We have started a new approach to tackling one of the most problematic invasive woody plants in the Danube Floodplains: the tree of heaven (Ailanthus altissima). This time, however, we are not using chainsaws or chemicals. Instead, we are bringing in nature’s helper: a fungus from the genus Verticillium.
But why is tree of heaven unwanted in nature around Danube?
At first glance, this species may not appear threatening. It grows quickly, is inconspicuous, and thrives almost everywhere. And that is precisely the problem.
This non-native woody plant spreads extremely aggressively, especially in sensitive habitats such as floodplain forests and river floodplains. It forms dense stands and secretes substances that inhibit the growth of other plants (a process known as allelopathy). It can also damage infrastructure through its root system. Without intervention, it quickly crowds out native vegetation, creating monotonous stands.
So, how does the Verticillium help?
This soil fungus causes ‘vascular wilt’, whereby the tree’s conductive tissues become clogged. This results in the gradual dieback and death of the plant. It thrives in moist environments, so it is not necessary to apply it to a perfectly healthy tree.
This method has already been successfully tested in several European countries and has proven to be gentle and long-lasting. The fungus only attacks tree of heaven, so it does not pose a threat to native species.
And what next?
We’ll be watching closely to see how the cobwebs react to the injection. We don’t expect miracles overnight – the goal is a gradual weakening of the stands to make room for the return of native species. Combined with other measures (such as wetland restoration, the introduction of grazing on the locale, and the restoration of native riparian forests), this is a beautiful example of how nature itself can help us solve problems.