Species-Enriched Grass-Clover Mixtures Can Promote Bumblebee Abundance Compared with Intensively Managed Conventional Pastures

Abstract

(1) Land use intensification has led to serious declines in biodiversity, including in forage production systems for dairy cows. Agri-environmental schemes, such as enriching grasslands in floral species, were shown to be an effective tool to promote biodiversity in higher trophic levels. Here, we studied an innovative pasture-based dairy production system with floral-species-enhanced temporary grasslands, with respect to the effect on wild bee abundance and species richness. (2) We studied three grass–clover mixtures with perennial ryegrass and clover species with different levels of plant diversity for flower cover and wild bees. The grass-clover pastures were rotationally stocked with cattle and parts of the pastures were excluded from grazing. Intensively managed conventional permanent grasslands were studied as the common land use type. Wild bees were caught by sweep netting. Wild bee diversity was analysed with a general linear mixed model. For species richness, an incidence-based coverage estimator was calculated. (3) In total, 541 wild bees from 10 species were found. No wild bees were caught on the conventional grasslands. Wild bee abundance and species richness did not differ among the three grass-clover mixtures, but with increasing flower cover of white clover (Trifolium repens), wild bee abundance increased. Except for one solitary wild bee individual, the recorded community exclusively consisted of bumblebees. While generalist species that are commonly found on farmland dominated, rare long-tongued bumblebees made up 10% on the grazed sites of the multispecies mixture and made up 20% on the ungrazed strips of the binary mixture and multispecies mixture. (4) We conclude that multispecies mixtures can provide resources for generalist bumblebee species, especially when compared with conventional grasslands that offer no resources. Considering that the multispecies mixture has been also shown to reduce greenhouse gas emissions and nitrate leaching, while maintaining high forage yields, our findings add to the potential to promote a wide range of ecosystem services. Yet, should their full potential be enfolded, grazing should partially be excluded, and the mixture should be extended by plant species with more open flowers, suitable for solitary wild bees.

Bees go up, flowers go down: Increased resource limitation from late spring to summer in agricultural landscapes

“…Increasing summer floral availability in pastures would likely require delayed or alternated mowing (Pywell et al., 2011) in order to extend the flowering period. Alternatively, legumes such as Trifolium repens , T. pratense and Medicago sativa , which are among the top 10 species contributing to July flower cover in our study area (Table S8), can be sown in pastures to benefit bumblebees (Baude et al., 2016; Beye et al., 2022). These recommendations can be applied to other pasture‐dominated landscapes, but as our landscapes largely do not contain mass‐flowering crops, these crops likely need to be taken into account in management strategies in arable‐dominated landscapes.…”

Improving pollen and nectar supply by identifying the red clover (Trifolium pratense) cultivars that attract most pollinators

“…Our study was carried out under management typical for silage production in the UK; however, further work looking at cultivars sown in a variety of seed mixtures is desirable. For example, inclusion of forbs in seed mixtures can support a greater diversity of pollinators (Beye et al, 2022; Brown et al, 2012; Woodcock et al, 2014), and identifying the best cultivars to include in diverse seed mixtures will be useful to farmers. Current initiatives aiming to reduce the negative impact of farming on the environment, such as the UK's Environmental Land Management Scheme (DEFRA, 2020) and the EU's European Green Deal (European Commission, 2019), are opportunities to better integrate pollinator‐friendly plant cultivars into farming.…”

“…Our study was carried out under management typical for silage production in the UK; however, further work looking at cultivars sown in a variety of seed mixtures is desirable. For example, inclusion of forbs in seed mixtures can support a greater diversity of pollinators (Beye et al, 2022;Brown et al, 2012;Woodcock et al, 2014), and identifying the best cultivars to include in diverse seed mixtures will be useful to farmers. Current tors (Carvell et al, 2006;Goulson et al, 2005;Rundlöf et al, 2014;Timberlake et al, 2020), optimizing benefits for both groups should be a priority for future research.…”

The importance of multi‐species grassland leys to enhance ecosystem services in crop rotations

“…Lavery et al, 2021)), or even eliminate it if designed to support a higher diversity of pollinators by including plants with different pollinator profiles in flower mixtures to enhance flower-visiting insects (Cong et al, 2020). In a comparison of grassland leys with increasing levels of diversity compared to a conventional monoculture of perennial ryegrass as permanent grassland, a study by Beye et al (2022) found that pollinator abundance increased drastically, with 541 wild bees of 10 species in the diverse grassland leys, compared to no wild bees in the permanent grassland due to the absence of flowers. Although pollinator abundance was not affected by the grassland ley diversity, the simple mixtures consisting of perennial ryegrass and white clover were only visited by common generalist species, whereas the multispecies grassland ley increased the abundance of rare long-tongued bumblebee to 10% in grazed areas, and even to 20% in ungrazed exclosures (Beye et al, 2022).…”