Weeds | Agency of Agriculture Food and Markets (vermont.gov)
- Virginia—Invasive: Virginia Department of Conservation and Recreation, Division of Natural Heritage (2024). Virginia invasive plants species list. nh-invasive-plant-list-2023.pdf (virginia.gov)
- West Virginia—Invasive: West Virginia DNR (2009). Invasive plant species of West Virginia. Handout-Invasive-Plants-of-WV-2009.pdf (wvdnr.gov)
- Wisconsin—Invasive: Invasive Plant Association of Wisconsin (n.d.). Invasive Plant Association of Wisconsin. IPAW's Plant List - Invasive Plants Association of Wisconsin
Pesticide Disclaimer
This publication/database reports research involving pesticides. It does not contain recommendations for their use, nor does it imply that the uses discussed here have been registered. All uses of pesticides must be registered by appropriate State and/or Federal agencies before they can be recommended.
CAUTION: Pesticides can be injurious to humans, domestic animals, desirable plants, and fish or other wildlife—if they are not handled or applied properly. Use all pesticides selectively and carefully. Follow recommended practices for the disposal of surplus pesticides and pesticide containers.
Norway maple (Acer platanoides; figs. 1 through 5) is one of the most prolific nonnative tree species in the United States. Originally introduced to the United States from Europe in the mid-1700s, Norway maple is among the most common street trees in the northeastern, midwestern, and western United States (Ma et al., 2020). It was once favored for its ability to grow in various environments, including a high tolerance for urban conditions such as air pollution (Dirr, 2009). It has since fallen out of favor due not only to its ability to escape cultivation, but also to structural issues such as weak limbs, poor branch attachment (Tothill and Slater, 2019), and susceptibility to decay, Verticillium wilt, canker pathogens, and foliar disease (Luley, 2022; Sinclair and Lyon, 1987).
Norway maple grows well in both open and densely shaded areas, exhibiting both mid- and late successional growth traits. These traits, in addition to earlier leaf-out and later leaf senescence, reduced pressure from aggressive pathogens and pests (enemy release hypothesis), greater photosynthetic capacity, and greater stem diameter growth than native maple species, have enabled invasions in both open areas and intact forests. Norway maple poses a significant threat to forests throughout its naturalized range and is associated with decreases in understory species richness (Galbraith-Kent and Handel, 2012; Martin, 1999; Wyckoff and Webb, 1996), reduced regeneration of native trees (Martin, 1999; Reinhart et al., 2005; Webb et al., 2001), and altered soil conditions (Galbraith-Kent and Handel, 2012; Gómez-Aparicio et al., 2008; Reinhart et al., 2006).
Figure 1—Norway maple (A) leaves and (B) leaf sap in New Haven, Connecticut, August 2024. Norway maple leaves are opposite, five-lobed, and sharply pointed. Norway maple leaves are similar in appearance to sugar maple but can be distinguished by the milky white sap exuded when the petiole is removed from the stem. Courtesy photos by Danica Doroski.
Figure 2—Norway maple bark in New Haven, Connecticut, August 2024. When young, most maple species have grayish smooth bark, making it difficult to distinguish between species. As Norway maple matures, its bark forms narrow, intersecting ridges that are often diamond shaped and can be used to distinguish mature Norway maples from other maple species. Courtesy photo by Danica Doroski.
Figure 3—Planted Norway maple in New Haven, Connecticut, September 2023. Norway maple is a medium- to large-sized tree planted abundantly as a landscape and street tree throughout the northeastern, midwestern, and western United States. Courtesy photo by Susanna Keriö.
Figure 4—Stand of Norway maple saplings in New Haven, Connecticut, August 2024. Norway maple has escaped cultivation and can be found naturalizing in intact forest stands and open areas throughout the northeastern and midwestern United States and in southeastern Canada. Where it occurs, it often forms monocultures like the roadside population pictured here. Courtesy photo by Danica Doroski.
Figure 5—Tar spot on Norway maple leaf in New Haven, Connecticut, August 2024. Black spots, or tar spot, is a fungal disease commonly found on Norway maple leaves in late summer and fall. These black spots can also help distinguish Norway maple from other maple species. Courtesy photo by Susanna Keriö.
Distribution
Norway maple is native to continental Europe and western Asia (Nowak and Rowntree, 1990) and is the most widespread maple species in central and northern Europe (Matisone et al., 2024). Norway maple was first introduced to North America by John Bartram in 1756 (Nowak and Rowntree, 1990). It has been planted widely as a street and yard tree throughout the United States and Canada and is among the three most common street trees in the northeastern (16.5 percent of street trees), midwestern (4.9 percent of street trees), and western (3.8 percent of street trees) United States (Ma et al., 2020).
Norway maple has escaped cultivation and can be found naturalizing throughout the northeastern and midwestern regions of the United States and Canada (fig. 6). Specifically, Norway maple has naturalized in Canada through Ontario and Prince Edward Island. Within the United States, the species has naturalized throughout New England, New York, Pennsylvania, and the mid-Atlantic States, extending southward to Virginia, and with scattered populations in Kentucky and West Virginia. Norway maple can also be found throughout the midwestern United States, extending to Minnesota and into a small area of Iowa and Nebraska. A few outlier communities are found in the southern United States in Georgia and Alabama, as well as the western United States in Washington, Oregon, and Montana.
Figure 6—Current distribution of Norway maple as reported in the citizen science platforms EDDMapS and iNaturalist, and national forest inventory data from the United States (U.S. Forest Service, Forest Inventory and Analysis) and Canada (National Forest Inventory). U.S. Forest Service cartography by Jacob Fraser.
Depending on the region, the migration or invasion potential of Norway maple can be affected by minimum temperature, precipitation, and soil properties. Most of the data on projected distribution are from the native range and may not be fully applicable to North America. Cold winter temperatures remain a limiting factor for northward expansion. In Sweden, under a projected global warming of 3.6 °C (6.5 °F; moderate to high carbon dioxide emissions), from 2041 to 2071 Norway maple is predicted to utilize river valleys with suitable soil pH for northward expansion. From 2071 to 2100, the species is predicted to continue to spread to higher altitudes as minimum temperatures increase (Souza Lima et al., 2024). Invasion of higher elevation sites through river valleys could be applicable to the Great Lakes region, Ontario and Quebec, the Adirondack Mountains, the Appalachian Mountains, and parts of New England. In the warming scenarios, northward spread could be limited by spring frosts, especially in maritime areas (Ma et al., 2019). In southeastern Germany under a projected global warming of 4 °C (7 °F; high carbon dioxide emissions), the climatically suitable area for Norway maple is predicted to decrease by 2070 to 2100 (Fäth et al., 2025).
Environmental Associations
Norway maple is limited primarily by precipitation and is not found in regions that receive less than an average of 220 mm (9 inches) of precipitation annually (table 1). The mean annual precipitation in Norway maple’s introduced range is 1100 mm (43 inches), and the mean maximum is 3100 mm (123 inches).
Norway maple is also limited by temperature; the mean annual temperature in Norway maple’s introduced range is 9 °C (48 °F) (table 1). Minimum mean annual temperature is 1 °C (34 °F), and the maximum is 17 °C (63 °F). Norway maple is considered hardy in U.S. Department of Agriculture Plant Hardiness Zones 4b to 7b. However, field trials in Zone 2 (Canadian Zone 2b) indicate that Norway maple can be grown in this zone with limited cold damage (Richer-Leclerc et al., 1994). Frost injury in late fall to early winter is a more common issue of cold hardiness than insufficient mid-winter hardiness or early bud flushing in the spring (Pagter et al., 2010). Norway maple cold hardiness is also related to variation in minimum and maximum daily temperatures, with more extreme temperature variation correlating with increased winter injury (Dirr, 2009; Kjelgren et al., 1997; Richer-Leclerc et al., 1994). Richer-Leclerc et al. (1994) also detected a correlation between seedling twig damage and the absence of snow cover in early winter, indicating that snow insulation provides protection for Norway maple seedlings. Maximum temperature may also impact Norway maple’s geographic range. Seed viability decreases in warmer and drier climates within its native range (Carón et al., 2014) and warm nighttime temperatures in the summer can retard the growth of established trees in its introduced range (Dirr, 2009).
