Bees in the woods: Spring orchard pollinators use forest canopy pollen

Pollinator communities are more abundant and diverse in agricultural matrices which include forests. These wooded habitats may provide resources in important early weeks of spring, after which time pollinators may “spill over” into crop fields. We sampled 2,885 springtime pollinators in nine apple orchards and their adjacent forest canopies and understories, and then with microscopy identified >340,000 pollen grains from the digestive tracts of those pan-trapped bees and flower flies. At each site, pollinator abundance peaked first in the forest understory, then in the forest canopy, and finally in the orchard. Pollinators ate large amounts of forest canopy pollen throughout the spring, especially prior to apple bloom. Bees had often eaten pollen from a different habitat than where they were caught, suggesting frequent cross-habitat movement. Male Andrena were primarily found in the woods but not the orchards where conspecific females were later active. We conclude that forested areas, particularly canopy trees, provide large amounts of early spring resources that facilitate spillover of wild pollinator populations into blooming orchards. Ecological forest management for wildlife can consider the groups of forest-associated bees which rely on forests for floral resources and nesting habitat.