Grassland fallows as key for successful insect conservation

There is widescale evidence for declines in insect biodiversity at a global scale. Agricultural intensification is considered to be one of the major causes of these declines. Traditionally managed habitat types, such as hay meadows, harbour a rich diversity of plants and animals but have been often transformed into crop fields or silage grassland. To evaluate the role of (i) agricultural intensification for insect declines and of (ii) traditionally managed hay meadows and fallows for biodiversity conservation, we here compare bee, hoverfly, and leafhopper assemblages on 45 sites along a gradient of land use intensity in western Germany. We included moist long-term grassland fallows, three types of hay meadows, and silage grasslands, each represented by nine replicates. Species numbers of bees and leafhoppers were significantly higher on fallows than other management types. Grassland fallows also harboured the most distinct assemblages, while those of hay meadows and silage grassland were very similar and largely overlapping. The surprising similarity of hay meadow and silage assemblages may be due to investigating highly mobile taxa within a landscape composed of a fine-scale mosaic of traditionally managed and intensified grassland. Our results demonstrate the high importance of unmanaged areas, even when the overall land use intensity is still comparatively low. We suggest that temporal grassland fallows (unmanaged for 3-5 years) should be subsidised in agri-environmental schemes to increase landscape heterogeneity and to preserve insect diversity.

Automated summary

The study found that grassland fallows and hay meadows play a crucial role in maintaining insect numbers and diversity, suggesting that temporal grassland fallows should be subsidized in agri-environmental schemes to enhance landscape heterogeneity and preserve insect diversity.