Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Datasheet

Acer negundo
(box elder)

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Datasheet

Acer negundo (box elder)

Summary

  • Last modified
  • 14 November 2018
  • Datasheet Type(s)
  • Invasive Species
  • Host Plant
  • Preferred Scientific Name
  • Acer negundo
  • Preferred Common Name
  • box elder
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Plantae
  •     Phylum: Spermatophyta
  •       Subphylum: Angiospermae
  •         Class: Dicotyledonae
  • Summary of Invasiveness
  • A. negundo is a small and variable tree of little economic value native to much of North America. It has been widely planted mainly for amenity purposes in non-native parts of North America, Europe and Asia whe...

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Pictures

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PictureTitleCaptionCopyright
Unripe seeds and foliage of box-elder (A. negundo).
TitleFoliage
CaptionUnripe seeds and foliage of box-elder (A. negundo).
CopyrightPaul L. Redfearn, Jr.
Unripe seeds and foliage of box-elder (A. negundo).
FoliageUnripe seeds and foliage of box-elder (A. negundo).Paul L. Redfearn, Jr.

Identity

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Preferred Scientific Name

  • Acer negundo L.

Preferred Common Name

  • box elder

Other Scientific Names

  • Negundo aceroides Moench
  • Negundo negundo (L.) Karsten
  • Rulac fraxinifolia Adanson
  • Rulac negundo (L.) Hitchc.

International Common Names

  • English: ashleaf maple; ash-leaved maple
  • Spanish: arce; fresno de Guajuco
  • French: erable a feuilles de frene

Local Common Names

  • Canada: aulne-buis; box-elder maple; érable; érable à feuilles composées; érable à feuilles de frêne; érable à Giguère; érable à Giguère pubescent; érable argilière; érable du Manitoba; érable négundo; inland box-elder; inland Manitoba maple; plaine à giguère
  • Germany: Eschen- Ahorn; Eschenahorn
  • Iran: afraie-zinati
  • Italy: acero a foglie di frassino; acero americano
  • Netherlands: vederesdoorn
  • Poland: klon jesionolistny
  • Sweden: ask lönn
  • USA: inland boxelder; Manitoba maple; western boxelder

EPPO code

  • ACRNE (Acer negundo)

Summary of Invasiveness

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A. negundo is a small and variable tree of little economic value native to much of North America. It has been widely planted mainly for amenity purposes in non-native parts of North America, Europe and Asia where it is now regenerating freely and spreading, invading riparian zones and urban areas. In the temperate parts of the southern hemisphere the spread of A. negundo is more limited. Although this pioneer species is invasive throughout much of its introduced range, actual impacts are not great. This species has no important negative impacts on human activities. In natural habitats the species becomes an important component of the vegetation in riparian systems and increases siltation.

Taxonomic Tree

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  • Domain: Eukaryota
  •     Kingdom: Plantae
  •         Phylum: Spermatophyta
  •             Subphylum: Angiospermae
  •                 Class: Dicotyledonae
  •                     Order: Sapindales
  •                         Family: Aceraceae
  •                             Genus: Acer
  •                                 Species: Acer negundo

Notes on Taxonomy and Nomenclature

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Although A. negundo is now firmly part of the genus Acer, until relatively recently its taxonomic status has often been debated (de Jong, 1976). The differences, and its reproductive biology (e.g. dioecy) in particular, exhibited by A. negundo when compared to other species of the genus lead some taxonomists to ascribe the species to a separate genus negundo. A number of varieties has been described in its native range in North America (Rosario, 1988). These are: var. negundo L., var. interior (Britt.) Sarg., var. violaceum (Kirchn.) Jaeg., var. texanum Pax., var. californicum Sarg. and var. arizonicum Sarg. These varieties are differentiated on the basis of morphological characteristics, mainly pubescence or colour of the branches and/or samaras, and sometimes leaf shape (Anon., 1963; Rosario, 1988). Being an important ornamental tree, many cultivars exist but the variegated forms are the most commonly planted (Gelderen et al., 1994).

