Biodiversity strengthens pollinators and ensures stable yields

For their study, researchers from the University of Würzburg (JMU), together with the Bavarian State Institute for Agriculture, analysed 29 sunflower fields in northern Bavaria – 15 organically and 14 conventionally farmed. They wanted to know which factors influence wild pollinators and how this affects agricultural yields. They took into account both the conditions in individual fields and the structure of the surrounding landscape.

To determine the contribution of insects, they used a simple experiment: some sunflower heads were protected from pollinators with fine nets, others were left open. The result: On average, freely pollinated sunflowers achieved around 25 per cent higher yields - regardless of whether they were grown on organically or conventionally farmed fields.

Different Requirements, Common Benefits

The analysis showed clear differences between different pollinator groups: "Bumblebees, for example, benefited from a high proportion of organically farmed fields," explains Denise Bertleff, first author of the study and biologist at the Department of Animal Ecology. "We were able to show that If you increase the proportion of such areas from 10 to 20 per cent, this almost doubles the bumblebee population."

The abundance of solitary bees, on the other hand, is based on the size of semi-natural habitats such as hedges, calcareous grasslands or orchards. "Our study shows that agriculture can be organised in a way that promotes biodiversity," says Bertleff. "A diverse landscape, for example by deliberately leaving weeds standing, makes harvests more stable and safeguards biodiversity."

Study Provides Recommendations for Practical Action

The researchers used their data to derive several recommendations for action for farmers, policy-makers and nature conservation advisors:

• Manage more land in a region organically: This strengthens the number of pollinators – even on conventional fields.
• Preserve semi-natural habitats such as hedges, calcareous grasslands and orchards: Such areas are essential for pollinators, especially for solitary bees.
• Allow moderate amounts of weeds: They provide important food sources for wild bees and hoverflies without necessarily reducing yields.
• Avoid excessively large flowering areas: If too many crops flower in one area at the same time, there is a risk of dilution effects because pollinators are spread over larger areas. This can reduce pollination performance in individual fields.

The project was funded by the Federal Ministry of Food and Agriculture (BMEL) on the basis of a resolution passed by the German Bundestag. The project was organised by the Federal Office for Agriculture and Food (BLE).

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