It’s not every day that mining wins acclaim for its ecological benefits. But a new study suggests rock quarries in northern Germany have become wildlife refuges for Europe’s silver-studded blue butterfly, whose meadow habitat has been in severe decline for the past 100 years.
“It’s a bit unusual that quarries are a good thing,” muses Martin Warren, an ecologist at Butterfly Conservation Europe, who was not part of the research. The discovery is emblematic of the problems facing butterflies across Central and Western Europe—and it’s an argument to keep limestone quarries operational, some scientists say.
Half of Europe’s butterfly species are found in grasslands with soil made alkaline by limestone or chalk. Away from the shade of forests, insect larvae flourish in higher temperatures and feed on plants found in the sunny fields. The silver-studded blue (Plebejus argus) is one of these: It lays a single egg at a time in low-to-the-ground flowering vegetation, and its offspring are guarded by the cornfield ant, which feeds on a sticky substance excreted by the caterpillar.
In the distant past, roaming herds of grazing animals like the now-extinct aurochs are thought to have kept trees away from such meadows. More recently, domesticated livestock took over that role. But the decline of traditional herding and the resurgence of forests in the second half of the 20th century have reduced meadows by as much as 90% in Western and Central Europe, and many butterfly species have dwindled with them. The silver-studded blue saw populations cut by more than half in parts of northern Europe and the United Kingdom.
To find the silver-studded blue’s remaining refuges in northern Germany, ecologist Thorsten Münsch spent two summers scouring the Diemel Valley and the Brilon Plateau, home to the region’s largest concentration of alkaline grasslands in north Germany. The Osnabrück University Ph.D. student looked in abandoned and managed meadows and quarries, where the butterflies had been spotted in the past.
Butterflies were thriving at all nine of the active quarries Münsch visited, apparently unperturbed by the mining activity nearby. Twelve abandoned quarries, or 60%, had the butterflies as well. But only 57% of actively managed meadows were home to the silver-studded blue; abandoned meadows did not have them at all. The number of butterflies in active quarries was four times higher than in comparable-size grasslands, the researchers report this month in Insect Conservation and Diversity. Perhaps the species should be renamed “quarry blue,” quips Mnsch’s supervisor, ecologist Thomas Fartmann, who has spent the past 2 decades tracking insects in the region.
The butterfly may thrive in active quarries because its egg-laying plant of choice, birdsfoot trefoil, grows well in the parts that aren’t being excavated, Fartmann says. The thin soil and recent disturbance likely keep other, bigger plants from growing there and outcompeting it, he adds. Quarry temperatures are also higher than in abandoned meadows, where a lack of grazing means more vegetation—and shade.
Dirk Maes, a conservation entomologist at Belgium’s Research Institute for Nature and Forest, has witnessed something similar: Hills of rubble from the coal mines that once dotted the Belgian landscape are now home to another meadow-loving butterfly, the grayling (Hipparchia semele). With their thin soils and sparse vegetation, mine waste is more hospitable than the butterflies’ usual heather-covered habitat that has been transformed in recent years by the loss of grazing and the addition of nitrogen to the soil from fertilizer and fossil fuel combustion, which in turn fuels the growth of bushes and trees.
The findings suggest some butterflies benefit from more human activity, not less. To support the insects, limestone quarries could be kept open, Münsch says, and shrubs could be cleared from defunct ones. Sheep and goats could be deployed to keep grasslands open and fires could be used to keep bushes at bay. People riding mountain bikes or horses can provide some of the same benefits, Maes says. He recently urged land managers in Belgium not to close an abandoned railway to recreation for just that reason. “They didn’t listen to me,” he says.
Warren says paying farmers to create or protect ecologically valuable meadow habitat is the most promising strategy. Industrial mining can also destroy sensitive habitat and create landscapes where very little grows, he cautions. “I don’t think you should get across that all quarries are good,” he says. “They’re not.”
Source: Science Mag