Conservationists remove invasive locust trees in hundreds of hectares of the large herbivore reserve
The black locust is one of the most troublesome invasive woody plants threatening European nature, and therefore conservationists started removing this non-native species this summer in an area of 350 hectares of the large herbivore reserve referred to as European Serengeti. It is located in the former military training area of Milovice near Prague.
“The spread of non-native species is one of the greatest current challenges in nature conservation. Therefore, the utmost attention should be paid to their elimination. With the help of volunteers, we have been removing invasive plants such as the large-leaved lupine and Canada goldenrod in the large herbivore reserve for several years now. We have also begun removing dangerous locust trees with the help of experts,” said Dalibor Dostal, director of the European Wildlife conservation organisation.
Last year, the intervention was preceded by monitoring individual locust hotspots. “Locusts are not found throughout the entire reserve, but they grow in dozens of isolated hotspots, from where they are gradually spreading. That’s why it is necessary to intervene to stop their expansion,” explained Dostal.
In fact, dozens or even hundreds of invasive woody plant specimens can be growing at one site. “We’ve counted around 350 individuals in a relatively inconspicuous group of locusts,” enumerated Pavel Brodecky, who is part of the effort to eliminate locusts in the reserve using a method that was tested by experts in Podyjí National Park on the Czech-Austrian border in previous years. A hole is drilled in the trunk of a locust and a small herbicide dose is injected. The herbicide reaches the roots, killing the tree. Thus, no area-wide spraying is needed and no chemicals leach into the surroundings.
It is the summer dry season in particular that is a suitable period for this measure. “The tree has already completed its main growth and more reserve substances start flowing to the roots, so it responds significantly better to the injection than in other periods of the year,” adds Brodecky. His words are confirmed by the dried-up crowns of locusts that died just several days after being injected.
European bison especially enjoy gnawing on young locust trees. They often peel the bark off them, so the trunk dries up. However, the resistant tree often sprouts from the roots, even several metres from the original trunk. The locusts reacted in the same way to procedures that conservationists tested in the initial years after the reserve was founded. Cutting to a tall trunk or removing a strip of bark on a part of the trunk girth. Both methods are referred to in the literature as efficient ways of disposing of locust trees, but in practice they have resulted in rejuvenation from the roots in most of the trees. Afterwards, a dense cover sprouted in place of a single tree. Therefore, experts started disposing of locusts in the reserve by employing the injection method this year.
“The control of locust trees is essential particularly in open sites, where steppe and grass communities, which are important for various insect and plant species, are rapidly becoming overgrown with these invasive woody plants,” specified Jan Pergl of the Institute of Botany of the Czech Academy of Sciences.
The first phase in the large herbivore reserve should be completed this year. “Experts should manage to inject all of the mapped locusts roughly by the end of the summer. Next year the site will be mapped again and the measure will be repeated for woody plants that have survived this year’s injection,” concluded Dostal.
Locust trees (Robinia pseudoacacia) originate from North America and they have been spreading uncontrollably in Europe, pushing out native plant species. They excrete poisonous allelopathic substances through their roots into the soil that limit the growth of other plants. In addition, they cause the nitrification of the soil and change its composition, which is beneficial to only a few nitrophilous plant species such as nettle and elder. Locust trees form dense stands shade the site, causing flowers and the butterflies dependent on them and other native species to disappear. In addition to locust trees, the most problematic invasive woody plants in central Europe also include Chinese sumac, black cherry, box elder and red oak.
Photo: Ondrej Brodecky