Description

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A. negundo is an often multi-stemmed tree reaching a height of no more than 20 m and a stem diameter of up to 1 m (Rosario, 1988). In more open vegetation the canopy usually exhibits a broad and open crown and may even become shrubby, whereas in the face of competition in a forest stand the trunk tends to be single-stemmed and straighter. Shoots are green and turn violet in the second year. The bark is grey-brown becoming dark grey and is shallowly cracked. Buds are opposite, small, 2-5 mm, two-scaled and silky white. The leaves are 15-35 cm long, pinnate with 3-5 (or 7) leaflets and light green but paler below. The leaflets are lobed and serrated. Leaflet shape is variable, for instance in var. interior the first pair of leaflets is 3-lobed. Male flowers are born in corymbs with pendent stamens whilst female flowers are in small pendent racemes. Both types of flowers are small and pale yellowish-green in colour. There is much variation in the morphology of pistillate flowers with the presence of stamens on a proportion of the flowers (Hall, 1951). The fruit consists of two fused winged samaras to 4 cm long, diverging at an angle of less than 60 degrees. The samaras separate when shed and contain a single wrinkled seed.

Plant Type

Top of page Perennial
Seed propagated
Tree
Vegetatively propagated
Woody

Distribution

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The natural distribution of A. negundo ranges from southern Canada to the mountains of Mexico and as far as Guatemala, is absent from western North America but occurs along the Atlantic coast. The various recognized varieties appear to represent fairly distinct geographic races but these often intergrade (Rosario, 1988). The range of the species has greatly expanded in North America through planting and subsequent natural regeneration and is spreading in the western USA. In Canada, although only native to the southern tip of Ontario, A. negundo is now naturalized in western provinces from Ontario to Nova Scotia (Anon., 1963). The species is widespread in urban areas throughout much of Europe following centuries of horticultural and landscape planting. It is probably more widespread in other temperate regions of the world but is absent from the tropics.

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Continent/Country/RegionDistributionLast ReportedOriginFirst ReportedInvasivePlantedReferenceNotes

Asia

ChinaPresentIntroduced Planted Cao et al., 1992
KazakhstanPresentIntroduced Planted Adamowski, 1991
TurkeyPresentIntroduced Planted Cobanoglu, 1994

North America

Canada
-AlbertaPresentNative Natural Rosario, 1988
-ManitobaPresentNative Natural Rosario, 1988
-New BrunswickPresentIntroduced Invasive Planted Rosario, 1988
-Nova ScotiaPresentIntroduced Invasive Planted
-OntarioPresentNative Natural Rosario, 1988
-Prince Edward IslandPresentIntroduced Invasive Planted Rosario, 1988
-QuebecPresentIntroduced Invasive Planted Rosario, 1988
-SaskatchewanPresentNative Natural USDA-ARS, 2003
-Yukon TerritoryPresentIntroducedBennett et al., 2010
MexicoPresentNative Natural Rosario, 1988
USA
-AlabamaPresentNative Natural Rosario, 1988
-ArizonaPresentNative Natural Rosario, 1988
-ArkansasPresentNative Natural Rosario, 1988
-CaliforniaPresentNative Natural Rosario, 1988
-ColoradoPresentNative Natural Rosario, 1988
-ConnecticutPresentNative Natural Rosario, 1988
-DelawarePresentNative Natural Rosario, 1988
-FloridaPresentNative Natural Rosario, 1988
-GeorgiaPresentNative Natural Rosario, 1988
-IdahoPresentNative Natural Rosario, 1988
-IllinoisPresentNative Natural Rosario, 1988
-IndianaPresentNative Natural Rosario, 1988
-IowaPresentNative Natural Rosario, 1988
-KansasPresentNative Natural Rosario, 1988
-KentuckyPresentNative Natural Rosario, 1988
-LouisianaPresentNative Natural Rosario, 1988
-MainePresentIntroduced Invasive Planted Rosario, 1988
-MarylandPresentNative Natural Rosario, 1988
-MassachusettsPresentNative Natural Rosario, 1988
-MichiganPresentNative Natural Rosario, 1988
-MinnesotaPresentNative Natural Rosario, 1988
-MississippiPresentNative Natural Rosario, 1988
-MissouriPresentNative Natural Rosario, 1988
-MontanaPresentNative Natural Rosario, 1988
-NebraskaPresentNative Natural Rosario, 1988
-NevadaPresentNative Natural Rosario, 1988
-New HampshirePresentNative Natural Rosario, 1988
-New JerseyPresentNative Natural Rosario, 1988
-New MexicoPresentNative Natural Rosario, 1988
-New YorkPresentNative Natural Rosario, 1988
-North CarolinaPresentNative Natural Rosario, 1988
-North DakotaPresentNative Natural Rosario, 1988
-OhioPresentNative Natural Rosario, 1988
-OklahomaPresentNative Natural USDA-ARS, 2003
-OregonPresentIntroduced Invasive Planted Rosario, 1988
-PennsylvaniaPresentNative Natural Rosario, 1988
-South CarolinaPresentNative Natural Rosario, 1988
-South DakotaPresentNative Natural Rosario, 1988
-TennesseePresentNative Natural Rosario, 1988
-TexasPresentNative Natural Rosario, 1988
-UtahPresentNative Natural Rosario, 1988
-VermontPresentNative Natural USDA-ARS, 2003
-VirginiaPresentNative Natural Rosario, 1988
-WashingtonPresentIntroduced Invasive Planted Rosario, 1988
-West VirginiaPresentNative Natural Rosario, 1988
-WisconsinPresentNative Natural Rosario, 1988
-WyomingPresentNative Natural Rosario, 1988

