Native to China and Taiwan, tree of heaven (Ailanthus altissima) was brought to the United States in the late 1700s and became a popular ornamental shade tree in urban, agricultural, and forested landscapes. Tree of heaven is highly adaptable, withstanding several different climates across the U.S. In 2012, Washington State classified this invasive species as a class C noxious weed due to its damage to native plants and ecosystems. Here is how you can identify and prevent the spread of tree of heaven in your region!
How to Identify: Tree of heaven has several unique identifiers that differentiate the species from other vegetation. Reaching over 60 feet in height, tree of heaven grows rapidly in dense colonies. A dioecious species (separate genders), the trees can form colonies or “clones” that are the same gender. Female trees can also reproduce by spreading seeds, producing upwards of 300,000 seeds annually. Tree of heaven leaves are pinnately compound, having a central stem with leaflets on each side. Leaflets are dark green in color and lance-shaped, having smooth edges and glandular teeth near the base. Flower clusters are found at stem tips, taking on a light green to yellow hue. These clusters appear in late spring and summer, becoming seed samaras as weather cools down. Over time, tree of heaven bark changes color, starting off brownish green and becoming brownish gray when mature.
Tree of heaven twigs are covered in fuzz and appear reddish-brown in color, setting them apart from similar looking species such as sumac, ash, and black walnut trees. One of the most unique characteristics of this species comes from tree of heaven’s foul and pungent odor. This smell derives from pollen produced by male flowers and resembles burnt peanut butter. The foul scent has led horticulturists to utilize female trees in urban areas, while male trees are found most in rural landscapes.
Spread: Tree of heaven grows and spreads quickly, making the species extremely difficult to eradicate once introduced to an area. These trees spread by cloning and seeds dispersed via wind and can germinate in a variety of soil and site conditions including nutrient poor soil, high temperatures, and areas with pollution or droughts. As mentioned above, female tree of heaven has high seed production in addition to good seed viability. Trees can start producing seeds as young as two years old, persisting in the seed bank for no more than two years. Tree of heaven can also reproduce through vegetative reproduction, as cut or injured stems or stumps can resprout 50 to 90 feet from the parent tree.
Impact: Tree of heaven poses a major threat to surrounding native species, producing allelopathic chemicals that make soil inhabitable for other plants. These trees can be hazardous to pavement and infrastructure, due to its rapid rate of spread and growth. In addition to its fast colonization, tree of heaven attracts spotted lanternfly; a highly destructive invasive species that causes extensive damage to agricultural commodities as well as urban and wildland trees.
Prevention: There are several ways to prevent the spread of tree of heaven. For one, proper disposal of cut or injured stems can prevent resprouting. Disposal information can be found on the Washington Noxious Weed Control Board website. Manual removal of trees may also deter the spread of this invasive species. When removing by hand, be sure to dig up the root, as mowing or cutting plants will lead to resprouting. Because tree of heaven cannot survive in heavily shaded areas, creating a dense canopy of plants will make the environment uninhabitable for this species. Herbicides may also act as an effective control method. For advice on chemical control and how to effectively apply these methods, find and contact your county weed board here.
Recently, the Washington State Invasive Species Council, Washington State Department of Agriculture (WSDA), Washington State Noxious Weed Control Board and other agencies have asked the public to look for and report tree of heaven and spotted lanternflies to help officials develop a plan to protect Washington against these invasive species. Sightings can be reported on the Washington State Invasive Species Council website and will aid officials in better understanding the distribution of tree of heaven before the arrival of spotted lanternfly.