Disc Mower vs. Bar Mower: Evaluation of the direct effects of two common mowing techniques on the grassland arthropod fauna

In Central Europe, species-rich grasslands are threatened by intensive agriculture with frequent mowing, contributing to the reduction of arthropods such as insects and spiders. However, comprehensive and standardized studies on the direct effects of the two most agriculturally relevant mowing techniques, i.e., double-blade bar mower versus disc mower, are lacking. In a two-year experiment, we have investigated the direct effect of mowing on eight abundant arthropod groups in grassland, covering two seasonal mowing events in both years, using a randomized block design. We compared (a) an unmown control, (b) a double-blade bar mower, and (c) a disc mower. For most of the taxonomic groups studied, a significantly lower number of individuals was found in the experimental plots immediately after mowing, regardless of the mowing technique, compared to an unmown control. This was not the case for Orthoptera and Coleoptera, which did not show a significant reduction in the number of individuals for both mowing techniques (Orthoptera) or only for the double-blade bar mower (Coleoptera). Between both mowing techniques, no significant differences were found for all taxonomic groups investigated. Synthesis and applications. Our findings suggest that mowing in general has a negative impact on abundant arthropod groups in grassland, regardless of the method used. Tractor-driven double-blade bar mowers do not seem to be a truly insect-friendly alternative to a conventional disc mower. Other factors such as cutting height and mowing regimes should be seriously considered to protect spiders and insects from the negative effects of mowing. In addition, we highly recommend the maintenance of unmown refugial areas. Insects and spiders that are spared by mowing can take refuge in these unmown areas to avoid subsequent harvesting and thermally unfavourable conditions that arise on mown areas. Further, unmown refugia are basic habitat structures for a subsequent recolonisation of mown areas once the flora has recovered.