Early spring orchard pollinators spill over from resource-rich adjacent forest patches

Pollinator communities are more abundant and diverse in agricultural matrices with more natural habitats, although the reasons for these correlations remain unclear. It is possible that forest fragments and edges provide resources for pollinators in the important early weeks of spring, after which time those insects can then “spill over” into crops such as apple orchards during bloom.
To explore how forest edges may feed and therefore promote flower visitor communities in adjacent agricultural habitats, we sampled springtime pollinators in nine orchards and their adjacent forest edge canopies and understories. We identified pollen consumed by pan-trapped bees and flower flies to assess if bees ate pollen where they were caught and if their diets similarly “spill over” from forest to orchard. We further explored sex differences in habitat usage.
Our spatially replicated sampling found that bee and flower fly abundance peaks first in the forest understory, then in the forest canopy, and f..., Bee and flower fly collection: This study was completed in the Finger Lakes region of New York, in the northeastern United States. Bees and flower flies (Syrphidae), two major groups of agricultural pollinators (Rader et al., 2016) were collected in nine second-growth deciduous forest patches that were selected for their adjacency to orchards. The most abundant tree species across sites were Acer saccharum, Acer rubrum, Quercus rubra, Fagus sylvatica, and Betula spp. Several sites also had Tilia americana, Populus deltoides, Juglans nigra, Carya ovata, or Carya cordiformis (see percent basal area at each site in Supplemental Figure A1). For simplicity, we will refer to bees and flower flies as “pollinators” hereafter. For full forest sampling methods, see Urban-Mead et al., (2021). Briefly, five paired canopy and understory pan traps in sets of vertically randomized blue, yellow, and white were deployed in canopy-dominant trees in second-growth forests and woodlots beginning in mid-Marc...,