Invasion Biology Introduced Species Summary Project

Introduced Species Summary Project
Norway maple (Acer platanoides)

Common Name: Norway maple

Scientific Name: Acer platanoides

Classification:

Kingdom: Plantae

Subkingdom: Tracheobionta

Superdivision: Spermatophyta

Division: Magnoliophyta

Class: Magnoliopsida
Subclass: Rosidae

Order: Sapindales
Family: Aceraceae

Identification: The Norway maple is a large deciduous canopy tree that can grow up to 90 feet. It has a

broad, rounded crown that is densely limbed. The bark begins smooth and grayish, but later becomes darker and narrowly and vertically fissured. The leaves are opposite and can be very large, up to 7” both long and wide and are palmately veined and notched with 5 distinct lobes. The top surface is a dull green, and the underside is hairless, glossy and pale. They turn bright yellow in autumn. The leaf stalk is long and narrow and produces a milky sap when broken at the end. Flowers are bright green, 5/16” wide, with 5 upright petals clusters which occur just before leaf out. Fruit is 2 “helicopter blades”, or samaras, each about 1-2” long that contain a seed in the middle. The samaras mature by the end of summer and are dispersed by the wind. It is possible that some seeds are eaten and dispersed by birds and small mammals as well. Buds are very large, much larger than the buds of sugar and red maples ( Acer saccharum & Acer rubrum ). They are glabrous,

stocky and usually turn green to red with large scales surrounding. The terminal bud is especially large and is an easy indentifier from native maples in the winter (but not to be confused with the sycamore maple, Acer psuedoplatanus, another invasive species, which has a large terminal bud that remains green).

Acer is the name for maples within the family Aceraceae and platanoides means “like platanus”, or like the sycamore because its leaves resemble that tree. It is, however, not related to it.

Original Distribution: The Norway maple is native to most of Europe and Asia Minor. Its range sweeps from Norway southeast to the Caucasus and northern Turkey.

Current Distribution: In addition to its native range, the Norway maple is widely planted in the United States as an ornamental yard and street shade tree. Currently it is found in 24 states and is considered invasive in most of them. Its highest concentration is found in the mid-Atlantic states through New England and is found in every state along the eastern seaboard from North Carolina to Maine. Its range has expanded westward to the upper mid-west from Ohio to Minnesota and to the south-central states of Kentucky and Tennessee. It has also been widely planted in towns in the western states of Washington and Idaho.

Site and Date of Introduction: The Norway maple was first introduced to North America between 1750 and 1760 as an ornamental shade tree in the northeastern United States. It was brought to the Pacific Northwest in the 1870s.

Mode(s) of Introduction: It reached the East Coast, and later the West Coast by ship sailing from Europe or perhaps from Britain where it was also introduced from mainland Europe. Currently it is offered for cultivation in nurseries throughout the country, including the New York State Nursery, despite its status in that state by the NYS Natural Heritage Program as one of its “top twenty” invasive plants.

Reason(s) Why it has Become Established: The Norway maple reproduces quite freely and its large samaras travel easily over the wind both locally and to new areas. The seeds germinate quickly. It is a very hardy, fast-growing tree and is very tolerant of the harsh conditions of city dust, car exhaust and industrial smoke. Thus its place as a city shade tree has become well-known and it has been planted vigorously for over two hundred years. Today it is one of the most common street trees in the United States. It can occur on eroded hill sides and along broken sidewalks as its tolerance for nutrient-poor soil is great. It is also shade tolerant and thrives well in dark mature forest understories. Also it leafs out before most other species do and goes to leaf off later, prolonging its growing season considerably.

All of these factors have led up to the Norway maple easily escaping cultivation and spreading out into fields, edge habitats, disrupted habitats, and mature forests. It quickly shades out other tree, shrub and herbaceous species and establishes itself as the primary canopy cover. Since its seedlings and saplings grow well in the shade of the bigger seed-source tree, it forms monotypic stands that perpetually expand.

Ecological Role: The Norway maple is predominately a shade tree, and even in a dense canopy

tends to retain a relatively expansive crown. As a pioneer species, Norway maples can create shade

in its natural habitat for shade tolerant second-succession conifers, such as hemlocks. Also, as mentioned, its seeds can be eaten by birds and small mammals. In lean acorn years, squirrels and porcupines might also strip away the bark to gnaw on the cambium layer (provided there are no sugar or red maples nearby, both of which provide a tastier and more copious sap).

Benefit(s): The Norway maple seems to offer little commercial benefit other than firewood. As a strong fairer in unhealthy soils, it creates important root structures on nutrient poor soils found on steep slopes that would otherwise be prone to erosion. Its primary function in cultivation has been as an ornamental shade tree. It is very tolerant of temperature extremes and so performs well in open, hot areas such as lawns, municipal parks and along streets. They grow quickly and without much care so one can occupy a newly landscaped area as a large tree in little time. They also provide an aesthetic function in towns and cities as they turn bright yellow in autumn.

Threat(s): The greatest threat the Norway maple presents to North America is ultimately the domination of forest canopy and the subsequent loss of richness of native species, both in the canopy and understories. Because of its hardiness, ability to grow in a variety of soils, rapid growth, and copious seed production the Norway maple long ago spread into the mature and second-growth forests of the northeast U.S. In doing so, in many areas it has outcompeted native canopy species such as red oak (Quercus rubus), pin oak (Quercus palustris), tulip tree (Liriodendron tulipifera), red maple (Acer rubrum) and bitternut hickory (Carya cordiformis). Because it creates large amounts of shade it has inhibited the growth of mid-layer species such as hackberry (Celtis occidentalis), flowering dogwood (Cornus florida), redbud (Cercis canadensis) and black cherry (Prunus serotina).

