How swamp crabs and co. threaten urban nature
muskrat, swamp crab, tree of paradise – some of the introduced species spread rapidly in Berlin. Other cities also struggle with invasive species. What can you do about uninvited guests?
aThe American swamp crawfish was first seen in the meadows and trails of Berlin-Tiergarten in 2017, causing quite a stir. Presumably, the offspring of the abandoned animals initially bred unnoticed before starvation or lack of space drove them out of the garden waters.
Each summer, samples of the invasive species, which are actually native to the southern United States and northern Mexico, are now caught out of the water. Further spread must be prevented and the spread must at least be slowed. The voracious and migratory animals are a threat to local species and ecosystems – not only in Berlin, but throughout the European Union.
Many other species that were not native to Berlin have spread to Berlin and other cities, and some are causing problems: giant hogweed, sky tree and narrow-leaved waterweed, as well as Egyptian goose, raccoon, and quipu. According to the Federal Agency for the Protection of Nature, about 900 species have settled permanently in Germany since 1492 – the year of the discovery of America, which scientists use as a border to distinguish foreigners from natives.
Fischer Senate Management Committees
66 species of animals and plants are included in the list drawn up by the European Union Commission, the so-called Union’s List of Invasive Species. Member states must prevent the introduction of these species or stop their unauthorized spread once they have arrived.
“In the case of species that are not yet indigenous here, you have a very good chance of turning them away,” says Ingolf Kühn of the Helmholtz Center for Environmental Research (UFZ) in Halle. “With species that already exist, such as swamp crab or giant hogweed, they can no longer be eradicated. Then it comes to the issue of containing stocks and keeping species away from particularly sensitive areas such as nature reserves.”
In Berlin, the Senate administration tasked a fisherman with emptying traps laid at least twice a week during the high season. The animals are sold to Berlin restaurants, among others. However, the knife and fork can rarely be used against invasive species – and combating them is often a task for Sisyphus. “There is often not enough capacity for that,” says Sebastian Kohlberg, a species protection advisor at Naboo. “Low nature conservation authorities simply lack financial and human resources.”
Relying relentlessly on driving out invasive species is often inappropriate, Kohlberg says. Focusing all efforts on managing one type of conflict is not a sustainable strategy. It often makes sense to strengthen the health of the ecosystem as a whole.
Demonic Gods Tree
“Especially with plants, many starters do not cause any problems, quite the contrary,” says wildlife expert Dirk Elert of the Department of Environment in Berlin. “Our gardens would probably have a much smaller number of species if there were no new plants.” In general, nature is constantly changing – as is the assessment of animal and plant species.
“The tree of paradise, which originated in China, was planted here about 250 years ago and has been cherished and cared for as a beautiful city tree for a long time,” says Eilert. “About 80 years ago, the species was spreading widely because winters are getting warmer and young trees sensitive to frost are increasingly surviving.” It can damage roads and walls.
Several species considered problematic today were deliberately introduced: the raccoon, for example, as a source of fur, and the Asian lady beetle for biological pest control. Today they are a species that can no longer be expelled.
With climate change, the situation is unlikely to improve in the coming years. According to the researcher at UFZ Kühn, the frost-loving species can become less. However, the majority of introduced species come from warmer countries and will benefit from the expected changes.
“Back off the beginnings,” says wildlife expert Ellert. “Once a species has established itself, there is often little chance of getting rid of it.”