Reports of the “insect apocalypse” have led to a flurry of research not only on what harms pollinators, but what benefits them. A new study has come to the unexpected conclusion that, for all the problems of urban pollution, red clover pollination happens more reliably there than in agricultural zones. The findings reveal the role cities can play in promoting an insect recovery.
When metropolises expand it is usually a disaster for the environment, as fields and forests on their outskirts are covered in concrete and bitumen. Yet flowers grow in the cracks, and parks and gardens too. Dr Panagiotis Theodorou of Martin Luther University Halle-Wittenberg compared rates of pollination, and who is responsible.
Red clover plants in pots produced more seeds at locations inside nine German cities than counterparts in the countryside, indicating a higher level of pollination success. Using a combination of cameras to record all visits in 15-minute intervals, and pan traps, the researchers produced a record of the insects letting 1,000 flowers bloom.
As expected, rural areas had both more insects and much greater diversity. Flies and particularly butterflies remain relatively abundant there, despite the disturbing trends reported across Germany, compared to cities. Their pollination contribution is minor, however, at least of red clover.
On the other hand, Theodorou reports in Nature Communications, bumblebees do the heavy lifting when it comes to providing pollination services, accounting for three-quarters of pollination. Their greater urban abundance outweighs losses in all other insect orders. Counter-intuitive as the finding is, it follows the same team's similar observations for a single city four years ago.
Not only are bees more common in urban areas, at least in Germany, they're also more diverse, which Theodorou and co-authors attribute to the greater variety of nest sites. Wall cavities, for example, are beloved of bees and add to the dead wood and exposed soil found in both urban and rural areas. The range of flowers is probably also wider in many cities, where gardeners have differing tastes, compared to rural areas increasingly dominated by monoculture farming.
However, the authors also acknowledge cities may be safer places for bees simply because air pollution does them less harm than pesticides.
Maintaining urban pollination is important for reasons beyond wanting to beautify cities with flowers. "The number of urban vegetable gardens and orchards is also growing, but without pollinators, no fruit will ripen there,” Theodorou said in a statement. (Only one in eight flowering plants pollinate via the wind). Moreover, "If agricultural land degrades further, cities could serve as a source of pollinators for the farmland surrounding them.”
As a consequence, projects like London's proposed “bee corridor” and Utrecht's green-roofed bus shelters become even more valuable.