Comparing the efficacy of agri‐environment schemes to enhance bumble bee abundance and diversity on arable field margins

Abstract

Summary: Declines in abundance and diversity of bumble bees (Bombus spp.) in Europe have been linked to agricultural intensification and the resulting loss of suitable foraging and nesting habitats. Environmental Stewardship (ES) is a new scheme in England offering the opportunity to restore habitats of value for these important pollinators to agricultural land. Scientific evaluation of the options prescribed within the scheme is essential to ensure that their objectives are met and that the benefits can be realized by the full bumble bee species assemblage. We compared the efficacy of different ES options for field margins on arable land in enhancing the abundance and diversity of flowering resources and foraging bumble bees. Our study was conducted over 3 years using a multisite experiment. Overall, uncropped margins sown with mixtures containing nectar and pollen‐producing plants were more effective in providing bumble bee forage than margins sown with a grass mix, allowed to regenerate naturally or managed as conservation headlands. A mixture of agricultural legumes established quickly and attracted on average the highest total abundance and diversity of bumble bees, including the rare long‐tongued species Bombus ruderatus and Bombus muscorum. However, marked differences were observed between species and sexes in their responses to field margin management over time. A diverse mixture of native wildflowers attracted more of the shorter‐tongued Bombus spp. and provided greater continuity of forage resources, especially early in the season. Allowing Cirsium spp. to flower on such margins also increased their attractiveness to male bumble bees. Synthesis and applications. Our results suggest that the legume‐based ‘pollen and nectar flower mix’, as prescribed under Entry Level Stewardship in England, can quickly provide a highly attractive forage resource for bumble bees, but that issues of seasonal flowering phenology and longevity of the mixture need to be addressed. Establishment of ‘floristically enhanced margins’ under Higher Level Stewardship will be important to provide diverse perennial communities of forage plants and to support a greater range of Bombus spp. and other pollinators. The population‐level responses of bumble bees to introduced seed mixtures and other agri‐environment options require further study in order to maximize the benefits of such schemes in intensively farmed landscapes.