Central America and Caribbean

GuatemalaPresentNative Natural Rosario, 1988

South America

ArgentinaRestricted distributionIntroduced Planted Simberloff et al., 2002

Europe

AustriaRestricted distributionIntroduced Invasive Planted Drescher and Magnes, 2002
BulgariaPresentIntroduced Planted Tutin et al., 1968
Czech RepublicRestricted distributionIntroduced1835 Invasive Pysek et al., 2002; Pysek and Prach, 2003
FrancePresentIntroduced Invasive Planted Aboucaya, 1999
GermanyRestricted distributionIntroduced1736 Invasive Sachse, 1991; Kowarik, 1992
HungaryRestricted distributionIntroduced Invasive Planted Török et al., 2003
ItalyPresentIntroduced Planted Antonaroli, 1998
PolandRestricted distributionIntroduced1800 Invasive Zajac et al., 1998; Medrzycki and Pabjanek, 2001
Russian Federation
-Central RussiaRestricted distributionIntroduced Planted Adamowski, 1991
-Northern RussiaRestricted distributionIntroduced Planted Adamowski, 1991
-Russian Far EastRestricted distributionIntroduced Planted Adamowski, 1991
-Southern RussiaRestricted distributionIntroduced Planted Adamowski, 1991
-Western SiberiaRestricted distributionIntroducedbefore 1940 Invasive Planted Adamowski, 1991
SlovakiaPresentIntroduced1699Tutin et al., 1968; Lohmeyer and Sukopp, 1992
SpainPresentIntroduced Planted Tutin et al., 1968
SwedenRestricted distributionIntroduced Invasive Planted Stöcklin et al., 2003
SwitzerlandPresentIntroduced Planted Tutin et al., 1968
UKRestricted distributionIntroduced1688 Not invasive Planted Clement and Foster, 1994
UkraineRestricted distributionIntroduced Invasive Planted Mosyakin and Yavorska, 2002

Oceania

Australia
-New South WalesRestricted distributionIntroduced Invasive Planted Howell and Benson, 2000
-QueenslandPresentIntroduced Planted Groves and Hosking, 1997
-VictoriaPresentIntroduced Invasive Planted Groves and Hosking, 1997
New ZealandPresentIntroduced Invasive Planted Webb et al., 1988

History of Introduction and Spread

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A. negundo was introduced to the UK in 1688. It was then planted throughout much of Europe but the history of introduction and spread through the continent is fragmentary. It was reported as spreading in Slovakia in 1699 (Lohmeyer and Sukopp, 1992). Pysek and Prach (2003) stated that it was first introduced to the region now known as the Czech Republic in 1835 and first recorded in the wild in 1875. It reached the Brandenburg region of Germany in 1736 (Kowarik, 1992) and the first record in the wild was in 1919, hence a time-lag of 183 years between the species introduction and its spread. In Berlin, the tree was only observed to spread in 1945 (Kowarik, 1992). It was thought to have been introduced to Poland around 1800 (Zajac et al., 1998). In Siberia, A. negundo has been cultivated since at least the 1940s and was planted in the Novosibirsk Botanical Garden in 1954 (Adamowski, 1991). In Australia and New Zealand the spread of A. negundo is recent; for example, in Australia it was only recorded as naturally regenerating in 1987 (Groves and Hosking, 1997; Williams et al., 2002).