In its native range, Norway maple is primarily a lowland species found growing in river valleys and low mountainous areas (Nowak and Rowntree, 1990). In the United States and Canada, it is widespread, with a mean elevation of 320 m (1,050 feet) and an elevation range from sea level to 2730 m (8,940 feet) (table 1). Naturalized populations at higher elevations (e.g., over 1000 m [3,280 feet]) are typically found in the western United States (Reinhart et al., 2006).
Table 1—Temperature, precipitation, and elevation ranges for Norway maple in North America
| Summary statistics (actual, 1991–2020) | Mean annual temperature in °C (°F) | Mean annual precipitation in millimeters (inches) | Elevation in meters (feet) |
| Minimum | 1.4 (35) | 220 (9) | Sea level |
| Lower 25 percent | 7.1 (45) | 950 (38) | 160 (510) |
| Median | 8.8 (48) | 1090 (43) | 240 (790) |
| Mean | 8.8 (48) | 1090 (43) | 320 (1,050) |
| Upper 25 percent | 10.5 (51) | 1240 (49) | 350 (1,150) |
| Maximum | 17.1 (63) | 3120 (123) | 2730 (8,940) |
Soils in Norway maple's naturalized range are primarily Spodosols, Inceptisols, and Alfisols. Norway maple prefers mesic sites with deep, fertile, well-drained, loamy soils (Nowak and Rowntree, 1990) but can be found in both sandy and clay soils (Richer-Leclerc et al., 1994). Norway maple is thought to be more adapted to a range of soil conditions than the native red maple (Acer rubrum) (Galbraith-Kent and Handel, 2012) and to drier soils than the native sugar maple (Acer saccharum) (Dirr, 2009). In the western United States, Norway maple spread is limited by inadequate soil moisture (Reinhart et al., 2006). While many tree reference manuals and horticultural guides tout Norway maple for its ability to thrive in nearly any soil type (Dirr, 2009), there is limited empirical research to support these claims (Sjöman and Busse Nielsen, 2010).
Norway maple prefers soils with a pH of 5.5 to 6.5 (Nowak and Rowntree, 1990). This is similar to the pH preferences of sugar maple (Godman et al., 1990) but more limited than red maple (Walters and Yawney, 1990). While Norway maple prefers moderately acidic to neutral soils, high seedling survivorship has been found in base-rich soils, up to 7.5 pH (Martin and Marks, 2006). Seedling emergence and survival are lowest in strongly acidic soils (pH lower than 4.5) (Martin and Marks, 2006).
Sexual Reproduction
Norway maple fruit is a double-winged samara that ripens in the fall (September and October) and is dispersed primarily by wind (Hong and Ellis, 1992) and, less frequently, by water (Säumel and Kowarik, 2010). Seeds are typically 3.5 to 5.0 cm (1.4 to 2.0 inches) long with a 1-cm (0.4-inch) chord. Dried seed mass ranges from 100 to 200 mg (Molteno, 2022), though seed traits may shift with climatic conditions (Carón et al., 2014). A study along a 2200-km (1,370-mile) latitudinal gradient in Norway maple’s native range found that a 4.8 °C (8.6 °F) increase in temperature reduced seed nitrogen concentrations by 13 percent and seed mass by 33 percent (Carón et al., 2014). In the same study, a 460-mm (18-inch) difference in annual rainfall reduced seed potassium concentrations by 34 percent. Overall, Norway maple seed viability decreased by 38 percent from the coldest and wettest provenances to the warmest and driest (Carón et al., 2014).
Norway maple has dish-shaped flowers consisting of five yellowish-green sepals and petals. The flowers are perfect and approximately 1 cm (0.4 inch) in diameter (Weryszko-Chmielewska and Sulborska, 2011). Norway maple is monoecious (Liesebach and Schneck, 2022). In the open, Norway maple typically starts flowering at 10 to 15 years. In the forest, flowering starts later, at 25 to 30 years (Liesebach and Schneck, 2022). Flowers emerge before or at the same time as leaves in the spring. In North America, this can range from mid-April (Finch-Savage et al., 1998) to May (Reinhart et al., 2006), depending on location.
Norway maple is insect pollinated (Liesebach and Schneck, 2022). Pollen loads on mature Norway maple from Ann Arbor, Michigan, averaged 863 pollen anther-1 ± standard deviation (SD) 516, 8 anthers flower-1 ± SD 0, and 41.2 flowers bud-1 ± SD 19 (Katz et al., 2020).
Norway maple typically starts bearing seed at 25 to 30 years (Gordon and Rowe, 1982). Heavy seed crops are produced every 1 to 3 years (Gordon and Rowe, 1982) and are shed in the fall (Hong and Ellis, 1990). Seed quantity can vary significantly from year to year but is generally considered “unremarkable” compared with other native tree species in the northeastern United States (Martin and Canham, 2010). In one study, seed quantity ranged from 2,203 seeds tree-1 in one year to 8,452 seeds tree-1 in another (Martin and Canham, 2010). Once Norway maple reaches the minimum diameter at breast height (DBH) for seed production, seed quantity is similar, irrespective of tree size (Martin and Canham, 2010). Notably, in Norway maple, this minimum size (11.6 cm [4.6 inches DBH]) is smaller than other native tree species such as red maple, American beech (Fagus grandifolia), black cherry (Prunus serotina), and red oak (Quercus rubra), which do not bear seed until they attain a minimum DBH of 21.6 to 44.0 cm (8.5 to 17.3 inches) (Martin and Canham, 2010).
Norway maple seeds can travel approximately 50 to 60 m (160 to 200 feet) from parent trees in a light breeze (10 km hour-1 [6.2 miles hour-1]) (Matlack, 1987), though dispersal distances up to several hundred meters have been suggested (Bertin et al., 2005). Other studies in closed-canopy forests have found significantly less dispersal potential with an average maximum dispersal distance of 13 to 15 m (43 to 49 feet) (Martin and Canham, 2010). This relatively short dispersal distance suggests that Norway maple is somewhat dispersal limited in closed-canopy forests. Compared with native red maple, Norway maple has a much higher seed mass, resulting in a dispersal distance of approximately half that of red maple (Matlack, 1987). Norway maple seed mass is also 65 percent greater than the native sugar maple. However, its terminal velocity is also slower than sugar maple’s, which allows for a greater dispersal potential despite its higher seed mass (Meiners, 2005).
Norway maple seeds germinate in the spring after a period of cold stratification at 3 to 4 °C (37 to 39 °F) for 90 to 120 days (Dirr, 2009). Seeds have orthodox (desiccation-tolerant) storage behaviors (Finch-Savage et al., 1998). Germination rates after 100 to 120 days in controlled greenhouse experiments range from 78 to 82 percent (Finch-Savage et al., 1998). Germination rates as high as 92 percent have been recorded for seeds hermetically stored at 0 °C (32 °F) for a year (Hong and Ellis, 1990). However, experiments with Norway maple cultivars suggest much lower germination rates of 0 to 35 percent (Conklin and Sellmer, 2009).
