Fallows benefit beetle conservation in a traditionally managed grassland landscape

Insect biodiversity is declining at the global scale, with agricultural intensification representing a major driver of this development. Traditionally managed grassland, such as hay meadows, can support high insect and plant diversity but is often converted into more productive cropland or silage grassland. We evaluated the effects of agricultural intensification and conservation measures on beetle assemblages in a traditional landscape dominated by grassland in western Germany. We investigated a total of 45 grassland sites including long-term (abandoned) grassland fallows with natural vegetation cover, three types of hay meadows, and intensively used silage grassland, using different sampling methods targeting ground-dwelling, flower-visiting, and vegetation-dwelling beetles. Species richness and diversity were highest on grassland fallows, while variation among different types of managed grassland was very low. Thus, fallows outperformed even unfertilised hay meadows cut after July 15th in terms of species richness. Beetle assemblages of fallows and silage grassland were both distinct from all other management regimes, while the three types of hay meadows did not differ substantially. Effects of on-site management regime were strong, but environmental parameters and surrounding land cover were of minor importance only. Our results suggest that long-term fallows are important for beetle conservation, even in landscapes with overall low land-use intensity. We suggest that grassland fallows should be considered in subsidised agri-environmental schemes.