Today it grows in places from Maine to southern California, and has infested hundreds of acres of oak-hickory forest in Shenandoah National Park in Virginia. Forest Service species review , it first arrived in Pennsylvania in 1784 as an ornamental plant. The tree-of-heaven has a lovely name and a rough reputation. So how did a tree planted for looks become a forest problem?
According to a U.S.
Pennsylvania introduced it in 1784, while New York used the tree for ornamental purposes in 1820. The eastern introductions came through English stock from China, and by 1840 eastern nurseries were selling the tree. It is referred to as one of the fastest-growing trees in North America, and saplings may average about 3 feet of growth per year for at least four years. Winged seeds are dispersed by the wind, and in one experiment , the seeds went farther than those of 37 other wind-dispersed species. One tree can produce more than 325,000 seeds in one year.
Because it had medicinal and cultural importance in their homeland, chinese immigrants who came to California during the Gold Rush, many of whom later worked on railroad construction, may have brought the tree. Because it re-sprouts from its roots; shoots can emerge up to 50 to 90 feet from the parent stem, and the wounded or dead main stem causes extensive root sprouting, killing the tree is not a solution. Because of that, the review states that fire is not recommended for the control of the tree.
This tree species is native to central China and Taiwan. The third introduction occurred during the California Gold Rush in the middle of the 1800s. The tree-of-heaven is designed to spread.
The review says that the distribution of this tree in North America seems to have occurred through three different introductions from China.
One possible answer is a fungus. The study also inoculated tree-of-heaven seedlings with isolates of the same fungus from other host plants, and those isolates did not cause disease in the seedlings. The authors wrote that the fungus is host-adapted and a strong biocontrol candidate. That’s promising, but the study calls it a candidate, not a done deal.
In 2014, a study in Phytopathology revealed that Verticillium wilt, caused by the fungus Verticillium nonalfalfae, had been causing the death of tens of thousands of tree-of-heaven trees in forests in Pennsylvania, Ohio, and Virginia . In field tests, however, an isolate taken from tree-of-heaven itself was highly effective: after researchers inoculated 100 trees across 12 stands, natural spread of the fungus killed more than 14,000 additional canopy trees by 2011, nearly wiping out tree-of-heaven in several of the smaller stands.