Once it has established itself as the dominant canopy species, the Norway maple works to both vigorously propagate its own seedlings and shade out other species seedlings. In a study done by Peter Wyckoff and Sara Webb of Drew University, it was determined that even the sugar maple (Acer saccharum) and American beech (Fagus grandifolia), which are the only two canopy species in the northeast U.S. that are not shaded out by the Norway maple as they reach for the canopy, did not fair well as seedlings under a Norway maple canopy. Yet under the same canopy Norway maple seedlings comprised up to 98% of all seedlings found. Therefore, the Norway maple monotypic culture not only spreads quickly, but is established quickly.

The Norway maple is also a primary host to the Asian longhorn beetle (Anoplophora glabripennis). This is a large insect that lays its eggs within the bark of the tree. The larvae then tunnel into the wood and create extensive galleries within the heartwood and cambium. This creates great damage to the trees’

structure and nutrient flow. Adults then chew their way out to infest other nearby trees. The Asian longhorn beetle is fast becoming a danger to eastern hardwood forests.

The steady take-over of many natural forests in the U.S., and most importantly in the northeastern U.S., by the Norway maple will continue until major seed source mature trees are eliminated followed by the elimination of as many saplings and seedlings as possible. Unfortunately, this is a monumental task of

almost impossible proportions since the tree has become so abundant in natural areas already. The continued planting of the tree, both on private and public lands, and the continued offering of it from nurseries in the U.S. only exacerbates the problem and helps in the demise of native American forests.

Control Level Diagnosis: The control of the Norway maple is of the highest priority. Complete eradication seems unlikely but immediate control will at least slow its rapid spread and give forests that are already infested with it a chance to recover while there are still other species present in those forests to help in such an effort.

Control Method: Methods of removing or halting the growth of the Norway maple vary and can be determined by the severity of the infestation, the type of environment they are found in, and resources available. Preventative control should also not be overlooked for land managers seeking to plant large, hardy, shade-bearing trees.

If many Norway maples are already established in an area and have begun to compose all or some of the canopy, it is important that the large seed-source trees are removed first. If natural resource management of the area is long-term, then pruning large Norway maples may be the best option. In doing so more of the forest structure is allowed to remain while slowly eliminating seed-bearing limbs, eventually leaving a standing dead tree available for habitation by natural residents of the forest such as woodpeckers, insects and rodents.

However, if the same stand of Norway maples is managed on a short-term basis, then tree removal might be the best solution. If large trees are removed, however, it is very important that native plants are available to plant so sun-loving invasive vines do not take over the space beneath the newly opened canopy. Girdling large trees by cutting into the cambium layer around the trunk in a continuous ring is effective in killing them, typically within a couple of growing seasons. This also allows for more the forest structure to remain and prevents an immediate hole in the canopy.

Herbicides are effective in speeding up the killing process by applying to both cut stumps and girdled trees. Tryclopyrs and glyphosate agents are readily available and effective. Basel bark treatments can also be used and have proven to be effective in killing large Norway maples by the Natural Resources

Group of the New York City Parks Department. This method also keeps the dead tree in place.

If only seedlings and saplings require removing, hand weeding may be the only process needed. A weed wrench, which is a long-handled device that grips a sapling at its base, uses leverage to pull Norway maples out of the ground with most of their roots intact. Small saplings can also be snipped using pruning loppers or machetes and followed by applying herbicide to the exposed stump.

Finally, the best thing landscapers and developers can do in this effort is: do not plant Norway maples! Native alternatives are available that provide as much shade and aesthetic presence as the Norway maple. Some of these are: red maple, sweet gum (Liquidamber styraciflua), black gum (Nyssa sylvatica), and willow oak (Quercus phellos).

References:

Gargiullo, Dr. Margaret B., Plants of New York City Natural Areas, NYC Parks, Natural Resources Group, 2002

Little, Elbert L. , The Audubon Society Field Guide to North American Trees, Alfred A. Knopf, New York, 1980

Swearingen, J.,K. Reshetiloff, B. Slattery, S. Zwicker, Plant Invaders of Mid-Atlantic Natural Areas, National Park Service/ U.S. Fish and Wildlife Service, 2002

Webb, Sara L., T.H. Pendergast IV, M.E. Dwyer, “ Response of native and exotic maple seedlings banks to removal of the exotic, invasive Norway maple (Acer platanoides)”, Journal of the Torrey Botanical Society, 128(2), 2001, pp. 141-149

Wyckoff, Peter H., Sara L. Webb, “ Understory influence of the invasive Norway maple (Acer platanoides)”, Bulletin of the Torrey Botanical Club, 123(3), 1996, pp. 197-205

http://oregonstate.edu/dept/ldplants/acplg.htm

http://www.ipcnys.org/ipc_twentyap.html

http://plants.usda.gov/cgi_bin/topics.cgi

http://www.dsisd.k12.mi.us/mff/TreeBasics/TreeIDspplist.htm

Forestry team of the Natural Resources Group, NYC Parks Department, New York, NY

Natural Resources team, Prospect Park, Brooklyn, NY

Photo from: http://oregonstate.edu/dept/ldplants/acpl1.htm

Author: Rich Love
Last Edited: February 17, 2003

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