Street life of a special kind: Even street medians can provide a habitat for a surprising number of insect species - if they are greened with the right plants. This is shown by a study of the residents of three test areas that were created as part of the “Urban Green” project in Berlin. The researchers found a total of 400 insect species there - including species that are on the Red List of Endangered Species.
The smelly city traffic rushes past them on both sides: the street medians are some of the most inhospitable green spaces that cities have to offer. But even in these extreme locations, efforts to bring more nature back into residential areas are apparently not in vain: for a few years now, researchers in the “Urban Green” project in Berlin have been exploring the extent to which the city's street medians can be greened with native plant species. It was shown that some plants can also cope with the enormous challenges of this habitat: they can withstand pollutants, road salt, drought and poor soil quality.
It crawls and runs in various ways
At least as far as the flora is concerned, these extreme areas can be made more natural. But to what extent can they also provide a home for insects? A team led by Frank Koch from the Museum für Naturkunde – Leibniz Institute for Evolution and Biodiversity Research in Berlin (MfN) investigated this question. Since 2017, the researchers have been taking a closer look at the six-legged residents in three of the project's test areas: every two weeks, they recorded the insects living there on the median strip in Frankfurter Allee, Adlergestell and Heerstraße.
As the MfN now reports, the researchers found a diversity of species at all three locations that significantly exceeded their expectations. They were able to identify a total of around 400 different insect species from six different orders. Not only were well-known survival artists among them. Some species that are on the Red List of Endangered Species were apparently able to settle in the naturally planted areas. The team even discovered the locust sand wasp (Sphex funerarius), which was believed to be extinct in Berlin and Brandenburg, on the median strip. The researchers made another unexpected discovery on Heerstrasse: There, the wild bee species Hylaeus intermedius was detected for the first time in Germany on the median strip.
Koch explains why the green areas between the traffic lanes were able to develop into such lively biotopes has to do with their isolated location in addition to the mix of plants: “Media strips are avoided by pedestrians and certain animals and have thus become protected habitats,” says the scientist. Apparently these living environments can cope with the pollution, the hot asphalt air in the summer and the road salt in the winter. However, other human sources of interference could be problematic, emphasizes Koch. He sees a danger for the median strip habitats primarily in the maintenance of the green strips: not only would excessive mowing deprive the insects of their food source, warns the entomologist, “the preferred abiotic factors such as temperature and humidity also change suddenly and light,” says Koch.
But as the MfN finally reports, Koch and his team have already won a victory for urban nature conservation in Berlin: They were able to persuade the green space authorities in the districts of Charlottenburg-Wilmersdorf, Friedrichshain-Kreuzberg and Treptow-Köpenick to only use median strips in the future to mow once a year.