In situ emergence rates are lower than in controlled germination studies. Field studies using Norway maple cultivars had a 0 to 23 percent germination rate when sown in open fields and a 0 to 18 percent germination rate in forest floor sites (Conklin and Sellmer, 2009). A 3-year study in closed-canopy forest and forest gaps found that annual germination rates ranged from 8.9 to 19.3 percent and averaged 14.7 percent over the course of the study (Martin and Marks, 2006). These rates are lower than the controlled germination studies listed earlier but on par with field-based germination rates for sugar maple (Meiners, 2005).
Germination is promoted by soil disturbance (Bertin et al., 2005; Webb et al., 2001). Once germinated, the minimum time to seedling (seedling is defined as greater than 5 cm [2 inches] in height) is 5 years, with a mean height of 9.1 ± SD 3.2 cm (3.6 ± 1.3 inches), though maximum height growth will be higher in gaps (Martin and Marks, 2006). Norway maple seedlings are 98 percent larger than sugar maple seedlings due to Norway maple's larger seed size (Meiners, 2005). However, size differences between these two species may diminish over time (Morrison and Mauck, 2007). Seedling survivorship is 93 percent in deep shade and 98 percent in small gaps (Martin and Marks, 2006). The ability of seedlings to persist even in deep shade suggests that Norway maple, like sugar maple, is a seedling bank species (Martin and Canham, 2010). Higher soil pH (greater than 6) is associated with increased seedling survivorship, particularly in deep shade conditions (Martin and Marks, 2006).
There is a long lag between seedling establishment and sapling recruitment; the time to first sapling (sapling is defined as 1.4 m [4.6 feet] in height) is 40 years in the shade and 23 years in gaps (Martin and Marks, 2006). Both seedlings and saplings are highly shade-tolerant; even in deeply shaded, acidic conditions, approximately 1 percent of seeds emerge and survive to become saplings (Martin and Marks, 2006).
Asexual Reproduction
Norway maple is not known to regenerate via root sprouts or layering (Nicolescu et al., 2018). However, it is a prolific stump sprouter (Prentice and Helmisaari, 1991; Webb et al., 2001; Webster et al., 2007).
Stump sprouting can occur on saplings and mature trees, but sprout survivorship decreases with tree size (Webb et al., 2001). Norway maple is difficult to propagate from cuttings, but vegetative propagation can be accomplished with etiolation, by taping the cut ends of the etiolated shoots, and by dipping the shoots in indole-3-butyric acid (IBA) to stimulate root development (Tomov, 2017). In nurseries, propagation of Norway maple cultivars such as ‘Crimson King’ is done by budding, where buds of the desired cultivar are grafted onto Norway maple seed rootstock. The highest success rates for bud-take are achieved on field-grown rootstocks with unrestricted root growth and in noncompacted soils or sand beds (Howard and Oakley, 1997). Norway maple cultivars can also be multiplied clonally by micropropagation (Lattier et al., 2013).
Within Norway maple’s native range of continental Europe and western Asia, Norway maple is classified as a “scattered broad-leafed species” or a “secondary species” (Caudullo and de Rigo, 2016). These are species with scattered distributions in mixed forests, rarely exceeding 3 percent of the forest cover (Hemery et al., 2010).
In North America, Norway maple has been planted abundantly as an ornamental and street tree in the northeastern, midwestern, and western United States (Ma et al., 2020) as well as southeastern Canada (Simkovic, 2020; Turner et al., 2005). Where Norway maple has been planted, it has naturalized and become a component of various forest community types in urban and exurban areas. In the western United States (Montana), Norway maple is associated with the native Douglas-fir (Pseudotsuga menziesii) forest type (Reinhart et al., 2006). In the midwestern United States, Norway maple has been found in mixed conifer-hardwood stands comprising northern white cedar (Thuja occidentalis), white spruce (Picea glauca), paper birch (Betula papyrifera), sugar maple, American beech, and ironwood (Ostrya virginiana) (Wangen et al., 2006; Webster et al., 2005). In the northeastern United States, Norway maple is found in oak-hickory (Doroski et al., 2022; Morrison and Mauck, 2007), mixed oak (Galbraith-Kent and Handel, 2012), and beech-oak-sugar maple forest types (Webb and Kaunzinger, 1993). Norway maple is also common in early-successional forest patches consisting of silver maple (Acer saccharinum), boxelder maple (Acer negundo), hackberry (Celtis occidentalis), white ash (Fraxinus americana), black locust (Robinia pseudoacacia), black birch (Betula lenta), black cherry (Prunus serotina), and slippery elm (Ulmus rubra) in the northeastern United States (Doroski et al., 2022; Martin, 1999; Morrison and Mauck, 2007). In Ontario, Norway maple has naturalized in mixed hardwood stands consisting of sugar maple, white cedar, black cherry, American beech, eastern hemlock (Tsuga canadensis), and red oak (Postma, 2020).
Within both its native and introduced range, Norway maple is considered a late successional and shade-tolerant species. Despite this classification, Norway maple diverges from traditional life-history tradeoff patterns by combining high growth rates with high shade tolerance, acting as both a mid- and late successional species (Martin et al., 2010).
Though generally considered a late successional species, Norway maple is competitive in large gaps and recently disturbed areas (Anderson, 1999; Bertin et al., 2005). A retroactive analysis of the stand dynamics in a Norway maple population in Michigan found that most of the overstory Norway maples established under open-canopy conditions (Webster et al., 2005). Norway maple seedlings exhibit greater photosynthetic capacity, greater stem diameter growth, greater aboveground biomass, an extended growth period compared with sugar maple in canopy gaps (Paquette et al., 2012), and greater height growth than sugar and red maple in large canopy gaps (Martin et al., 2010).
While highly competitive in open-canopy conditions, Norway maple’s high degree of phenotypic plasticity enables it to compete in low-light conditions as well (Lei and Lechowicz, 1998; Paquette et al., 2012). In both “small canopy gap” and “moderate shade” conditions (10 and 5 percent light transmittance, respectively), Norway maple seedlings exhibit higher survival and height growth rates than sugar and red maple (Martin et al., 2010). Norway maple’s competitive advantage persists in closed-canopy forest, where it exhibits higher rates of photosynthesis (Morrison and Mauck, 2007) and diameter growth than sugar maple (Paquette et al., 2012). Only in the deepest shade (2 percent light transmittance) does sugar maple obtain a competitive edge, exceeding Norway maple in growth and survivorship (Martin et al., 2010).
The ability to establish and compete in closed-canopy forests has enabled Norway maple to proliferate in intact forests as well as in canopy gaps. Norway maple has been found in closed-canopy oak-hickory forests in New Jersey (Webb and Kaunzinger, 1993), Massachusetts (Bertin et al., 2005), and Connecticut (Doroski et al., 2022). In these stands, Norway maple is present primarily in the seedling and sapling size classes and is found at significantly higher densities than other native tree species (Bertin et al., 2005; Martin and Canham, 2010; Webb and Kaunzinger, 1993). For example, Wyckoff and Webb (1996) found that 81 percent of regeneration in a sugar maple stand was Norway maple compared with only 14 percent sugar maple regeneration. Thus, even intact forests with native-dominated canopies may shift over time to Norway maple-dominated forest types if Norway maple is present in the seedling and sapling size classes.
