Is grazing always the answer to grassland management for arthropod biodiversity? Lessons from a gravel pit restoration project

Abstract

Grazing by domestic stock is widely used in nature reserve management to maintain or restore characteristics of the flora. While the effects on plants are well understood, grazing effects on arthropods are in need of further investigation. We studied the effects of management on grassland arthropod communities at Needingworth, a mixture of grassland and wetland, created after gravel extraction. We hypothesised arthropod abundance and the species richness of Hemiptera and Coleoptera, would be no greater in fenced, ungrazed areas than in cattle-grazed grassland. We used suction sampling to collect grassland arthropods which were initially identified to order level, and then to species or genus level for the Coleoptera and Hemiptera. Abundance of total invertebrates and of all orders, except for Diptera, was greater in ungrazed than grazed grassland. We estimated that the presence of ungrazed grassland resulted in 14.9% greater invertebrate abundance at Needingworth. Community structure showed strong differences in relation to management, particularly in terms number of detritivores. Even the small amount of grassland management at Needingworth had distinct negative impacts arthropod abundance and community structure, and leaving ungrazed areas has the potential to benefit invertebrate biodiversity. We recommend that some grassland patches should remain unmanaged for long periods, as part of a mixed management strategy. Conservation grazing is not the only approach that should be used.