Variable effects of organic farming systems on ground beetle abundance and diversity

Summary

Organic farming should support high levels of biodiversity and rely on biological pest control by natural enemies. Management of organic systems must comply with specific regulations, but within this frame management is not clearly defined. In experimental cabbage fields we studied ground beetle abundance and diversity in three different organic farming systems (O1, O2, and O3). All systems complied with regulations for organic production, but relied on either high (O1) or low (O2 and O3) external input of nutrients. The systems O2 and O3 also included green manures, and in O3 strips of green manure were left between crop rows. A conventional system was included as control. Only organic systems O2 and O3 showed benefits for ground beetles, but in different ways. Abundance of all ground beetle species was highest in May in O2, while O3 supported the highest abundance of habitat specialists with preferences for field margins reflecting the conservation of green manure strips. The ground beetle community of O3 was most diverse characterized by highest number of species and evenness (equitability among species). Organically farmed fields can therefore be designed to promote specific predators or high ground beetle diversity at the field scale by implementing different management practices.