Where these successional shifts occur, there are likely to be profound impacts on the long-term structure and composition of the forest. Once established in the canopy, Norway maple has been found to facilitate its own regeneration. Specifically, Norway maple seedling biomass may be greater (Galbraith-Kent and Handel, 2012), seedlings may be more shade-tolerant (Fang and Wang, 2011), and overall seedling abundance may be greater (Reinhart et al., 2006; Wyckoff and Webb, 1996) under conspecific versus heterospecific canopies. This is likely due to positive plant-soil feedbacks (Fang and Wang, 2011) such as increased soil pH (Gómez-Aparicio et al., 2008) and a favorable microclimate (Reinhart et al., 2006). On the other hand, it has been hypothesized that in dense Norway maple stands, Norway maple growth may be limited by the accumulation of negative soil biota, pathogens, and pests (Gómez-Aparicio et al., 2008; Martin and Canham, 2010; Martínez-García et al., 2016) or creation of dense shade (Martin, 1999). However, the composition of potentially inhibitory soil communities is largely unknown (DeBellis et al., 2019) and comparisons of understory light conditions between Norway maple canopy and other canopy types have not discerned significant differences in understory light regimes (Fang and Wang, 2011; Reinhart et al., 2006). In this context, it is worth noting that even in dense monocultures in North America, Norway maple has relatively low rates of herbivory (Clem and Held, 2018) and fungal disease compared with rates in its native range (Adams et al., 2009).
Irrespective of any facilitatory or inhibitory mechanisms on its own regeneration, Norway maple has been found to inhibit natural regeneration of many common native species and limit understory diversity. The biomass of red maple leaves, shoots, and roots was found to be significantly lower when the trees were grown beneath Norway maple-dominated canopy compared with native canopy (Galbraith-Kent and Handel, 2012). Tree species richness is also reduced in Norway maple stands (Galbraith-Kent and Handel, 2012; Wyckoff and Webb, 1996). For example, Martin (1999) found that only two sapling and three seedling species grew beneath Norway maple canopies compared with seven sapling and seven seedling species beneath sugar maple canopies. Allelopathy has been suggested as one of the mechanisms reducing richness and regeneration under Norway maple canopy (Sujeeun and Thomas, 2023). However, the research on Norway maple's allelopathic potential is conflicting; see the Knowledge Gaps section.
Norway maple is generally classified as a fast-growing species. Saplings have a height increment of approximately 1 m year-1 (3 feet year-1) in Norway maple’s native range (Caudullo and de Rigo, 2016). In North America, annual height growth increments for saplings are less at 19.26 ± standard error (SE) 3.22 cm (7.58 ± 1.27 inches), though notably, this is almost double the height growth increment of sugar maple at 10.01 ± SE 1.69 cm (3.94 ± 0.67 inches) (Kloeppel and Abrams, 1995). Cumulative height growth rates average 0.39 ± SD 0.02 m year-1 (1.28 ± 0.07 feet year-1) for forest-grown trees and 0.49 ± SD 0.07 m year-1 (1.61 ± 0.23 feet year-1) for open-grown trees (Webster et al., 2005).
Norway maple growth rates shift with light availability but still exceed native maple growth in most cases. In simulated gaps with a light transmittance of 80 percent (“very high light”), Norway maple took only 3.4 years to reach 3 m (10 feet) in height as compared with sugar maple at 16.6 years and red maple at 12.3 years (Martin et al., 2010; though note that these findings contrast with Fang and Wang, 2011). Once established, Norway maple is able to recruit into the overstory before other native tree species (12 to 22 years before sugar maple and 31 years before American beech (Webster et al., 2005). In lower light conditions (e.g., 10 and 5 percent light transmittance), Norway maple continues to obtain more rapid height growth than native tree species. Only in “deep shade” (2 percent light transmittance) does sugar maple exceed Norway maple in height growth (time to 3 m in height is 21.2 years versus 31.5 years for sugar and Norway maple, respectively) (Martin et al., 2010).
Saplings average less than 1 mm year-1 (0.04 inch year-1) in recent and cumulative radial growth. As Norway maple reaches the canopy, radial growth patterns suggest that their growth rate rapidly decreases (Tomov et al., 2014; Webster et al., 2005).
Management with Natural Regeneration
Norway maple is not a tree species that land managers promote in North American forests. As such, there is no published information outlining management techniques for the establishment and growth of Norway maple through silvicultural systems in nonurban forests in this region (as of 2025). Instead, management recommendations focus on its suppression and control to promote the growth of co-occurring native tree species (see appendix A.1, Management to Control). This publication therefore highlights silvicultural research from Norway maple’s native range or from its native congener in North America, sugar maple. Even within Europe, silvicultural management of Norway maple is limited compared to sycamore maple (Acer pseudoplatanus), which has similar traits and silvicultural requirements (Evans, 1984; Forest Research, 2016; MacDonald et al., 1957; Savill, 2013).
Although Norway maple tolerates heavy shade in the seedling and sapling stages, it does require light to advance into the canopy (CABI, 2019; Nisbet, 1893). Management for Norway maple should, therefore, focus on attaining advanced regeneration in the understory and then promoting more rapid growth through partial harvesting systems that create uneven-aged, mixed-species stands, which is similar to management recommendations for sugar maple in North America (Danyagri et al., 2019). Even-aged systems, such as shelterwoods, have also been suggested for Norway maple management (Forest Research, 2016), though research on Norway maple in these systems is scarce. Forest managers should always consult local and regional restrictions regarding the invasiveness of Norway maple before considering management options to promote its growth.
Grasses and herbaceous weeds can compete with Norway maple (Hein et al., 2009; Savill, 2013) and sugar maple (Henry et al., 2021) regeneration. Silvicultural prescriptions that limit canopy openness or control herb and grass cover through manual or chemical weeding treatments are therefore recommended to promote Norway maple establishment in areas where this is desired (Savill, 2013).
Management with Planted Regeneration
Norway maple planting outside of urban areas is rare in both its native and introduced range (CABI, 2013; Singatullin et al., 2021). Both sugar maple management in North America and Norway maple management in Europe rely primarily on natural regeneration rather than direct seeding or planting (CABI, 2013; Godman et al., 1990; Singatullin et al., 2021), though direct sowing of Norway maple on former agricultural sites has had some success (CABI, 2019). There has been some interest in the use of Norway maple for plantations and afforestation projects in Central Europe because of its higher drought tolerance compared to the more widely planted sycamore maple (Lazic et al., 2022). Its documented status as an invasive species in other regions of the world has largely limited these applications (CABI, 2019). In North America, land managers should consider its invasive status prior to planting.
Though planting of Norway maple in nonurban forests is uncommon, it was among the most widely planted urban trees in Europe and North America (Ma et al., 2020) (see the Urban Forestry section). Norway maple is no longer recommended for planting due to its invasive potential; if Norway maple is desired, land managers should consider cultivars that do not produce viable seeds (Contreras and Hoskins, 2020). Planting recommendations using ball-and-burlap nursery stock include planting with the root flare at the soil surface, mulching, protecting transplants from trunk and root injuries, and ensuring sufficient watering (Roppolo and Miller, 2001). Mulched trees have more leaf chlorophyll, better water use efficiency, and higher leaf mineral content compared to paved trees. Soil amendments may not be necessary, as amending the backfill soil with 50 to 75 percent compost has only minor benefits, and 25 percent of compost has no effect on tree health (Ferrini and Baietto, 2007). In areas with high deer browse pressure, protection of planted seedlings and saplings may also be required (Modrý et al., 2004).
The same site treatments described in the Management with Natural Regeneration section would apply here.
Tending or Intermediate Management
The same options and considerations described in the Management with Natural Regeneration section would apply here.
Like sugar maple in North America, Norway maple responds well to regular and heavy thinning after canopy closure to maintain good growth (Horsley et al., 2002; Savill, 2013; Stone, 1986). Thinning also helps maintain mixed-species stands since Norway maple can shade out co-occurring species.
