D3336: The influences of forest structure on the vertical distribution of native bees and resource availability

Recent research suggests that native bee communities are distributed throughout the vertical strata of temperate forests. Some studies have identified unique assemblages between, for instance, canopy and understory strata across seasons. Yet the inherent variability of canopy height and interior structure among forest types has led to inconsistent interpretations of bee community responses at different heights from the forest floor. It follows that there is growing evidence of a diverse subset of bees occupying the forest space above our heads, but little evidence supporting specific mechanisms as to why they are there. We addressed these issues by analyzing a dataset of 4,770 bees sampled at 1, 6, 11, and 16 meters above the forest floor, as well as 21 and 26 meters in higher canopies, at 47 sites across nine forests in western Massachusetts, USA that varied in composition and structure. Our findings demonstrate that relative canopy height is a better predictor than absolute height for fitting models of bee community responses across the vertical gradient of temperate forests. We also show how food and nesting resource availability, including flowers and dead wood, throughout the vertical gradient of the canopy interact with the bee community and its seasonal turnover while investigating the roles of edge effects of adjacent openings 0 – 620 meters away. Our study serves as a jumping-off point for other forest-bee researchers as we discuss more species-specific trends and potential bee-tree relationships.