Species and functional diversity of arthropod assemblages (Araneae, Carabidae, Heteroptera and Orthoptera) in grazed and mown salt grasslands

Grazing and mowing are widely applied management practices in semi-natural grasslands, which are one of the most important habitats for biodiversity conservation in Europe. Due to the decline in extensively grazing livestock numbers, an increasing area of formerly grazed grasslands has being used as mown grasslands. However, we have scarce information on how arthropod assemblages are influenced by mowing in formerly grazed pastures. We assessed the effects of mowing compared to grazing on the species richness, abundance and functional diversity of arthropods in three grassland complexes in Hungary. Since 2005, these salt grasslands have been divided into two management units: extensive grazing management has been continued in one part, while annual late cutting has been established in the other part. In each management unit five sites were sampled. Spiders and ground beetles were sampled using pitfall traps, orthopterans and true bugs were sampled using sweep nets twice before cutting in 2015. In total, the data relating to 12,576 adult individuals of 334 species were analysed using mixed-models. Plant-dwelling true bugs and orthopterans responded more sensitively to mowing than ground-dwelling spiders and ground beetles. Beside the general negative effect of mowing on the species richness and abundance of plant-dwelling arthropods, the shifts in the community weighted mean values of these assemblages suggested the importance of the body size, trophic behaviour and dispersal ability of species in the functional response of these assemblages to the different management regimes. Ground beetles and spiders were rather influenced by the differences in the moisture conditions and vegetation properties. Presumably, strong abiotic stressors such as drought can partly override management effects on ground-dwelling arthropods. The effect of uniform and simultaneous biomass removal on large areas, and the direct mortality caused by mowing was the most disadvantageous for plant-dwelling arthropods. Based on our results, traditional management practices should be prioritized in grassland conservation, as alternative management practices might be less effective in preserving grassland biodiversity.