Pruning of branches to encourage good growth form during establishment improves timber quality (Forest Research, 2016). When Norway maple is used as a street tree, pruning of secondary branches to promote the growth of a single leader can help reduce the likelihood of cracking and branch failure (Gilman and Watson, 1993), which is common in the species (Tothill and Slater, 2019). Norway maple adapts to maintenance pruning well. In response to 30 percent crown pruning in mature trees, the concentration of nonstructural carbohydrates increased in unpruned branches in pruned trees (Ramirez et al., 2018). After pruning, young Norway maple branches grow faster, the leaves develop a thick spongy parenchyma, and leaf size increases (Bessonova et al., 2023), which could facilitate the replenishment of carbohydrate reserves. Heavy pruning such as topping or pollarding should be avoided because it encourages the formation of weakly attached water sprouts and reduces the heat dissipation through evaporative cooling by 81 percent (Comin et al., 2025). Pruning should be done regularly and on branches smaller than 7.5 cm (3 inches). For Norway maple, the timing of pruning does not affect wood discoloration, but wound occlusion is most likely if branches are pruned in January. In colder climates, cuts larger than 7.5 cm have less than 25 percent probability for successful occlusion within 6 years of pruning (Lund et al., 2023).
No research has been reported on the direct effects of sanitation logging on Norway maple.
No research has been reported on the direct effects of salvage logging on Norway maple.
Within the genus Acer, Norway maple is categorized in the section Platanoidea, which includes two accepted subspecies: Acer platanoides subsp. platanoides, native to temperate forests from Europe to Northern Iran, and Acer platanoides subsp. turkestanicum, found in regions extending from central Asia to northern Pakistan (Govaerts, 1995). The subspecies Acer platanoides subsp. platanoides was introduced to North America in the 1750s and has since naturalized.
The section Platanoidea contains an estimated 13 species that are morphologically characterized by their disc-shaped, flat seeds and shoots and leaves that contain milky sap. Studies including ITS and plastid markers supported a Platanoidea clade (Li et al., 2006; Suh et al., 2000). Recent studies with fossil data or molecular data (nuclear markers) (or both) support monophyly of section Platanoidea (Areces-Berazain et al., 2021; Li et al., 2019; Xia et al., 2022).
Genetic Variation
Norway maple exhibits moderate genetic variation, moderate to high heterozygosity, and distinct subpopulations across its native range in Europe and Asia, which has implications for its adaptability and invasiveness (Lazic et al., 2022). Molecular markers, primarily microsatellite markers, and allozymes, have been used to assess genetic diversity within and between populations in portions of northern Europe, Russia, Latvia, and Austria (Akhmetov et al., 2021; Eriksson et al., 2003; Lazic et al., 2022; Ruņģis and Krivmane, 2021; Rusanen et al., 2003).
There are no comprehensive studies on genetic diversity in the introduced range. A cross-continental comparison of native and invasive populations of Norway maple provided evidence that genetic differentiation was minimal in comparison to exceptional phenotypic plasticity (Gómez‐Aparicio et al., 2008).
Norway maple is likely diploid (13 haploid chromosomes), and current estimates for genome size are just under 700 Mb (Contreras and Shearer, 2018). Though it is known for its invasive role in North American forests, there is limited direct evidence of its hybridization with North American maple species (Lamarque et al., 2014).
Seed transfer guidance for Norway maple varies significantly between its native range in Europe and its invasive range in North America. In Europe, where the species is native, seed sourcing follows regional provenancing strategies designed to preserve genetic diversity and local adaptation. Guidelines regarding genetic conservation have been developed by the European Forest Genetics Resources Programme (European Forest Genetics Resources Programme, n.d.). Genetic studies in Austria have revealed moderate population differentiation, prompting the establishment of clonal seed orchards to maintain appropriate provenance integrity (Lazic et al., 2022). Moreover, broader European forestry frameworks increasingly adopt climate-adjusted provenancing, as demonstrated by Switzerland’s common garden network, which tests species resilience across varied climatic zones to inform future seed transfers (Streit et al., 2024). In contrast, Norway maple is considered invasive across much of the United States and southern Canada, where formal seed zones are neither recommended nor practiced.
Though there are examples of Norway maple exhibiting reduced seed germination, these cultivars are more often an example of only reduced fertility. By using chromosome doubling techniques, current work is focused on developing sterile triploid maples that can be propagated clonally (Contreras and Hoskins, 2020).
Genomic Resources for Forest Tree Species
Genomic studies of Norway maple have increasingly benefited from plastid and nuclear marker resources. Comparative plastome analyses have identified hypervariable regions which are effective for phylogenetic resolution and plastid marker development across the genus (Areces-Berazain et al., 2021; Yu et al., 2020). Nuclear marker development has leveraged both species-specific and cross-amplified simple sequence repeats (SSRs) (Ruņģis and Krivmane, 2021). For example, SSRs originally designed for sycamore maple, Miyabe maple (Acer miyabei), and Shantung maple (Acer truncatum) have been successfully transferred to Norway maple (Long et al., 2024; Pandey et al., 2004; Saeki et al., 2015). In addition, inter-simple sequence repeat (ISSR) markers have been generated and assessed to understand genetic structure (Akhmetov et al., 2021).
Many native moths and gall mites feed on Norway maple leaves but rarely cause severe damage (Clem and Held, 2018). Dropping of green leaves can be caused by Norway maple aphid (Periphyllus lyropictus), Norway maple seedminer (Ectoedemia sericopeza), and maple petiole miner (Caulocampus acericaulis) (table 2). Damage from flatheaded borers is common in nurseries and on drought-stressed Norway maples (LeBude and Adkins, 2014; Roppolo and Miller, 2001; Solomon, 1995). Although Norway maple is not severely affected by insect pests native to the United States (Adams et al., 2009; Cincotta et al., 2009), it is a host to the invasive Asian longhorned beetle (Anoplophora glabripennis) (Dodds and Orwig, 2011), Japanese beetle (Popillia japonica) (U.S. Department of Agriculture, 2024), spongy moth (Lymantria dispar) (Wittman and Aukema, 2019), spotted lanternfly (Lycorma delicatula) (Simisky et al., 2022), granulated ambrosia beetle (Xylosandrus crassiusculus), and black stem borer (Xylosandrus germanus) (Cavaletto et al., 2021; Russell, 2009).
Tree failure due to decay in roots and the lower stem of Norway maple caused by various fungi (e.g., Kretzschmaria deusta, Ganoderma sessile, Ganoderma applanatum, Pseudoinonotus dryadeus, and Armillaria mellea) is a major concern for urban Norway maples (fig. 7F,H). These pathogens infect trees through wounds at the tree base and in its roots (Luley, 2022). The soil-borne pathogen causing Verticillium wilt can kill Norway maples quickly (Bergdahl and Hill, 2016). Pruning cuts and stem wounds can be infected by canker pathogens which prevent wound healing (Brazee, 2025; Moorman, 2023). These unhealed wounds are infected by less aggressive decay fungi that can kill and decay branches (fig. 7D). Frost damage can expose Norway maples to Cytospora canker (Smiley et al., 1986). Foliar diseases like tar spot (Rhytisma acerinum) (fig. 7A) have primarily aesthetic impacts (Adams et al., 2009; Held et al., 2018; Stanosz and Smith, 2014). Anthracnose (caused by Aureobasidium apocryptum, Discula campestris, and Colletotrichum gleosporoides, among other pathogens) affects both leaves and twigs of Norway maple (Brazee, 2023) (fig. 7C).
