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

Abstract

Summary1. 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. 2. 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. 3. Overall, uncropped margins sown with mixtures containing nectar and pollenproducing 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. 4. 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. 5. 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. 6. 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.

Invertebrates in field margins: taxonomic group diversity and functional group abundance in relation to age

“…Frequently established semi-natural areas on arable lands are field margin habitats (e.g., De Snoo 1999;Marshall and Moonen 2002). These margins can be beneficial to biodiversity in several ways: they serve as refuge habitats for species unable to persist in intensively managed arable fields or in the declining acreage of natural habitat (Vickery et al 2002;Marshall et al 2006;Carvell et al 2007;Smith et al 2008a), provide overwintering sites for a variety of small animals (e.g., Thomas et al 1992;Dennis et al 1994) and may act as ecological corridors (e.g., Kohler et al 2008).…”

The potential impact of global warming on the efficacy of field margins sown for the conservation of bumble-bees

“…Species added to a seed mix do not always provide significant amounts of bee forage, as evidenced by the fact that the wildflower mix contained 21 species, but only six of these predictably established themselves and were used as forage plants across all sites (other species established and flowered but were not always visited by bumble-bees) (Carvell et al 2007). Further trials are needed to determine which early-and lateflowering species will reliably flower under field margin conditions.…”

“…Flowering days were based on the first and last day in each year on which a species was producing 1-25 flowers per plot on at least four of the six study sites. Foraging bumble-bees were recorded in each field margin on repeated bi-monthly transect walks in each of the 3 years (Carvell et al 2007). Seven species of bumble-bee were recorded visiting flowers in the nectar flower mix, and eight species in the wildflower mix.…”

“…(a) Field sites and study species Field data on flowering phenology were collected over 3 years at six arable farm sites in central and eastern England for a study comparing five field margin management treatments with conventional cropping to the field edge in terms of their efficacy in providing forage supplies for bumble-bees (see Carvell et al 2007 for details of the field site selection, site locations and farm management). On each site, six experimental plots of 50 m by 6 m were established in September 2001 along two cereal field margins within the same field.…”

“…Once the management has been carried out, an annual subsidy is payable. Sowing 'nectar flower mixtures' in field margins has received relatively wide uptake in arable areas under Entry Level Stewardship (ELS) (Boatman et al 2007) and can provide a good forage supply for bumble-bees (Carvell et al 2007).…”