Flowering fields, organic farming and edge habitats promote diversity of plants and arthropods on arable land.
Increased farming intensity led to massive declines across multiple farmland taxa. In Europe, measures introduced to counteract these losses include those considered agronomically productive, such as organic farming, as well as those that support no direct production of crops, such as non-crop flowering fields in conventional farming systems. We studied biodiversity effects of non-productive flowering fields managed under conventional farming compared to both an organically managed cereal mono-crop (organic winter spelt fields) and a flowering mixed-crop (organic lentil mixed-crop fields) as well as conventionally managed winter wheat fields, which served as control crop. These four crop-use types were studied on six sites over 3 years (17 sites in total) to assess their impact on the activity density (cover for plants), species richness and community composition of wild plants, carabids, spiders, butterflies and wild bees. Species richness of wild plants was highest under organic farming and at field edges when compared to the interior. In the case of carabids and spiders, species richness was highest at the field edges, but there was no difference between the four crop-use types. In contrast, activity density and species richness of butterflies and wild bees responded only to flowering crop-use types, showing no edge effects. Arable land cover in 500 m buffer area also affected community composition of all taxa, with the exception of spiders, but had only minor effects on activity densities and species richness. Synthesis and applications. Our findings underline that there is no single best measure to promote biodiversity on arable land. Instead a mosaic of non-productive and productive measures such as conventional flowering fields, organic crops and field edge habitats might be more appropriate to support the regional species pool in arable-dominated landscapes. To support a range of complementary biodiversity-promoting farming practices, agricultural policy should foster the coordination and collaboration between multiple farmers within the same region by covering additional costs for coordination and prioritizing collaborative schemes.