Invasive species (II): Ailanthus altissima

We continue the series of posts dedicated to invasive species, with the well-known ailanthus or tree of heaven Ailanthus altissima.

This tree can be seen in a wide variety of natural and anthropized spaces, for example, from the edge of roads and gardens to riverside areas.

Throughout our experience, we have found it in countless places, the last of which is close to the banks of the Jucar River in Tarazona de La Mancha (Albacete).

It is native to China, where it is cultivated as food for a species of silkworm, and from the north of Vietnam. It was introduced in the form of seeds in France in 1740 and, later (1751), when it was confused with the species Toxicodendron vernicifluum, was transported to London and other parts of Europe and America, expanding as an invasive species on all continents except Antarctica. In our country, it is considered an invasive alien species, appearing both in the Spanish catalog of invasive alien species as in the Atlas of invasive alien plants in Spain.

It is characterized by being a pioneering species, that is, it takes advantage of open spaces for colonization, with rapid growth. It blooms from May to July, reproducing well by seed, mainly with anemochoric dispersion, each adult specimen being able to produce up to 350,000 seeds per year, as well as asexually through vigorous vine and root shoots, which can be emitted even at a certain distance from the mother foot (up to 15 m). The leaves and bark have substances with allelopathic and herbicidal action (mainly ailanthone), which are toxic to many species, contributing to the reduction of native vegetation due to competition and being subject to low herbivorous pressure.

It has a sunken crown and reddish twigs; of compound, alternate, pinnate, ovate or lanceolate leaves.

It resists very adverse environmental conditions, such as extreme temperatures and summer drought, as well as the polluted atmospheres of large cities. On the other hand, it is very undemanding when it comes to the quality of the substrate, as long as it has sufficient drainage. It develops well both in full light or under shade.

Ailanthus is very difficult to eliminate once it has been established, sometimes persisting even after felling, burning or herbicide treatment. The first methods to be used are mechanical, starting with manually removing the seedlings as soon as possible, preferably when the soil is moist to facilitate the extraction of the entire root. In adult individuals, periodic felling must be carried out, which, although they do not cause the death of the tree, do prevent seeds from continuing to be produced.

These mechanical treatments, to be fully effective, must be combined with phytoncide applications, either foliar or by smearing the stumps; among the products being used, one of the best known is glyphosate. With regard to biological control, several phytopathogenic fungi have a certain capacity as control bioagents, such as Verticilium dahliae and Fusarium oxysporum, that have been isolated from dead or diseased trees in the United States.

It can produce effects on the habitat, species and economic resources associated with the use of natural heritage; for example, it has been proven to alter the availability of nutrients in the soil, increasing the total nitrogen content and decreasing the C/N ratio, in addition to increasing soil pH; due to its rapid growth and allelopathic effects, it displaces pre-existing natural vegetation or hinders its regeneration in the future, inhibiting the growth of other species; leaves and flowers, especially those of male specimens give off a fetid odor, and if bees visit the flowers of this species, they give off an unpleasant taste to the honey. It can cause damage to the sewer system and to the foundations of buildings.

From the area of agroforestry consulting From Ideas MedioAmbiental we advise on the control, propagation and eradication of the species.