Common Name: Tree of heaven, Chinese sumac, stinking sumac, varnish treeAuthor: Patricia J. Wynne
Scientific Name: Ailanthus altissima
Classification:Phylum or Division: Magnoliophyta
Identification: Ailanthus altissima is the only species introduced into North America of the Quassia family, which includes five native trees and two native shrubs. It is a large deciduous tree that grows up to 80 feet rapidly from a straight, gray trunk. The leaves are pinnately compound, with up to 41 leaflets spaced alternately on the one-to-four-foot leaf veins (see illustration). At the base of each leaflet are one or two teeth. Green above and silvery below, the leaflets are fuzzy when young; oil glands at the base produce a foul smell when the leaves are crushed. Seedpods are reddish brown, produced in late summer. Each is between 1 ½ to 2 ½ inches long and twisted like a propeller, each with one seed. Bark is gray, smooth to bumpy and it becomes fissured with age. Like the leaves it is hairy when the tree is young. Trees are unisexual and bisexual with small, half-inch five-petaled yellow-green flowers in dense terminal clusters. Male flowers have a disagreeable odor, which has led to one of the plant’s common names, stinking sumac. Twigs are also hairy and produce a round, wide, open crown. Both the bark and wood contain astringent chemicals.
Original Distribution: Northern and central China
Current Distribution: In the United States, 41 continuguous continental states, except Minnesota, Montana, New Hampshire, North Dakota, South Dakota Vermont, and Wyoming, as well as Hawaii.
Site and Date of Introduction: Introduced into Philadelphia, Pennsylvania, by William Hamilton in 1784 for his garden. On the West coast it was also introduced for medicinal purposes by Chinese immigrants in the Gold Rush of the 1850's.
Mode(s) of Introduction: Hamilton brought a specimen from England by ship for ornamental purposes; the Chinese also brought their samples with them by ship.
Reason(s) Why it has Become Established: A. altissima is a "classic weed" species (Stobel, 1991): It reproduces at a rate of 325,000 seeds per tree per year. Its winged seeds disperse easily, often taking advantage of the wind-tunnel effect of roadways, but the plant also spreads by aggressive suckers, or runners. The root system can push into cracks in sidewalks and building foundations (see photo). It can establish itself in the poorest of ecological environments. This capacity led to its becoming a metaphor for the resilience of poor families in large cities, as expressed in A Tree Grows in Brooklyn by Betty Smith. Not only does it grow in the poorest soils, but it also tolerates air pollution well.
The tree of heaven grows swiftly to become a large tree, growing four feet per year and blocking the light for native species beneath it. In addition, its leaves are toxic to over 40 native species of plants, and it is unpalatable to herbivores. Ailanthus can overwinter in northern climates, and is resistant to both frost and drought, giving it a clear competitive edge over native species.
Because of these attributes, A. altissima has been dubbed the "tree of hell" by Pennsylvania state botanists.
Ailanthus penetrating building foundation City block invaded by Ailanthus
Ecological Role: A. altissima prevents erosion, and it provides shade and roosts for nesting birds. As a pioneer species, it grows in environments where other species of plants cannot.
Benefit(s): The tree of heaven is believed to have medicinal value in Asian traditional medicine as a remedy for asthma, worm infestation, vaginal discharge, diarrhea, and mentrual cramps. In Africa, it is used as a treatment for heart problems, seizures, and menstrual discomfort. In France, the leaves of the tree of heaven are used instead of mulberry leaves for feeding silkworm moths. The wood of A. altissima may be used in crafts and woodworking. The toxin produced in the leaves, bark, and wood is currently under study as a natural herbicide source.
Threat(s): The tree of heaven is a dominant tree that crowds out native species by its fast reproduction and aggressive range expansion; its suckers choke out native seedlings, greatly reducing local biodiversity. It invades urban spaces, blocking sunlight, views, and breaking up pavement and building foundations and blocking plumbing and sewer systems. In fact, in cities, this weed will grow virtually everywhere.
In the countryside, it is currently seen in fields, woodland periphery. and untended open spaces, preventing the propagation of native species. In agricultural environments, the tree of heaven pollutes fodder and damages farm equipment. It proliferates in sections of forest opened by gypsy moth predation.
Despite threats to native species, Alianthus seeds are still readily available in nurseries and seed catalogs in the United States.
Control Level Diagnosis: A. altissima is classified as an invasive, nonnative plant in many states.
Control Method: The entire area colonized by the tree of heaven must be treated over a long period of time for effective eradication. Young seedlings must be dug up, root suckers must be destroyed by removal or herbicide; cutting alone is ineffective as this action stimulates the stump to send out new suckers and sprouts. Careful application of plant poison to the bark in late winter is often effective on trees less than six inches in diameter; specific herbicides are listed on the National Park Service website.
Any method must be diligently and continuously pursued to eradicate this invasive weed. For the occasional stubborn individual tree, the Division of Forestry recommends flame-throwers and bulldozers as a means of permanent removal.
Natural control methodds are limited. The tree of heaven is preyed upon by very few insects due to the chemicals in its wood and bark. The fungus Verticillium albo-antrum kills A. altissima, but unfortunately the fungus spores remain in the area of the dead tree and will kill many species of native trees that might germinate in the infected location.
Brockman, C. Frank, Trees of North America, Golden Press, Racine, Wisconsin, 1968
Edlin, Nimmo, et al., The Illustrated Encyclopedia of Trees, Harmony Books New York, 1978
Hessayon, D.G., The Tree and Shrub Expert, Expert Books, New York, 1993
Little, Elbert L., National Audubon Society Field Guide to North American Trees, Alfred A. Knopf, New York, 1980
Mondadori, Arnoldo, ed., Simon and Schuster’s Guide to Trees, Milan, Italy, 1977
Stobel, Gary A., “Biological Control of Weeds,” Scientific American , 265:1 (July 1991), p.74.
Photo Credits: Mary Knight; illustration by Patricia J. Wynne