Common Name: Tree of Heaven, Ailanthus, Paradise-tree, Copal-tree, Chinese sumac, Ch’un Shu (Chinese), Ghetto tree (slang) – In the Ambonese dialect of the Moluccan language, ailanto means ‘Tree of Heaven.’
Scientific Name: Ailanthus altissima – The generic name was derived from ailanto, the name given the tree by the inhabitants of the Indonesian Island of Ambon in the Maluku Archipelago. The specific altissima is Italian for ‘towering’ or ‘uppermost’ and refers to the physical size of the tree relative to the other species in the genus.
Potpourri: The Ailanthus or Tree of Heaven is a metaphor for survival in inhospitable places in both a cultural and ecological sense. It is the tree of the 1943 novel A Tree Grows in Brooklyn that epitomizes the cultural struggle of Francis Mary Nolan in overcoming the tribulations of poverty in the immigrant culture of New York City. It is a non-native tree that was purposely imported for horticultural purposes but thrived in the ecological struggle engendered by the pollution of America’s industrial cities. It has earned the pejorative sobriquet Ghetto tree to offset the empyreal Heaven tree. Ailanthus is also subject to aesthetic perceptual dichotomies; handsome to some, homely to others. The good, the bad and the ugly.
Ailanthus is a native of Asia, its introduction to North America a part of the global botanical exposition of the 18th and 19th Centuries that purposed Darwin’s role as naturalist on the HMS Beagle and Bligh’s breadfruit mission of the HMS Bounty. Pierre d’Incarville was a Jesuit priest dispatched to China in 1740 with the inimitable and ultimately unattainable task of converting the Qing Dynasty emperor to Catholicism. He did succeed in establishing his credentials as an amateur botanist, sending the seeds of Ailanthus among other plants to the Jardin Royal des Plantes in Paris. As the Linnaean classification system was in statu nascendi, there was no established taxonomy for the new tree. From Paris, where it was thought to be a sumac and was accordingly designated Rhus succedanea, it traversed the English Channel to the Public Garden at Chelsea, where it was called Toxicodendron altissima. The impetus for the identification and international exportation of new plant species was predominantly the colonization of the Americas, where agricultural enterprise was the economic engine and new plants the entrepreneurial initiative; the concept of invasive species was not yet manifest. René Desfontaines, the botanist at the Jardin Royal, noted that R. succedanea was not a sumac but an altogether new genus of trees (nouveau genre d’arbre) and published an article in 1788 entitled “Memoire sur un nouveau genre d’arbre, Ailanthus gladulosa,” establishing the etymological root of the genus in the Moluccan name for the tree of heaven: ailanto. It was not until 1916 that Walter Swingle of the USDA Bureau of Plant Industry combined the French genus with the English species to yield the modern officially recognized scientific name of Ailanthus altissima.
Ailanthus was widely planted in many European cities after its importation from China, the epithet “Tree of Heaven” likely the result of the public’s approbation. It was brought to the United States in 1784 by William Hamilton for plantation in The Woodlands, his prodigious Philadelphia estate of some 300 acres – now the Woodlands National Historic Landmark; it is also reputed to have been grown in the nearby Bartram Botanical Garden of the naturalist John Bartram where ancestors of the original tree still grow. The tree’s robust tenacity, rapid growth, and exotic, comely appearance appealed to the burgeoning population centers of the nascent nation. By the early 19th Century, small trees were available for sale in Flushing, New York, the site of the first commercial nurseries in the United States. It should come as no surprise that a tree with substantive growth potential would do what all plants do as a matter of evolutionary dynamics – by the end of the 19th Century it had escaped the cities and spread to the hinterland to perhaps become the first invasive species. It has been over two hundred years since its inception; its success has come at the expense of its perceived benefits. The Tree of Heaven has become an oxymoron.
The survivability of Ailanthus is a measure of its evolutionary adaptations. It thrives in diverse environments: from the subtropical to the temperate; from the very wet (up to 90 inches of rain a year) to near-arid (as little as 14 inches a year with 8 months of no precipitation); from a low temperature of 15°F to a high temperature of 97°F; and from a soil composition of loam to one that is rocky and acidic with a PH as low as 4.1. It is a prodigious seed producer; the panicled flowers extend half a foot in length with compound racemes. Each female flower (Ailanthus is dioecious which means there are male trees and female trees – both have flowers) produces hundreds of seeds and amature, healthy tree will grow several hundred flower panicles in one year. In a field experiment that compared Ailanthus with ten other canopy trees, it produced 40 times the number of seeds as its closest competitor with a production rate of 2,500 seeds per square meter. The seeds are in clusters called schizocarps; the name is descriptive of the splitting of the cluster into individual winged seeds (from the Greek schizein meaning ‘to split’ and karpos meaning ‘fruit’). The winged seed configuration is one of the most efficient adaptations for wind dispersal and Ailanthus is better than most if not all other trees – An experiment on Staten Island (vice Brooklyn) found that Ailanthus seeds traveled a greater distance than those of 37 other wind dispersing trees. Not only does it grow almost anywhere, it sends out mores seeds that go farther than any of its competitors.
