If you travel throughout Europe, particularly the south of France and Spain, you’ll see whole areas, particularly urban areas, swallowed up by the Tree of Heaven. This scurge is also present throughout South Africa, colonising large areas of vacant land. In Knysna it has invaded areas along the Saltriver, along the N2, and also near the Provincial Hospital. It was imported from China as an ornamental; the quick growth, attractive foliage and resistance to pests and diseases made it a desirable tree decades ago.
Dubbed the “Tree of heaven” for its eagerness to reach up to the sky, Ailanthus altissima has invaded large parts of urban areas in South Africa, despite the angelic common name, it has a distinctly sinister side. The tree produces a chemical known as ailanthone that prevents the growth of other plant species nearby, has a smell like rancid cashew nuts and sends out a mass of suckers that smother other plants. It has a very thick underground root system that puts up shoots every five to 10 centimetres creating very, very dense thickets. The tree initially grows by as much as four metres a year – more than a centimetre a day – although between one and two metres is more usual.
The tree’s roots are so strong and spread so rapidly that they can cause havoc in urban areas, pushing up through buildings, breaking up paving, walls and sewer systems. The tree of heaven is capable of re-sprouting from both root fragments and exposed tree stumps.
Physical contact with this tree, particularly with the leaves, can lead to skin irritation and, if left untreated, can cause severe itchiness and a persistent rash resulting in high levels of pain and discomfort.
Controlling & Managing Tree of Heaven
Why should we be concerned about the tree of heaven? It is a prolific seed producer and can thrive in even the most unfavourable conditions with little management. The most effective way of control is to pull seedlings by hand before the tap root develops, however care needs to be taken to ensure that no root fragments are left in the soil. If the plant has matured, cutting alone will only help temporarily by reducing its ability to spread. Eradication of larger trees is a more difficult undertaking.”