Question: A friend told me that the Tree-of-Heaven (Ailanthus altissima) in my yard is an invasive species and said I should get rid of it. Is that true and why? If so, what are recommended replacement trees?
Ailanthus altissima, commonly referred to as tree-of-heaven or paradise tree, originated in central China. It was first brought to Philadelphia from England in 1784 and was planted widely in the eastern United States in the early 1800s. It was valued in urban settings for its fast growth, tolerance for poor soils, low moisture and poor air quality, and resistance to diseases and pests. It has now become naturalized in 42 states. The Virginia Department of Conservation and Recreation has cited it as a highly invasive species, causing “economic and ecological harm, along with ongoing management issues”. In addition to the negative environmental impacts described below, invasive species, including tree-of-heaven, cost the US economy an estimated $120 billion per year due to damage caused by decreased productivity of timber areas and costs of control methods.
Tree-of-Heaven or a Look Alike Species?
First, be sure that you have correctly identified the tree before taking any action. Ailanthus altissima can grow up to 80 feet tall and 6 feet in diameter, with an open, uneven pattern of branches. Leaves are shaped like feathers, 1 to 4 feet long with 11 to 41 leaflets including a terminal leaflet. Leaflets have smooth edges with one or two bumps or teeth at the base. Male and female flowers grow on separate trees, forming large yellow-green clusters at branch tips. Seed clusters on female trees change from yellow to yellow-green or red-brown as they mature. When leaves are crushed, they have a strong, offensive odor which resembles cat urine or rancid peanut butter. Plant identification can be challenging. For more information on how to distinguish tree-of-heaven from its look-alike species, view this video or compare your tree with these photos.
Environmental Impacts of Tree-of-Heaven
Blue Ridge PRISM calls the Tree-of-Heaven a “furiously aggressive invasive” tree. Introduced on purpose or by accident from another country or region, invasive plants thrive in, and are a threat to, their new environment. Tree-of-Heaven certainly has the characteristics of an invasive plant species. Specifically, it:
- Reproduces prolifically, has multiple means of reproducing and spreads easily. A prolific seed producer, it invades cultivated fields and natural habitats where it grows vigorously – three to four feet per year – establishing dense stands. A female tree can produce between 300,000 to 350,000 seeds per year and resprouting occurs whenever the tree is cut or injured making removal difficult.
- Adapts readily to a wide variety of soil, moisture, and light conditions and quickly takes over sites that have been disturbed by land development. Today’s frequent land-use changes cause more disturbed areas and open land provides ample opportunities for invasive species to take over.
- Out-competes slower growing and less prolific native species, which results in loss of native plants. In addition, it produces chemicals that kill or prevent other plants from growing near it.
- Lacks natural predators to keep its growth in check.
- Changes how the native ecosystem functions by reducing and degrading the habitat that supports the number and diversity of plants and wildlife in the area. Opportunistic native wildlife, like white-tailed deer, can make the situation worse by selectively browsing only on native plants.
Control Methods
Removal of Ailanthus altissima requires diligence and monitoring – it can take as many as five years for a well-established tree to be completely eliminated because the remaining stump and root system will send up new shoots.
The type of control depends on the size of the tree. Some of the most common methods recommended by Blue Ridge PRISM follow.
- Manual or Mechanical: Pull or dig out the young seedlings by hand as soon as they appear, making sure to remove all the seedling roots. Moist soil makes the job easier. Note that root suckers cannot be pulled out since they are attached to bigger roots.
- Basal Bark: For small trees (4-6 inches in diameter), spray with a recommended herbicide on the lowest 12 inches of the trunks.
- Hack & Squirt: For larger trees, make a series of cuts into the trunk at waist height, leaving 2 inches between cuts. The best time for this method is June through October.
- Cut Stump: Mature trees can be cut down but require follow-up actions. The remaining stump will continue to produce many sprouts and the tree’s extensive root system will produce more suckers. Apply a recommended herbicide to the perimeter and sides of the stump. Continue to monitor the area after for new growth from the stump and roots. Sprouts from lateral roots may occur 50-90 feet from the parent tree. Target female trees, cutting in early summer when root reserves are lowest.
For more information on control methods and recommended herbicides in Virginia, refer to the Virginia Cooperative Extension 2021 Pest Management Guide for Home Grounds and Animals and the Department of Forestry’s guide to tree-of-heaven. Use chemicals only when recommended. Be sure to read the label before using any chemical control and follow the directions exactly to protect yourself and your landscape and avoid polluting nearby waterways.
Alternatives to Tree-of-Heaven
There are a number of good choices for replacement trees if you want a tree with a similar appearance. View this video to learn about the following native trees.
- Box Elder (Acer negundo)
- Black Walnut (Juglans nigra)
- Green or White Ash (Fraxinus pennsylvanica or Fraxinus americana)
- Smooth Sumac (Rhus glabra)
- Staghorn Sumac (Rhus tryphina) – this plant is a tree-of-heaven look-alike.
Want to know more about these and other native trees suitable for Virginia? Visit the Plant Virginia Natives website for links to a native plant finder, info on native tree selection and tree fact sheets.
And, there’s one more reason to control this particular invasive species. It is the preferred host for the Spotted Lanternfly, a new invasive insect pest, first sighted in Virginia in 2018, that has the potential to impact Virginia’s grape, orchard and wood-product industries, according to Virginia Cooperative Extension.
References:
“Control and Utilization of Tree-of-Heaven,” Christopher Asaro, Virginia Department of Forestry, 2019.
“Exotic Invasive Plants,” Gagnon, Jennifer, Extension Associate, Virginia Tech, Virginia Cooperative Extension, Publication 420-320, 29 Apr 2020.
“Invasive Plants”, Caldwell, Cathy, Piedmont Master Gardeners, The Garden Shed, Vol. 1 No.2, Feb 2015
“Invasive Tree-of-Heaven & Native Look Alike Identification Photographs”, Brooks, Rachel et. al., Virginia Tech, Virginia Cooperative Extension, Publication SPES-148NP, 25 June 2019
“Now is the Time to Tackle Tree of Heaven” Piedmont Master Gardeners, Timely Topic, 15, Sept 2020
“Tree-of-Heaven”, Penn State University, Penn State Extension, 2 Nov 2020
“Tree-of-Heaven or Paradise Tree,” Susan A. Roth, Blue Ridge PRISM, May 2017
“When Invasive Plants take root, native animals pay the price,” Amy Painter, Virginia Tech, Aug 7 2019
“Virginia Invasive Plant Species List”, Heffernan, K. et. al, Virginia Department of Conservation and Recreation, Division of Natural Heritage, 201