Risk of Introduction

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In Australia, a native alternative to A. negundo is being promoted and more species are to be identified by the horticultural trade (Lewis and Stephens, 2001). In New Zealand, as part of a Conservation Weed Risk assessment it has gained a relatively high score but experts have ranked the species as a minor weed because it has yet to become a conservation weed (Williams et al., 2002).

Habitat

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A. negundo is widespread in riparian and palustrine plant communities and has been reported from a variety of vegetation types in the USA (Rosario, 1988). It is most commonly associated with deciduous forest communities but also occurs in scrub- and grass-dominated vegetation types. In continental Europe it is now common in many urban areas and along many river systems (Sachse, 1991) and in Toronto, Canada it is reported as invading all habitat types (Havinga, 2000). In Europe, A. negundo is invading ecosystems that are now rare and protected such as virgin forest, e.g. Bialowieza in Poland (Adamowski et al., 2002) and riparian reserves (Drescher and Magnes, 2002).

Habitat List

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CategorySub-CategoryHabitatPresenceStatus
Terrestrial
 
Terrestrial – ManagedRail / roadsides Present, no further details Harmful (pest or invasive)
Urban / peri-urban areas Present, no further details Harmful (pest or invasive)
Terrestrial ‑ Natural / Semi-naturalNatural forests Present, no further details Harmful (pest or invasive)

Hosts/Species Affected

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Some abandoned pastures, for instance in Poland, are readily colonized by A. negundo (Falinski, 1998). It is an occasional invader of cropland and forested areas including plantations.

Biology and Ecology

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Genetics

The chromosome number is 2n=26 (Foster, 1933). The sex expression of this dioecious species is believed to be genetically controlled and therefore no sex switching occurs (Dawson and Geber, 1999).

Physiology and Phenology

A. negundo is a fast growing and relatively short lived species with a maximum life span of 100 years but more typically of about 75 years. Sexual dimorphism in A. negundo has long been noticed. Lysova and Khiznyak (1976) reported greater height and stem diameter in male compared to female individuals and Ramp and Stephenson (1983) found that males produced more leaf biomass and females more radial growth. Willson (1986) reported that fruit production had no detectable effect on shoot extension growth of female trees compared to male individuals. Fruiting branches grew less than asexual branches in one year out of two but the degree of incremental growth reduction was independent of fecundity levels. These studies indicated that genders responded differently to water availability leading to a segregation of genders (Dawson and Ehleringer, 1993). However, Ward et al. (2002) demonstrated this was true of wet years, with female individuals exhibiting higher growth rate and being more profligate water users, whereas in dry years both sexes showed similar growth and physiological responses. Increasing precipitation would thus favour female trees and also alter the water flux from riparian ecosystems. Flowers of both male and female trees usually appear in spring well before the leaves. The fruits often persist on the tree well into the winter. In North America, large seed crops are produced annually.

Reproductive Biology

Unlike other species of maples which are all hermaphroditic with a wide array of sex expression, A. negundo is a dioecious species (de Jong, 1976). The sex ratio is variable and often skewed towards males especially on drier ground away from streamsides (Lysova and Khiznyak, 1976; Sachse, 1992; Ward et al., 2002). The tree may start bearing fruit when it is just 5 years old (Sachse, 1992). There are approximately 30,000 seed/kg (Olson and Gabriel, 1974). The tree is both wind-pollinated and wind-dispersed, although dispersal by birds and squirrels also occurs. Vegetative reproduction is common on damaged individuals. Exposed or damaged roots will produce new shoots. Shelterbelt trees whose bole had died as a result of drought have been known to recover by producing root sprouts (Rosario, 1988). Germination under test conditions varies widely from 0 to 96% (Williams and Winstead, 1972; Olson and Gabriel, 1974). In the USA, Williams and Winstead (1972) found that northern populations required shorter stratification periods, germinated at colder temperatures and with a higher germination rate than southern populations. Under natural conditions it regenerates readily on disturbed and moist soils and does tolerate medium shade (Rosario, 1988) but poor establishment or high seedling mortality occurs in dense ground cover or under closed canopy (Sachse, 1992).

