Arthropod conservation in roadside verges: Unmown refuges outperform mowing equipment changes

Abstract

Roadside verges can provide habitats and serve as stepping stones for grassland arthropods. However, they are often subject to intensive mowing, often beyond what is necessary for road safety and maintenance. While traffic-related mortality and habitat isolation by road surfaces are inherent characteristics of roadside verges, different mowing techniques or strategies could support insects relying on this habitat type by increasing habitat quality. The present study compared the direct influence of three different mowers on arthropod densities, composition and species richness in roadside verges: a conventional roadside flail mulcher, a roadside ‘eco mower’ and a string trimmer. Additionally, we sampled an unmown area directly adjacent to each mown area to study the impact of refuges and of including a scare device in front of the ‘eco mower’. Our results indicate a generally negative impact of all three mowing techniques on arthropod densities, but no statistically significant differences in the log response ratio (LRR: before and after mowing) of arthropod densities between the techniques. Arthropod densities in refuges remained unchanged from before mowing, indicating that unmown refuges provided essential habitat during the mowing process. The scare device mounted on the eco mower did not increase the number of arthropods fleeing to an unmown refuge. The mowing treatments had little effect on the community composition of arthropods, and species richness was partly affected by mower types, indicating that direct mowing impacts mostly affect arthropod abundance. Synthesis and applications: Regardless of mower type, unmown roadside refuges play a crucial role in mitigating the overall negative effects of mowing on arthropods and serve as habitats in a hostile environment.