Ailanthus, Tree of Heaven (Ailanthus altissima)

Ailanthus is a 5-30 m tall, deciduous tree with a maximum trunk thickness of 80 cm in diameter and light gray bark. The leaves are arranged alternatively, along an extended stem, which ends in a leaf (similar to a walnut tree). When bruised, the leaves emit an unpleasant odour, which repels insects. This is why the species hardly has any natural enemies. The flowers are small, yellowish green, and appear in panicles. The pollen has an unpleasant smell. The fruit have a “wing”, which allows them to spin quickly and spread across large areas.

The species is native to China and North Vietnam. It was introduced to Europe in 1740 for decorative purposes, as well as, by mistake, for the furniture industry, because it was mistaken for the Japanese lacquer tree. It is distributed throughout the entire world, except Antarctica. It came to Bulgaria as a decorative tree in 1888, and spread massively throughout the whole country.

It is distributed up to an altitude of 1800 m a.s.l. and has no particular soil or condition requirements. It grows on dry, as well as moist soil. The species is one of the trees with highest resistance toward air pollution.

Ailanthus grows quickly, taking over diverse terrain, including arable land. It forms many seeds, replacing local species. Forms dense groups. The vegetation of natural pastures and meadows is gradualy replaced by shrubs and low ailanthus forests. This makes their use for grazing and mowing difficult. The invader secretes a substance, which does not allow other species to grow and leads to their death. Its roots spread out widely and deeply, damaging sewage pipes, archeological sites, building foundations and creating risks to the stability of infrastructure and the integrity of cultural heritage.

Ailanthus is one of the most dangerous invasive alien plant species in Europe, with the most serious adverse impact on biodiversity and the economy. It is therefore included in the List of invasive alien species affecting the European Union for which concerted action is required from all Member States (the Union list).

Cutting only stimulates the development of the species. Special measures must be taken in the fight against this invader!