Environmental Requirements

A. negundo is generally a temperate species tolerant of a wide range of environmental conditions. It is tolerant to water logging (Howell and Benson, 2000) and is highly sensitive to water stress (Ward et al., 2002), but it is also recognized as a drought-tolerant tree once established (Rosario, 1988). Dawson and Ehleringer (1991) have shown that juveniles depend solely on precipitation or stream water for approximately the first ten years, whereas older trees rely on groundwater. Although often classified as pioneer species (Tickner et al., 2001) it is moderately shade-tolerant (Niinemets, 1998). This fast-growing species is hardy and is resistant to cold (Rosario, 1988). In North America, its upper and lower altitudinal range varies greatly ranging from 680 to 3048 m with a range no greater than 1800 m and usually less than 500 m in any one state (Rosario, 1988). Branches readily break during stormy weather and being thin-barked, trees are readily injured by fire (Rosario, 1988).

Associations

As A. negundo favours disturbed ground and higher light intensities it becomes established in the earlier stages of succession.

Latitude/Altitude Ranges

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Latitude North (°N)Latitude South (°S)Altitude Lower (m)Altitude Upper (m)
54 15 0 3050

Air Temperature

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Parameter Lower limit Upper limit
Absolute minimum temperature (ºC) 0 0
Mean annual temperature (ºC) 0 22
Mean maximum temperature of hottest month (ºC) 0 0
Mean minimum temperature of coldest month (ºC) 0 0

Rainfall

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ParameterLower limitUpper limitDescription
Dry season duration04number of consecutive months with <40 mm rainfall
Mean annual rainfall4002000mm; lower/upper limits

Soil Tolerances

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Soil drainage

  • free
  • impeded
  • seasonally waterlogged

Soil reaction

  • acid
  • neutral

Soil texture

  • heavy
  • light
  • medium

Notes on Natural Enemies

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A number of insect pests or fungal diseases have been noted on A. negundo (e.g. Gilman and Watson, 1993) but few have been reported to adversely affect the species. It is susceptible to heartrot and some insect pests but these rarely kill it. The boxelder bug, Boisea trivittata (Say) feeds primarily on seed-bearing trees by sucking sap from the leaves, tender twigs and developing fruits, and although they cause little damage they are a nuisance in dwellings (Vail et al., 2002).

Means of Movement and Dispersal

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Natural Dispersal (Non-Biotic)

A. negundo, like all other maple species, is chiefly wind-dispersed. Dispersal in maples is usually localized, no more than 100 m from the seed source, but may occasionally be spread over several kilometres if seeds are released when hard snow lies on the ground and very windy weather prevails (Binggeli, 1992). In riparian systems, samaras are probably also dispersed by water but the importance of this dispersal mechanism is unclear.

Vector Transmission (Biotic)

Limited dispersal by birds and squirrels may occur.

Agricultural Practices

In several parts of the world the tree has been extensively planted in hedges and as a windbreak. The current importance of this practice, and in its introduced range in particular, is unknown.

Accidental Introduction

There is a low risk of accidental introductions.

Intentional Introduction

Because A. negundo is an important ornamental tree species with a number of varieties, nearly all new introductions will be intentional. Even where already present the introduction of new varieties/ecotypes may result in the establishment of weedy strains.

Pathway Vectors

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VectorNotesLong DistanceLocalReferences
Soil, sand and gravel Yes

Plant Trade

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Plant parts liable to carry the pest in trade/transportPest stagesBorne internallyBorne externallyVisibility of pest or symptoms
Fruits (inc. pods) fruits
True seeds (inc. grain) seeds

Impact Summary

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CategoryImpact
Animal/plant collections None
Animal/plant products None
Biodiversity (generally) Negative
Crop production Negative
Fisheries / aquaculture None
Forestry production Negative
Human health None
Livestock production None
Native fauna None
Rare/protected species None
Tourism None
Trade/international relations None
Transport/travel None

Impact

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No relevant instances are documented, but it has been reported that the tree may be poisonous to livestock (Rosario, 1988).

