Four-dimensional use of forests: Investigating local bee-forest associations throughout the season within and above the canopy

The body of literature addressing and supporting vertical stratification of native bee communities within temperate forests is growing rapidly. Yet the structural complexity and variability within and among forests makes it difficult to conclude generalized patterns of how bees are distributed in relation to the local availability of forest resources. We sampled the bee community throughout the active seasons of 2020 and 2021 up to 26 meters into forest canopies of the Pioneer Valley in western Massachusetts at a total of 37 vertical transects. We recorded properties of the forest structure and composition, as well as availability of nesting resources within 11.3 meters of each transect, and additionally quantified floral resources in 2021. We discuss how relationships between the bee community and these local properties of the forest interior changed throughout the season along a vertical gradient. Our findings highlight some unanticipated associations in the high canopy, which resulted in a small follow-up study throughout 2021 that compared bee assemblages above the forest canopy with those of strata below the forest ceiling. Collectively, our studies provide a novel understanding of how the structure of forests influences local forest-bee associations, while also revealing an abundant and diverse assemblage of the forest-bee community in a previously unexplored stratum – the canopy-aerosphere interface – that needs further investigation in our quest to understand the extent of ecological importance of temperate forests for native bees.