Excess nitrogen puts butterflies at risk

In the journal Conservation Biology, the research team reports a connection between this unintentional fertilisation and the low diversity of butterflies in Switzerland.

Bern: Nitrogen from agriculture, vehicle emissions and industry is endangering butterflies in Switzerland. The element is deposited in the soil via the air and has an impact on vegetation- to the detriment of the butterflies, as researchers at the University of Basel have discovered.

In the journal Conservation Biology, the research team reports a connection between this unintentional fertilisation and the low diversity of butterflies in Switzerland.

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More than half of butterfly species in Switzerland are considered to be at risk or potentially at risk. Usually, the search for causes focuses on intensive agriculture, pesticide use and climate change. A research team led by Professor Valentin Amrhein from the University of Basel, however, has been investigating another factor- the depositing of nitrogen from agriculture and exhaust fumes from industry and traffic in soils via the air.

It was already known from previous studies that too much nitrogen leads to denser vegetation, but with a smaller selection of plant species.

Nitrogen stimulates the growth of less demanding plants in particular, with more specialised species being displaced. “We wanted to find out whether a nitrogen surplus also indirectly affects the diversity of butterflies via this change in vegetation,” explains Dr Tobias Roth, lead author of the study.

The team analysed data from Biodiversity Monitoring Switzerland on the diversity and prevalence of plants and butterflies on 383 plots throughout Switzerland. The result was clear: the more nitrogen introduced via the air to the areas studied, the less diverse the vegetation and hence the butterfly species.

“As caterpillars, some butterfly species need certain plant species as food, or are dependent on a certain microclimate,” Roth explains.