Table 2—Significant insects and diseases of Norway maple, by tree structure and relative impact, with a focus on inspect pests and pathogens encountered in urban areas
| Degree of impact | Roots | Bole (bark, phloem, and xylem) | Foliage, shoots, and twigs | Flowers, fruits, and seeds |
| Greatest | Shoestring root rot (Armilliaria mellea) Ganoderma sessile—causes decay in roots and lower stem Brittle cinder (Kretzschmaria deusta)—causes decay in roots and lower stem
| Asian longhorned beetle* (Anoplophora glabripennis) Verticillium wilt (Verticillium dahliae) | Spongy moth* (Lymantria dispar) Japanese beetle* (Popillia japonica) | Japanese beetle* |
| Moderate | Mushroom root rot (Armillaria tabescens) Root rot, weeping polypore (Pseudoinonotus dryadeus) | Flatheaded appletree borer (Chrysobothris femorata) Gallmaking maple borer (Xylotrechus aceris) Mossy maze polypore (Cerrena unicolor) Cytospora canker (Valsa ambiens subsp. leucostomoides) Eutypella canker (Eutypella parasitica) Artists’ conk (Ganoderma applanatum) Target canker (Neonectria ditissima) Nectria canker (Nectria cinnabarina, Nectria galligena) Split gill fungus (Schizophyllum commune) | Whitemarked tussock moth (Orgyia leucostigma) Saddled prominent (Heterocampa guttivitta) Anthracnose (e.g., Aureobasidium apocryptum, Discula campestris, and Colletotrichum gleosporoides)
| N/A |
| Low | N/A | Spotted lanternfly* (Lycorma delicatula) Norway maple aphid* (Periphyllus lyropictus) Maple spindlegall mite (Vasates aceriscrumena) Granulated ambrosia beetle* (Xylosandrus crassiusculus) Black stem borer* (Xylosandrus germanus) Resinous polypore (Ischnoderma resinosum) Bleeding canker (Phytophthora cactorum) | Moth, leaf miner (Caloptilia packardella) Maple petiole borer, sawfly (Caulocampus acericaulis) Norway maple seedminer* (Ectoedemia sericopeza) Potato leaf hopper (Empoasca fabae) Moth, leaf miner (Phyllonorycter trinotella) Bagworm (Thyridopteryx ephemeraeformis) Powdery mildew (Sawadaia tulasnei) Tar spot* (Rhytisma acerinum) Septoria leaf spot of maple (Sphaerulina aceris) | Norway maple seedminer* |
N/A: not applicable.
Species indicated with an asterisk (*) are invasive or exotic in North America.
Figure 7—Example of (A) tar spot and (inset) early stage pycnidia. (B) Example of Septoria leafspot and (inset) pycnidia. (C) Foliar symptoms of maple anthracnose. (D) Example of a large pruning cut, which can act as an infection site for canker pathogens and decay fungi; in this photo, black mycelium of saprotrophic sooty mold fungi is visible on the bark and sapwood. (E) Example of advanced wood decay in Norway maple; this cross-section shows decay (“D”), small portions of sound but non-conducting sapwood (“SN”), and healthy sapwood (“S”). (F) Example of fruiting bodies of Kretzschmaria deusta; in this photo, the presence of this fungus indicates the advanced decay shown in the cross-section of the infected tree in panel E. (G) Example of fruiting bodies of 7 Ischnoderma resinosum on a declining and decayed tree; in this photo, the cross-section of the infected tree shown in panel E is visible. (H) Ganoderma sessile and (I) Pseudoinonotus dryadeus fruiting bodies; these are common root and stem decay fungi of urban Norway maples. Courtesy photos A and C through I by Susanna Keriö. Courtesy photo B by Yonghao Li.
Verticillium wilt can kill branches or entire trees relatively quickly. Leaf spots, anthracnose, and insect defoliators affect young trees and stressed trees more severely than healthy mature trees (Douglas, 2016; Sinclair and Lyon, 1987). Trees with cuts or wounds are more vulnerable to infection by decay fungi. Fruiting bodies of pathogenic fungi on roots or stems indicate declining tree health and decay, but the tree may still take years to die or fail (Luley, 2022).
Norway maple is a prominent landscape and street tree (Frank et al., 2013; Ma et al., 2020), and the impacts of the listed insects and pathogens are attenuated by many urban factors (Manion, 1981). Rainy springs and summers are conducive to foliar pathogens. Information is limited on how changing environmental conditions will affect Norway maple’s response to both native and exotic insect pests and pathogens in North America.
In forest environments, removal is the best response to declining Norway maples. However, to protect the health of forests and agricultural crops, it is critical that land managers know the signs associated with invasive and destructive quarantine pests such as Asian longhorned beetle or Japanese beetle on Norway maple. In urban environments, maintaining the vigor of existing trees is important (Johnson et al., 2021). Trees that have fruiting bodies of decay fungi should be monitored to avoid uncontrolled tree failure. If the site has had Verticillium wilt, Norway maples should not be planted. Raking and removing infected leaves help reduce inoculum levels of foliar pathogens. If Norway maple is to be planted and pests are a concern, cultivars that have better resistance to insects (Peterson and Smitley, 1991) and pathogens (Townsend et al., 1990) should be favored.
No published information is available describing the dominant fire regime for Norway maple as of 2024. Fires are infrequent in woodland and forested areas of the northeastern and midwestern United States, where concentrations of naturalized Norway maple are highest (Frelich et al., 2021). Fire return intervals in these regions can range from 32 to over 1,000 years (Fryer and Luensmann, 2012; Munger, 2003).
While there is no published research to date on Norway maple response to fire, Norway maple is likely a fire-sensitive species, similar to sugar maple (Kruger and Reich, 1997) and red maple (Ward and Brose, 2004). Red maple experiences high rates of postfire mortality (topkill), especially in younger and smaller individuals (1 m tall or more). Though red maple has high postfire mortality, it has an intermediate resprout rate. Postfire sprouting in red maple is greatest in individuals 2 m (6 feet) tall or more (Ward and Brose, 2004), suggesting that if Norway maple responds similarly, larger Norway maples may be more resilient to fire.
The authors found no supporting documentation for secondary interactions.
Given the presumed sensitivity to fire, prescribed burning could be a method to control Norway maple in areas where it is not desired. Biochar has been found to mitigate allelopathic impacts of Norway maple, suggesting that controlled burns could potentially control young Norway maples through the addition of charcoal (Sujeeun and Thomas, 2023). This process has been observed in boreal forests, where postfire charcoal helped reduce phenolic compounds from the dwarf shrub Empetrum hermaphroditum (Zackrisson et al., 1996). Given the potential for resprouting, the most appropriate application of prescribed fire to control Norway maple would be in the earliest stages of regeneration, when mortality is expected to be greatest and sprouting will be less prevalent. Of course, the use of fire to manage Norway maple would also have to be weighed against the potential negative impacts on any proximal fire-intolerant native species (e.g., sugar maple, American beech).
Drought regimes within Norway maple’s introduced range are classified as “random, occasional drought” in the eastern United States, “common, late summer droughts” in the midwestern United States, and “annual, seasonal droughts” in the western United States (Hanson and Weltzin, 2000). In Canada, drought patterns vary across regions. The southern prairies and interior British Columbia frequently experience droughts, whereas eastern regions like Quebec typically encounter “random, occasional droughts,” similar to the eastern United States (Canadian Climate Institute, 2025).
Across North America, droughts are predicted to increase in severity under changing environmental conditions (Vose et al., 2019). Reduced winter snowfall could also increase the likelihood of early growing season drought (Luce et al., 2016).
Norway maple is considered to have intermediate drought tolerance (Niinemets and Valladeres, 2006), though significant genetic variation in drought tolerance has been reported (Fini et al., 2009; Sjöman et al., 2015). Norway maple demonstrates isohydric behavior (Nardini et al., 2014) with stomatal control of transpiration maintaining high shoot water status to avoid hydraulic failure through cavitation, but this may cause carbon starvation during prolonged droughts (Hommel et al., 2016; Kunz et al., 2016).
