Meet the Trees: Tree of Heaven
Ailanthus altissima, the tree of heaven is a tree with a troubled past. Before its first introduction into the United States in 1784, this tree species had been extensively cultivated in China. In China, its roots, leaves, and bark were used as an astringent in traditional Chinese medicine and its leaves were used to aid in silk production. Here in the U.S, however, it was known for its ornamental and durable qualities. Landscape gardeners appreciated the smooth grey bark of this tree and incorporated them into the English style landscapes of the late 1700s.
During the industrial revolution, coal soot, sulfur dioxide and acid rain led to the decline of many established urban trees. While many species declined, the tree of heaven proved to be indestructible. It is among the most pollution-tolerant of tree species, including sulfur dioxide, which it absorbs in its leaves. It can withstand cement dust and fumes from coal tar operations, as well as resist ozone exposure. Even high concentrations of mercury have been found in tissues of the plant without adverse effects.
Landscape gardeners looking to establish trees in difficult sites began planting Ailanthus from Massachusetts to Florida and west to California. By 1850, these trees were revered by a growing Chinese immigrant population in the United States who saw these trees as a symbol of home.
This tree was well established in the United States way before gardeners realized how dangerous this plant can be to native ecosystems. Not only are these trees robust seeders, but they are capable of resprouting from root fragments and will sprout from any damaged areas on the tree. To further gain Darwin’s advantage, Ailanthus produces an allelopathic chemical called ailanthone, which inhibits the growth of other plants. These attributes, combined with its ability to thrive in poor soils has created an extensive seed bed throughout the United States that displaces native plant communities.
By 1880, many Americans denounced the planting of Ailanthus in favor of planting trees native to the United States. Ecologically this was a sound process as plants native to their region form beneficial partnerships with other organisms. Unfortunately, the timing of this movement coincided with The Chinese Exclusion Act which prohibited the immigration of Chinese laborers. In the west, many urbanites blamed Chinese immigrants for the economic decline and used the problematic nature of these trees as an allegory for why chinese immigrants should not be allowed in their cities.
Few Ailanthus trees reach 50 years, some specimens have been known to exceed 100 years of age. Based on a 1963 survey indicating the same specimen tree, we know that this tree of heaven is at least 57 years old and is a lone male and will no longer produce seed, reducing the risk of it ever spreading from the Park. While the tree of Heaven might not be a good fit for future plantings in the United States, it is a tree that can inspire us to persist in every situation.
“There’s a tree that grows in Brooklyn. Some people call it the Tree of Heaven. No matter where its seed falls, it makes a tree which struggles to reach the sky. It grows in boarded up lots and out of neglected rubbish heaps. It grows up out of cellar gratings. It is the only tree that grows out of cement. It grows lushly…survives without sun, water, and seemingly earth. It would be considered beautiful except that there are too many of it.”
— A Tree Grows in Brooklyn, Introduction, Betty Smith