Invasive plant: the tree of heaven

The tree of heaven (Ailanthus altissima), also known as the Japanese varnish tree, is a tree belonging to the family Simaroubaceae that can reach a height of 25 to 30 metres. It originates from East Asia and was deliberately introduced into Europe in the 18th century for ornamental purposes, but above all in connection with silk production, as the plant served as a food source for a moth, the ailanthus silkmoth (Samia cynthia), which was intended to replace the mulberry silkworm (Bombyx mori).

This tree exhibits all the characteristics of an invasive plant: it adapts to all situations and all types of terrain, even polluted soils; it produces a large quantity of winged seeds that promote its spread by wind; it also reproduces by root suckering, with each root fragment capable of giving rise to a new individual; its rapid growth and extensive foliage intensify competition with local species.

The tree of heaven is a dioecious species, meaning that male and female organs are located in separate flowers borne on different trees (there are therefore male trees and female trees). The whitish-green flowers are grouped in clusters at the ends of branches; they bloom from June to September and are malodorous, due to foul-smelling – and highly allergenic – molecules produced by all parts of the plant. Despite this, they attract a wide range of pollinators, including honey bees, which assiduously collect the nectar, often to the detriment of other native melliferous species.

The honey produced from this nectar is of poor quality, its taste being frankly unpleasant, even when present in small proportions in wildflower honeys. Beekeepers therefore have an additional reason to combat the tree of heaven, a true ecological scourge!

See also:

• Invasive plants – general concepts
• Invasive plants: Asian knotweeds
• Invasive plants: Himalayan balsam
• Invasive plant: the butterfly bush
• The black locust or false acacia

Sources

J. Piquée, Les plantes mellifères mois par mois, 2014

T. Silberfeld, C. Reeb, Les plantes mellifères, 2016