Norway maple is a shallow-rooted species with most fine roots occurring in the first 0 to 10 cm (0 to 4 inches) of soil (Watson and Himelick, 1982), but roots can grow as deep as 1.5 m (5 feet) (Leuschner et al., 2024). Norway maple’s ability to increase fine root surface area in response to water scarcity (Fuchs et al., 2020; Fuchs et al. 2021) may offer it an advantage for water competition during droughts. In dense mixed plantings of 7- to 10-year-old trees, the proximity of Norway maple increased the drought mortality risk of neighboring trees, while mortality of Norway maple was not affected by drought (Hajek et al., 2022). Drops in radial growth during drought and recovery within 1 to 2 years after drought have been observed in urban sites with sealed soils (Franceschi et al., 2023; Gillner et al., 2014).
Seedlings are more impacted by drought than mature trees. Mature Norway maples have wide hydraulic safety margins and high resistance to embolism, and show only minor crown damage after severe droughts (Leuschner et al., 2024). In contrast, drought can reduce seed germination and seedling survival (Carón et al., 2015).
Drought stress can induce sooty bark disease in the closely related sycamore maple (Ogris et al., 2021), though information on its impact on Norway maple is limited (Tanney et al., 2024).
As drought increases with changing environmental conditions, Norway maple decline could pose a public safety hazard in urban areas, necessitating enhanced monitoring and preventive removals. Where retention of Norway maple canopy cover is desired, supplemental watering may be required (e.g., for street trees).
Wind is the most prevalent natural disturbance within Norway maple’s native (Brůna et al., 2013; Meyer et al., 2021) and introduced range (Martin et al., 2010; Peterson et al., 2016). Windthrow is typically associated with small gap creation (Peterson et al., 2016), but larger scale disturbances caused by more severe windstorms are within the historical range of variability (Brůna et al., 2013; Peterson et al., 2016). While shifts in wind speeds are uncertain under changing environmental conditions, occurrences of more intense storms are expected to increase (Haughian et al., 2012; Seidl et al., 2017). Ice storms can also occur within Norway maple’s native (Lafon, 2016) and introduced range (Klopčič et al., 2020). However, these disturbance events are typically low severity, at the local scale, and relatively rare compared with other disturbance events. Ice storms are predicted to increase in both frequency and intensity as environmental conditions change (Rustad and Campbell, 2012).
Deer and small mammal browse is also a common disturbance within Norway maple's native (Modrý et al., 2004) and introduced range (Martin and Marks, 2006). White-tailed deer (Odocoileus virginianus) are endemic to North America but have expanded their geographic range and increased in density drastically post-European settlement (Rooney, 2001). Norway maple also experiences insect herbivory; however, the impact and frequency of insect herbivory are greater in its native range than in its introduced range (Adams et al., 2009).
Windthrow can promote Norway maple regeneration through the creation of gaps. Norway maple has established a competitive edge in these gaps over other species, such as beech, in its native range (Meyer et al., 2021) and sugar and red maple in its introduced range owing to its fast growth rate (Martin et al., 2010). Similarly, while Norway maple is susceptible to ice damage (Klopčič et al., 2020), ice storms can cause canopy gap formation (Lafon, 2016) and promote Norway maple regeneration and growth. Extreme temperature fluctuations can cause frost cracks (Dirr, 2009), which can harbor wood-rotting fungi, especially Schizophyllum commune (French and Fuhs, 1973), or incite Cytospora canker symptoms (Smiley et al., 1986), but this issue is most common on landscape or nursery-grown trees.
Deer and other mammal browse limit Norway maple growth and spread, though the impacts of these chronic disturbances exhibit more control over Norway maple in its native range than in its introduced range (Modrý et al., 2004). In its introduced range, Norway maple exhibits a strong potential to recover by resprouting from dormant buds (Martin and Marks, 2006). Small mammal browse may have a stronger negative impact on Norway maple due to browsing at the seedling base (Martin and Marks, 2006). Similarly, insect herbivory has stronger negative impacts on Norway maple in its native range than in its introduced range (Adams et al., 2009) and Norway maple exhibits lower levels of herbivory than its native congener, sugar maple (Lapointe and Brisson, 2012) (see the Tree Growth and Stand Dynamics section).
The authors found no supporting documentation for secondary interactions.
Where management objectives are to limit Norway maple spread, managers should work to accomplish and maintain closed-canopy forests in areas with high Norway maple abundance in the midstory and understory given that canopy disturbances promote Norway maple. However, because Norway maple can also persist in dense shade, this strategy must also be coupled with active removal of Norway maple to limit its spread. In areas where forest management activities are desired, Norway maple should be controlled prior to harvest operations.
Goods
Within its native range of Europe, Norway maple wood is used for furniture, flooring, marquetry, and musical instruments (Lazic et al., 2022). It is used sparingly as a lumber species in Europe for veneer and specialty items such as tool handles, gunstocks, and violins (Nowak and Rowntree, 1990). Norway maple has an average wood density of 660 kg m-3 (41 pounds foot-3) at 15 percent moisture content, and a wavy grain (CABI, 2013).
Norway maple can be tapped for syrup, with seasonal sap yields similar to other maple species in North America but with lower sugar content (Mathews et al., 2023). Within its native range, Norway maple is also tapped for syrup and can be fermented into a beer (Svanberg et al., 2012).
Ecosystem Services
Within its native range, Norway maple contributes to tree-related microhabitats (Przepióra and Ciach, 2023). Tree-related microhabitats are structures or substrates created by living and dead trees that foster specialized species, including insects, birds, mammals, fungi, reptiles, and amphibians (Martin et al., 2022). In its native range, Norway maple supports a high number of insect galleries, nests, cracks and scars, woodpecker cavities, and cankers (Przepióra and Ciach, 2023). However, studies examining herbivores in native versus introduced ranges show that Norway maple supports fewer herbivores in introduced ranges, which is consistent with the enemy release hypothesis (Adams et al., 2009; Clem and Held, 2018). In North America, Norway maple is more often associated with reductions in biodiversity (Wyckoff and Webb, 1996) (see the Tree Growth and Stand Dynamics section).
Norway maple has a higher carbon assimilation rate than sugar maple (Kloeppel and Abrams, 1995). Carbon assimilation is a direct measure of carbon uptake and, thus, a better measure of potential atmospheric carbon dioxide reductions than carbon sequestration estimates (Fini et al., 2023). This higher assimilation rate is attributed to its higher growth rate and longer growing season (Kloeppel and Abrams, 1995). The leaf longevity of Norway maple in the eastern United States is 12 days longer than that of sugar maple (Morrison and Mauck, 2007). While carbon assimilation may be higher compared with sugar maple, Norway maple’s carbon assimilation and sequestration are considered average relative to other urban trees in its native range (Fini et al., 2023).
Carbon storage in Norway maple is moderate compared with other species. Norway maple has an oven-dry weight density of 520 kg m-3 (32 pounds feet-3), which is average for other tree species within its introduced range (McPherson et al., 2016). This is lower than sugar maple at 560 kg m-3 (35 pounds feet-3) but higher than red maple at 490 kg m-3 (31 pounds feet-3) (McPherson et al., 2016). Long-term carbon storage may also be lower in Norway maple given its relatively shorter lifespan compared with other late successional native species. The maximum age of Norway maple is only 150 years compared with sugar maple and beech, which generally live 300 to 400 years (Prentice and Helmisaari, 1991).
No research has been reported on recreational uses of Norway maple.
No research has been reported for additional ecosystem services of Norway maple.
Because Norway maple can tolerate urban conditions, it was once touted as an ideal urban tree (Bradshaw et al., 1995; Phillips, 1993). This reputation led to widespread overplanting; Norway maple is among the 10 most common street tree species in the northeastern, midwestern, and western United States (Ma et al., 2020). In the northeastern United States, 16.5 percent of street trees are Norway maple (Ma et al., 2020), and this abundance can be even higher in individual cities. For example, 37.5 percent of all street trees in Syracuse, New York, are Norway maple (Sanders, 1981). While current guidance generally tries to dissuade landowners and managers from planting Norway maple (see the Cautionary Statement), it has been planted in cities in the northeastern United States as recently as 2012 through 2017 (Doroski et al., 2020).
