Effects of roadside habitat management on epigeic arthropod diversity: a case study from the Nitra-Selenec expressway...

Linear transport infrastructure fragments habitats, but its edges can serve as significant refuges for invertebrates. Management of these verges is crucial to realise this conservation potential, but the impact of specific habitat measures on epigeic arthropods remains poorly understood. This study assessed the impact of roadside habitat management on the diversity and composition of epigeic arthropods, using ground beetles (Carabidae) and harvestmen (Opiliones) as bioindicators at the Nitra-Selenec expressway junction, Slovakia. Over two years, we used pitfall traps to sample epigeic arthropods at ten sites managed under three different regimes: passive management (no intervention), active management with renewal/seeding (commercial grass-herb mixture), and active management with mulching only. We analysed the influence of management, vegetation structure, and landscape variables on species assemblages using redundancy analysis and predicted population trends using machine learning. We recorded 1,416 carabids (50 species) and 1,409 harvestmen (6 species). The renewal/seeding intervention had a significant negative effect on the community composition. The structure of the vegetation, specifically the cover of the herb layer and species richness of the shrub layer, were the most significant positive drivers of community assembly. Furthermore, distance from the road significantly influenced species distribution. Analysis of population trends revealed a gradual increase in carabid abundance over time, but an alarming decline in harvestmen. Active revegetation with commercial seed mixtures creates a homogeneous habitat that is less suitable for diverse epigeic communities than passive management. The structural complexity provided by various native vegetation is a key factor in supporting invertebrates. Implications for insect conservation: We recommend that roadside managers prioritise passive management or regionally appropriate native seed mixtures over commercial revegetation, maintain structural complexity of vegetation through a reduced frequency of mowing (1-2 times annually at ≥ 10 cm height), and adopt mosaic approaches that combine intensive mowing only in safety-critical zones with extensive management elsewhere.