Agricultural intensification poses a major threat to the conservation of biodiversity and associated ecosystem services. Since non-crop habitats are regarded as important refuges for farmland biodiversity, various greening measures have been proposed to halt biodiversity loss. However, the effectiveness of these measures for biodiversity conservation is still under debate. Therefore, we here compared ground-dwelling beetle (Coleoptera) assemblages of different non-crop habitats (field margins, set-aside fields sown with wildflowers, and permanent grassland fallows) and wheat fields within an intensively used agricultural landscape in western Germany. Taxonomic diversity of Carabidae, Staphylinidae and other coleopteran families and their conservation value were higher in all non-crop habitats than on wheat fields. Surprisingly, though, different types of non-crop habitats did not differ in species richness or the number of threatened species. Thus, field margins and sown wildflower fields were as effective in promoting beetle diversity as grassland fallows. However, different non-crop habitats supported different species assemblages, and several species, in particular especially large ones, were restricted to grassland fallows. These results suggest that different greening measures are effective in promoting the biodiversity of beetles, and that permanent grassland fallows are essential for nature conservation. The fact that habitat types harbored different assemblages stresses the need to combine a variety of greening measures to yield the highest benefit for biodiversity.
1. 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.2. 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.3. 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.4. 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.5. 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.
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