Naturalized populations of Norway maple are primarily found in the northeastern and midwestern United States and in parts of Ontario and Prince Edward Island (see the Distribution and Environmental Associations section). As a popular urban and landscape tree, however, it has a much broader urban range. Norway maple is the most commonly planted maple species in the Intermountain West (Hansen et al., 2021) and is also planted in suburban areas of Nova Scotia (Turner et al., 2005) and Newfoundland (Simkovic, 2020).
Forests in Cities
Norway maple is often found in urban areas, so most of the dynamics outlined in the Tree Growth and Stand Dynamics section draw from studies exploring urban forested natural areas or urban forest patches. Thus, the dynamics outlined in that section are inclusive of forests in cities; the following sections elaborate only on urban-specific information.
Norway maple dispersal is facilitated by urbanization, probably because of higher propagule pressure from historical overplanting of the species in urban areas (see Doroski et al., 2020). Roads are also a vector for Norway maple dispersal and may help facilitate its spread in urban areas (Wangen et al., 2006).
Urban soils may also promote Norway maple seedling survival. As noted in the Distribution and Environmental Associations section, high seedling survivorship has been identified in high-pH soils up to 7.5 (Martin and Marks, 2006). Urban soils are typically slightly to strongly alkaline due to fill such as concrete and cement, which release calcareous solutions into soil (Yang and Zhang, 2015). These soil types may facilitate Norway maple naturalization in urban areas.
See the Tree Growth and Stand Dynamics section for information on dynamics drawn from studies of urban forested natural areas or urban forest patches.
Trees in Planted Urban Landscapes
Planted Norway maples have an annual mortality rate of 2.1 percent in Toronto, Ontario (Steenberg et al., 2019), 6.1 percent in Baltimore, Maryland, and 8.2 percent in Cambridge, Massachusetts (Boukili et al., 2017). In all three studies, mortality rates were among the highest of all urban tree species sampled. Mean diameter growth rates range from 0.46 cm year-1 ± SD 0.23 (0.18 ± 0.09 inch year-1) (Steenberg et al., 2019) to 0.74 cm year-1 ± SE 0.05 (0.29 ± 0.02 inch year-1) (Zihang, 2023). Norway maple typically forms bark inclusions, which can weaken branch structure and result in branch failure (Tothill and Slater, 2019).
Norway maple is considered adapted to compacted soils (Simkovic, 2020), but at the time of this publication, no peer-reviewed literature specifically testing this claim was found. Some studies find that Norway maple does not grow as well in compacted soils as other common urban tree species (Kristoffersen, 2012) and that grafting success is poor in compacted soils (Howard and Oakley, 1997). Similarly, Norway maple is often promoted in urban settings for its high salt tolerance (Bassuk et al., 2009; Philips, 1993). However, empirical studies examining salt injury have found that Norway maple’s salt tolerance ranges from only moderate (Fostad and Pedersen, 2000) to low (Marosz and Nowak, 2008; Zimmerman et al., 2005) and that elevated salt levels suppress Norway maple height growth and increase leaf damage.
Norway maple is also relatively shallow rooted, which can cause issues with sidewalk heaving (Bassuk et al., 2009; Phillips, 1993).
As mentioned in the preceding sections, Norway maple has historically been valued as an urban and landscape tree. Norway maple has aesthetic value for its yellow fall foliage and the maroon leaf color of certain cultivars such as ‘Crimson King’ (Dirr, 2009). In addition to aesthetic value, this species helps mitigate the urban heat island effect, which causes temperatures in cities to be significantly higher than surrounding rural areas. While all trees provide some level of heat mitigation through the process of transpiration (Konarska et al., 2016), medium- to large-statured trees, such as Norway maple, can provide greater heat reduction through the provision of shade (Dirr, 2009; Nowak, 2021). Like all urban trees, Norway maples help slow and absorb rainfall through their leaves, branches, and roots. This ecosystem service is important in urban areas where high levels of impervious surface can lead to flooding and water quality issues. While Norway maple provides rainfall interception, the magnitude of this interception is unremarkable compared with other urban tree species (Anys and Weiler, 2023). Urban trees are often also valued for their potential to mitigate air pollution in urban areas. Though Norway maple provides some reduction of fine particles (PM2.5; 2.5 μm or smaller), it is less efficient at fine-particle removal than other common urban trees (Yang et al., 2015).
- While some research suggests Norway maple is an allelopathic species (Sujeeun and Thomas, 2023), laboratory bioassays find relatively small impacts on germination, even at high concentrations (Pisula and Meiners, 2010). Other studies find some evidence for the presence of an allelochemical but do not support the hypothesis of Norway maple having an allelopathic impact (Rich, 2004). Allelopathic impacts are notoriously hard to test (Mallik, 2008).
- The impacts of wildland fire on Norway maple are relatively unknown. This was true as of the 2003 Fire Effects Information System publication (Munger, 2003) and is still true at the time of this publication given that fire is not a primary disturbance in northeastern forests, where Norway maple is most abundant.
- There is little published research on silvicultural systems for Norway maple management in both its introduced and native range, and this paucity is unlikely to change as Norway maple is not promoted in North America through silviculture. Even within its native range, Norway maple has little silvicultural use.
- There is limited information on how changes in environmental conditions will affect the incidence of pests and diseases on Norway maple in North America. In the northeastern United States, spring rainfall is projected to increase, which may increase the severity of foliar diseases.
A.1 Management to Control
In North America, management interventions aim to remove or eradicate Norway maple rather than promoting its health and regeneration. One of the most straightforward control strategies is to cease planting Norway maple as an ornamental or street tree. While Norway maple is controlled in several States in the United States (see the Cautionary Statement), there is no Federal legislation prohibiting its use within its invasive range.
Unlike many invasive plant species that can be managed by promoting canopy closure, Norway maple is able to persist under dense shade (Martin and Marks, 2006). Therefore, strategies should focus on targeted removals. Removal of canopy and subcanopy Norway maple has been found to decrease Norway maple seedling recruitment and increase survivorship of native sugar maple seedlings (Webster et al., 2007). Sapling and pole trees can be managed with cut-stump, basal bark, and hack-and-squirt applications of systemic herbicides (e.g., glyphosate) (Webster et al., 2007). Because Norway maple is a prolific resprouter, removal alone is inadequate to control this species, and follow-up treatments may be necessary to control sprouts (Webster et al., 2007). Smaller saplings and seedlings can be hand-pulled. Webb et al. (2001) recommend episodic removal of saplings and seedlings every 2 to 3 years, given the lag time from seedling establishment to sapling recruitment. However, land managers should be cognizant of the impact that soil disturbances can have on the release of Norway maple regeneration (Webb et al., 2001).
In addition to removals, management considerations should include efforts to control potential legacy effects on soils, as changes in soils can promote Norway maple growth through positive feedbacks. Norway maple can increase nutrient concentrations (i.e., calcium, magnesium, potassium, nitrogen) and cycling rates (i.e., net nitrogen mineralization, net nitrification, calcium mineralization) (Gómez-Aparicio et al., 2008). Therefore, carbon additions to soils in the form of woodchips may be needed to help lower soil nitrogen (Afzal et al., 2023). Because Norway maple has potential allelopathic properties, biochar has also been proposed as a management strategy (Sujeeun and Thomas, 2023).
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We thank the chapter reviewers and Cynthia F. Moser for their comments and edits, which greatly improved the final chapter. We also thank Cameron Stelly, Susan Iott, Lauren Pile Knapp, and the USNAP Exotic and Invasive Species Group for their guidance throughout the development of this chapter.