Tree-of-heaven – Ailanthus altissima (Mill.) Swingle

Since its introduction to North America as an ornamental, tree-of-heaven has become widely established in cities, along railways, roads, and riverbanks, and in a broad range of other habitats. Tree-of-heaven outcompetes native vegetation and dominates sites where it becomes established through a combination of rapid growth, vigorous root suckering, and production of chemicals that inhibit the growth of other plants. Prolific production of wind-dispersed seeds has enabled tree-of-heaven to easily spread from locations where it has been planted. Once established, tree-of-heaven is difficult to remove and its powerful roots can damage infrastructure like sewers, foundations, and sidewalks. In some people, tree-of-heaven pollen causes allergic reactions and exposure to tree-of-heaven sap or plant parts can cause skin irritation. Tree-of-heaven is also the preferred host of the spotted lanternfly, an invasive insect that is regulated in Canada because of its threat to the Canadian grape, fruit tree, and forestry industries, as well as the environment. Spotted lanternfly can become a nuisance pest in urban areas because individuals tend to cluster in large numbers.

Where it's found

In Canada, tree-of-heaven has been found in locations in British Columbia, Ontario, and Quebec.

Tree-of-heaven is best known for invading cities, but grows in a wide variety of habitats, including along roads, riverbanks, and rail corridors, and in agricultural fields and forests. Tree-of-heaven is native to China, but is now found on every continent except Antarctica. In the United States, tree-of-heaven is widespread.

What it looks like

Tree-of-heaven is a tree that can reach 30 metres in height. It has thin grey-to-brown bark that is smooth when trees are young and becomes rougher as trees mature. Tree-of-heaven has alternate compound leaves made up of 11 – 41 leaflets with smooth edges, except for one or more glandular teeth (round or pointed lobes that contain small glands) at the base of each leaflet (see Figure C).

Compound leaves are up to 1 metre long and individual leaflets are 5 – 15 cm long. Tree-of-heaven is sometimes referred to as stinking sumac because its leaves emit a foul odour when crushed. Tree-of-heaven produces large clusters of small flowers that are pale yellow to green. Individual trees are either male or female; female trees produce large numbers of single-seeded fruits that are 3 – 5 cm long. The fruits are winged and often twisted, and turn red or brown in summer and into autumn.

Lookalikes: Tree-of-heaven resembles several plants that are native to Canada. Similar native species include staghorn and smooth sumac and black walnut. Tree-of-heaven can be easily distinguished from these native lookalikes: staghorn sumac, smooth sumac, and black walnut have leaflets with toothed edges.

How it spreads

Intentional planting has been the most significant factor in tree-of-heaven's introduction to new regions around the world. Once introduced, it can easily spread by seed or by root suckering and re-sprouting.

Seeds and roots can be spread by vehicles and machinery.

What you can do about it

• Do not plant tree-of-heaven.
• Ensure vehicles and machinery are free of soil and plant parts prior to movement.
• Consider removing tree-of-heaven from your property to limit the spread and impacts of spotted lanternfly.
• Look for tree-of-heaven in cities, agricultural fields, forests, forest margins, along roadsides, riverbanks, and rail corridors, and in other disturbed areas. Tree-of-heaven sightings can be reported using the online app of your choice (e.g. iNaturalist or EDDMapS).