Environmental Impact

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Sediment deposition in an A. negundo stand was found to be greater than in native vegetation after a major flood event (8.4 ± 0.4 kg/m² vs 5.8 ± 0.7 kg/m²) (Brunet and Astin, 1997). Other effects of A. negundo on the environment have not been quantified.

Impact: Biodiversity

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No relevant instances are documented. As it becomes a major component of the ecology of European riparian vegetation, its presence will probably result in a shift in species composition reducing the presence of some species. For instance, in France A. negundo is now an important component of the Loire Valley vegetation but its impact on the populations of the re-introduced European beaver is unknown (Fustec et al., 2001).

Social Impact

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This species does not to have deleterious attributes such as spines or health-inducing risks and as such probably has limited social impacts. However, in the USA the insect Boisea trivittata (Say), after feeding on pistillate trees, over-winters on or near buildings. In spring, when it starts disperse to breed, this largish insect (over 1 cm long), may enter houses in large numbers and stain walls and curtains with brown faecal material. When crushed they produce a foul odour and may bite if handled carelessly (Vail et al., 2002). This harmful social impact has yet to be reported from Europe and other regions where the species has been introduced.

Risk and Impact Factors

Top of page Invasiveness
  • Proved invasive outside its native range
  • Highly adaptable to different environments
  • Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
  • Has high reproductive potential
Impact outcomes
  • Damaged ecosystem services
  • Ecosystem change/ habitat alteration
Likelihood of entry/control
  • Highly likely to be transported internationally deliberately

Uses

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Little economic use is made of this species as its timber has undesirable characteristics, being light, soft, close grained and of low strength. Locally, the wood may be used to make boxes and in rough construction, but it is only occasionally used to produce cheap furniture and other wooden products. Formerly, the wood was used for posts, fencing and fuel. However, it is a poor fuel as the wood is soft and spongy (Rosario, 1988). In North America, the foliage of A. negundo has poor nutritional value for livestock. It is a browse species of secondary importance to deer whereas the seeds are an important food source for birds and squirrels. It has a good value as cover for both wildlife and livestock and has been used to revegetate riparian areas (Rosario, 1988).

Uses List

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Environmental

  • Revegetation
  • Shade and shelter

General

  • Ornamental

Materials

  • Wood/timber

Wood Products

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Containers

  • Boxes

Roundwood

  • Posts
  • Roundwood structures

Similarities to Other Species/Conditions

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If no fruiting material is observable, the species, because of its mainly pinnate foliage, could be readily ascribed to a genus other than Acer. However, when present, the distinct samaras clearly indicate that the species belongs to the maple (Aceraceae) family.

Prevention and Control

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To date, little effort has been undertaken to control this species although its control has been advocated, for instance in Austria (Drescher and Magnes, 2002). No information is available for cultural, chemical or mechanical control although cutting and stump treatments used on other tree species may prove effective. A. negundo has not been considered for biological control though numerous insect pests are recorded on the species. The use of male trees only in amenity planting would eliminate risks of spread in the introduced range.

References

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Aboucaya A, 1999. Flore exotique et invasions végétales sur les berges du Rhône. La Garance Voyageuse. 48:35-40.

Adamowski W, 1991. Naturalization of Acer negundo in the environs of Novosibirsk (West Siberia). Phytocoenosis, 3:41-42.

Adamowski W; Dvorak L; Ramanjuk I, 2002. Atlas of alien woody species of the Bialowieza Primaeval Forest. Phytocoenosis, 14:1-304.

Anon., 1963. Native trees of Canada. Bulletin No. 61. Ottawa, Canada: Department of Forestry.

Antonaroli R, 1998. Vegetation census in Sassuolo comune: preliminary results. Genio Rurale, 61(9):36-40.

Bennett BA; Catling PM; Cody WJ; Argus G, 2010. New records of vascular plants in the Yukon Territory VIII. Canadian Field-Naturalist, 124(1):1-27. http://www.ofnc.ca/cfn/124-1/Bennett_etal.pdf

Binggeli P, 1992. Patterns of invasion of sycamore (Acer pseudoplatanus L.) in relation to species and ecosystem attributes. DPhil Thesis. Belfast, UK: University of Ulster.

Brunet R-C; Astin KB, 1997. Spatio-temporal variations in sediment nutrient levels: the River Adour. Landscape Ecology, 12:171-184.