Because of its success as an interloper, Ailanthus has gained and to some extent earned a reputation as an undesirable invasive plant; its other negative attributes have become manifest. First of all it stinks – literally. The male flowers emit a malodorous scent that hardly seems evocative of a heavenly tree. The copious, mephitic flowers are also
unsightly in winter, clustering in bunches that resemble pinkish shredded plastic bags. Secondly, its rapid epigeal growth is matched by its rapid hypogeal growth – the roots grow just as fast as the branches and leaves. This results in damage to buildings and other structures adjacent to the open areas to which it is inexorably attracted; sewer lines are a prime target since they contain water. The 800 year old Portuguese Sé Velha of Coimbra Cathedral suffered significant tile roof and mortar wall damage due to root penetration (A Tree Grows in Portugal?). Its third and most insidious negative attribute is also the least noticeable; it is allelopathic. Allelopathy is the ability of a plant to repress the growth of other plants by means of a chemical that is toxic to them (from the Greek allelo meaning each other, and pathetos meaning ‘subject to suffering’ – the plant equivalent to schadenfreude). The allelopathy of Ailanthus was first discovered in 1959 by Francois Mergen at the Yale School of Forestry; he demonstrated that it was toxic to 37 different gymnosperm (cone) trees including 21 pines in addition to 10 broad-leaf trees – only the white ash was immune. Recent research revealed that Ailanthus produces a chemical appropriately named ailanthone that is a one of the secondary metabolites called quassinoids that are characteristic of the Ailanthus Family Simaroubaceae. Secondary metabolites are compounds produced by plants that have no known role in growth or reproduction. It is now hypothesized that these compounds evolved to protect the host plant from either predation by animals by acting as pesticides or from competing plants by acting as herbicides. Ailanthone is such a powerful herbicide (0.7 ppm reduces growth by 50 percent) that it is being considered as a natural alternative to artificial chemical products.
In Asia, the Tree of Heaven is neither bad nor ugly. It is mostly good and has been since the dawn of recorded history. Ailanthus appears in the Erya (sometimes Erh-ya), the first Chinese encyclopedia that first appeared in the 3rd Century BCE, an incunabulum that is considered one of the thirteen Confucian Classics. The ideogram for the Ailanthus is a combination of one symbol for ‘spring’ and one for ‘wood,’ the tree being one of the first to form buds in the spring; a harbinger of an end to the winter’s deprivations. A North China nursery rhyme translates to “As the unfolding buds of Ailanthus appears, the helpless white eyes of the starving people turn clear.” That it was a tree imbued by the Chinese with cultural importance is clearly manifest in the use of the Ailanthus as a symbol for father, its majesty and grace like that of the mighty oak in European cultures. Ailanthus is similarly valued for its practical use as a lumber and firewood tree; the rapid growth of non-warping dense hardwood with heat-producing capacity of white oak and black walnut has made it a valued commodity species.
However, there is another significance of Ailanthus tree in Asian culture that transcends the traditional arboreal association; it is widely used as an herbal medicine. This, too, is a matter of historical practice; it first appears in Materia Medica, an imperial collation of remedies ordered by the T’ang Dynasty in 656 CE. While the leaves were proscribed as poisonous if taken internally, their use was prescribed after boiling as an external treatment of skin ailments such as boils and rashes. Dried Ailanthus bark was and still is a marketed herbal in China, appearing in the 1960 rendition of Materia Medica as the sanctioned drug ch’un-po-p’i (white bark of ch’un). It is used sparingly for the treatment of dysentery (intestinal hemorrhage) and for menorrhagia and spermatorrhea, medical problems associated with female and male sexual organs. The use of Ailanthus as an herbal remedy was so prevalent that the Chinese who came to California in middle of the 19th Century to work on the Central Pacific Railroad brought it with them. Recent research has revealed that Ailanthus is chemically complex and that its constituent extracts have antibacterial and anti-inflammatory properties that may be useful in the treatment of cancer.
Ailanthus is also good at growing in bad places. According to Charles Sargent, the founder of Harvard’s Arnold Arboretum, “for hardiness and rapidity of growth, for the power to adapt to the dirt and the smoke, the dust and the drought of cities, for the ability to thrive in the poorest soil, for beauty and for usefulness, this tree is one of the most useful which can be grown in this climate.” The need for additional carbon dioxide absorption afforded by reforestation as an offset to its generation by combustion is an urgent mandate for the 21st Century. The drought inducing evaporation of elevated global temperatures is a problem that, at least in part, the drought tolerant Ailanthus could ameliorate. It can be argued that it is a “good invasive” as it has been noted that it has not spread to intact forest ecosystems even though it has had over 200 years to do so; it was ranked the least invasive of 18 introduced plants by the Oak Ridge National Environmental Research Park. Perhaps it is a Tree of Heaven after all. We need one.