Common Name: Tree of Heaven, Ailanthus, Chinese Sumac, Stink Tree, Tree from Hell, Ghetto Palm
Plant Family: Simaroubaceae, the Tree of Heaven family
Identifying Characteristics: Large, odd-pinnately compound leaves that are dark green with a sometimes reddish tinge. Young leaflets are bright green and waxy. Leaves and flowers are foul smelling (sometimes compared to dog urine), especially when crushed or torn. Male and female reproductive parts are on separate trees. In summer to fall, ther are dense clusters of reddish, winged seeds on female trees. These trees are easily confused with sumacs, especially when smaller, but sumacs in Denver tend to have "droopier", serrated leaflets, rougher bark, and a bushier habit. They also have bright red, fuzzy berries, which are easily distinguished from the winged seeds of Ailanthus.
Related species: Most of the simaroubaceae are tropical, so no close relatives exist in Denver. While ailanthus looks very similar to sumac, the two are only distantly related. Ailanthus is more closely related to the citrus family than it is to the sumac family (which includes cashews, mangoes, and poison ivy).
Duration: Woody and Deciduous
Habit: Canopy Tree
Successional status: Forest gap species. This species is intolerant of full shade, but given minimal amounts of sunlight, seedlings will bolt up as much as 10-15 feet per year, until they reach the full sunlight of the canopy. While the species is not technically very competitive, its roots secrete alleopathic chemicals, i.e. toxins that poison susceptible nearby plants.
Denver Native: No. Originally from China, it was introduced to the east coast in 1784, and has since spread across the entire US. It has also escaped cultivation in almost every other part of the world, but it hasn't presented as much of a problem (relatively speaking) in other places as it has in North America.
Weedy: Very. It seeds prolifically, has a very high germination rate, and resprouts from wounds and root fragments.
Useful or Beautiful: Some might call this plant beautiful, at least in terms of its reddish leaves and seeds, but its toxic personality might distort that image. Though Ailanthus can be used for lumber or firewood if very carefully selected and prepared, it may be more trouble than it's worth. Because Ailanthus trees tend to grow crookedly and have a corky pith, it is very difficult to find long, straight sapwood suitable for lumber. Also, due to the high moisture content and low density of the wood, it tends to cup, twist, warp, split, and even mold. Nearly all parts of the tree are used in traditional chinese medicine, primarily due to its astringent and biocidic and properties. However, as with most medicinal compounds, high quantities can be toxic.
Control Methods: In this case, the best offense is to be swift, brutal, and merciless. The first course of action should be to remove any mature female trees, to prevent additional seedling recruitment. Although it is probably desirable to remove the tree entirely, girdling is an effective method of killing the above-ground portion of the tree. However, with either method, any roots left in the ground will send up shoots. Unfortunately for those who prefer to have chemical-free gardens, herbicide chemicals are the only reliable way to kill adult trees. Although there are currently several biocontrol fungi being developed commercially, they are not currently available. Fortunately, the most effective methods, cut-stump, basal bark, and injection, are very targeted.
For more information: Check out this plant on invasivespeciesinfo.gov, the forest service (pdf), the Virginia Department of Forestry (pdf), the University of Maryland (pdf), or the National Parks Service.
Ugh! Nightmare!
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