Invasive species: Heavenly tree actually from hell

Invasive species: Heavenly tree actually from hell post thumbnail image

How much do you know about invasive species? Would you be able to identify one in your surroundings? Many gardeners and nature lovers answer ‘no’ to this question, so we launched a feature showcasing some of the listed invasive species in South Africa. Join us in exploring and learning more about these species and why they are declared invasive in South Africa. Our first feature looks at the tree of heaven, also known as the tree of hell (Ailanthus altissima).

Don’t ever think you will plant one tree. Where there is a single tree, dense clumped together tree stands will develop, slowly spreading. This is why this tree earned the nickname tree of hell in South Africa. It can grow almost a meter a year, which may sound great if you want something fast-growing, but steer clear. The tree clones itself via underground suckers or through the hundreds of thousands of seeds each tree produces annually.

Tree of heaven against a blue sky
Tree of Heaven growing in a nature reserve in South Africa.

The tree of hell is a deciduous tree native to China, Taiwan and the Himalayas and often grows and spreads rapidly in disturbed or urban areas. It tends to crowd out native plant species. Tree of heaven/hell is a declared invader in South Africa.

Why does the tree of heaven do so well?

The tree of heaven is a hardy and resilient tree that can grow in a wide range of soil and climatic conditions. In many parts of the world, including Europe, North America and South Africa, the tree was first planted as an ornamental tree. It grows fast and can colonise disturbed areas such as abandoned lots, roadsides, and industrial sites.

The tree has large compound leaves that can grow up to a meter long, with a distinct odour when crushed. It produces large clusters of small yellow-green flowers in the summer, followed by winged fruit that disperses easily with wind.

Why is the tree of heaven a problem?

The tree of heaven, or tree of hell, is now considered an invasive species in many parts of the world, not just in South Africa. It easily outcompetes native plant species and reduces biodiversity. It also causes structural damage to buildings and sidewalks, as its roots can grow and crack pavement.

But pavements and buildings are not where it stops. The tree of heaven is problematic because it reproduces fast and aggressively inhibits (and can even kill) native plants near it. This invasive plant produces seeds abundantly, crowds out native species by forming dense thickets and secretes a chemical into the soil toxic to surrounding plants. The leaves can also cause skin irritation, leading to itchiness and a persistent rash.

Controlling the tree of heaven

Getting rid of invasive species is not always as easy as it might seem. Identifying and eliminating seedlings before their taproot matures is the most efficient control method. When pulling or digging, extract the entire root system, comprising all roots and fragments, to prevent regrowth. Any suckers and lateral roots that remain will regrow, so you might have to use a herbicide, or just be persistent.

A listed invasive species

The tree of heaven is a Category 3 NEMBA – Category 1b invasive species, which means: 

Category 1b: These are established invasive species that must be controlled and, wherever possible, removed and destroyed. Any trade or planting is strictly prohibited, and landowners must control Category 1b plants and animals on their properties. A species management plan should be drafted for large properties.

It is already a problem in the Western Cape, Eastern Cape, Free State, KZN, Mpumalanga and Gauteng.

Still unsure? How to identify the tree of heaven

Blossoms of the Tree of Heaven up close
Blossoms of the Tree of Heaven up close. Photo: Hans from Pixabay

Height and appearance of the tree of heaven: Grow to 20m or more. It has smooth stems with pale grey bark and light chestnut brown twigs, especially in the dormant season.

Tree of heaven bark: Grey, smooth or scaly bark.

Typical tree of heaven leaves: Dark green leaves, with yellowish autumn tints that give off an unpleasant odour when crushed.

Tree of heaven flowers: Greenish-yellow flowers, in large terminal sprays, from October to November.

Fruit/seeds of the tree of heaven: Papery winged fruit, tan pink-coloured.

A word of caution about invasive species

Removing invasive species is always good, but never remove a tree just to cut down a tree. Trees offer homes to birds and other species but also provide shady areas in our home gardens. When you remove an invasive species check that there are no nests in the specific tree. The next step would be to plant an indigenous alternative.

Alternatives to the tree of heaven

Planting indigenous alternatives should always be a priority over exotic or invasive species. However, a plant thriving in the desert will also not necessarily do well in KwaZulu-Natal, so the best option is always to identify local indigenous species that can do well in your specific climate. Botanical Gardens and local indigenous nurseries are often good places to start and ask for advice.

Some indigenous nurseries in South Africa to get you started:

Random Harvest (Kugersdorp) www.randomharvest.co.za/

Grow Wild purposefully indigenous (Midrand) www.growwild.co.za/

Witkoppen Wildflower https://witkoppenwildflower.co.za/

Happy by Nature (Cape Town) https://happybynature.com/

Fynbos Life (Cape Town) https://www.fynboslife.com/nursery/

Good Hope Gardens (Cape Point) https://www.goodhopegardensnursery.co.za/

Skukuza Indigenous Nursery (Kruger National Park) https://www.sanparks.org/docs/parks_kruger/nursery/nursery-pamphlet.pdf

The Indigenous Nursery (KZN) https://www.instagram.com/the_indigenous_nursery/

Dr Boomslang (Kommetjie, Cape Town)https://drboomslang.co.za/

Alternatively, contact your nearest National Botanical Garden

Have you seen a tree of heaven in your surroundings in South Africa? Researchers are calling on all citizen scientists to report sightings. You will need to know the exact GPS location of the tree, take a photo, and then mail the information to Lyriche Drude at treeofheaven.wits@gmail.com or upload it to www.inaturalist.org.

Main image: Hans from Pixabay

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