Cao W; Zhuo LH; Huang PH; Li GF, 1992. Pollen morphology and its taxonomic significance for Acer Linn. from NE China. Bulletin of Botanical Research, 12(3):309-315.

Clement EJ; Foster MC, 1994. Alien plants of the British Isles: a provisional catalogue of vascular plants (excluding grasses). Oundle, UK; Botanical Society of the British Isles, 590 pp.

Cobanoglu S, 1994. A new species of Eulecanium Ckll. (Homoptera: Coccidae) for the fauna of Turkey. Doga, Turk Tarm ve Ormanclk Dergisi, 17(4):997-1003

Dawson TE; Ehleringer JR, 1991. Streamside trees that do not use streamwater. Nature, 350:335-337.

Dawson TE; Ehleringer JR, 1993. Gender-specific physiology, carbon isotope discrimination, and habitat distribution in boxelder, Acer negundo. Ecology, 74:798-815.

Dawson TE; Geber MA, 1999. Sexual dimorphism in physiology and morphology. In: Geber MA, Dawson TE, Delph LF, eds. Gender and Sexual Dimorphism in Flowering Plants. Springer-Verlag, Berlin, 175-215.

Drescher A; Magnes M, 2002. Anthropochoren im Nationalpark Donau-Auen - Ziel von Bekämpfungsmaßnahmen oder Bereicherung der Biodiversität? Osterreichisches Botanikertreffen. Bundesanstalt für alpenländische Landwirtschaft Gumpenstein, Irdning, Germany, 141-144.

Falinski JB, 1998. Invasive alien plants, vegetation dynamics and neophytism. In: Falinski JB, Adamowski W, Jackowiak B, eds. Synathopization of plant cover in new Polish research. Phytocoenosis, 10:163-187.

Foster RC, 1933. Chromosome numbers in Acer and Staphylea. Journal of the Arnold Arboretum, 14:386-393.

Fustec J; Lode T; Jacques D Le; Cormier JP, 2001. Colonization, riparian habitat selection and home range size in a reintroduced population of European beavers in the Loire. Freshwater Biology, 46:1361-1371.

Gelderen DM van; Jong PC de; Oterdoom HJ, 1994. Maples of the world. Portland, Oregon, USA; Timber Press, 458 pp.

Gilman EF; Watson DG, 1993. Acer negundo - Boxelder. University of Florida Fact Sheet ST-20. Environmental Horticulture Department, Florida Cooperative Extension Service, USA:Institute of Food and Agricultural Sciences.

Groves RH; Hosking JR, 1997. Recent incursions of weeds to Australia 1971-1995. Technical Series No. 38. Adelaide, Australia: CRC for Weed Management Systems.

Hall BA, 1951. The floral anatomy of the genus Acer. American Journal of Botany, 38:793-799.

Havinga D, 2000. Sustaining biodiversity - A strategic plan for managing invasive plants in Southern Ontario. Ontario, Toronto: City of Toronto and Society for Ecological Restoration. http://www.serontario.org/pdfs/exotics.pdf.

Howell J; Benson D, 2000. Predicting potential impacts of environmental flows on weedy riparian vegetation of the Hawkesbury-Nepean River, south-eastern Australia. Austral Ecology, 25(5):463-475.

Jong PC de, 1976. Flowering and sex expression in Acer L. Mededelingen van de Landbouwhoogeschool te Wageningen, 76:1-201.

Kowarik I, 1992. Einführung und Ausbreitung nichteinheimischer Gehölzarten in Berlin und Brandenburg und ihre Folgen für Flora und Vegetation. Ein Modell fur die Freitsetzun gentechnisch veranderter Organismen. Verhandlung des Botanischen Vereins von Berlin und Brandenburg, 3:1-188.

Lewis P; Stephens R, 2001. Discovering alternatives to garden escapes. The Nursery Papers, 2001/12:1-4.

Lohmeyer W; Sukopp H, 1992. Agriophyten in der Vegetation Mitteleuropas. Schriftenreihe für Vegetationskunde, 25:1-213.

Lysova NV; Khiznyak NI, 1976. Sex differences in trees in the dry steppe. Soviet Journal of Ecology, 6:522-527.

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