Localised patterns of wild bee abundance indicate woodlands play multiple roles in supporting farmland populations

1. Higher woodland cover has been linked to increased wild bee abundance and diversity in temperate agricultural landscapes. However, our understanding of the roles played by the upper and lower strata of woodlands in supporting on-farm bees through spring and summer is lacking.
2. To explore these roles, we sampled bees (Anthophila) in deciduous woodland canopies and understories, and in an open habitat (at field margins), from May to July, at 12 sites across agricultural landscapes in Norfolk, England.
3. Before canopy closure in late spring, relative abundance in the two woodland habitats was generally higher, and canopies with flowering Acer pseudoplatanus L. supported more bees. However, throughout the season, open-habitat bee abundance was consistently higher closer to woodlands. After canopy closure, more open areas within woodlands were linked to greater bee abundance, except during a spike in temperatures when understory relative abundance was also at its highest.
4. These results indicate that deciduous woods on farmland provide floral resources to bees before canopy closure, which can be augmented with nectar-producing canopy trees. They also indicate that more open woodlands likely extend the availability of understory floral resources and that farmland woods, regardless of management, may continue to provide non-floral resources—including respite from hot weather—throughout the season.