NEAFWA 2018

AUTHORS: Darin J. McNeil, Cornell University; E. L. Moser, Indiana University of Pennsylvania; Amanda D. Rodewald, Cornell University; Jeffrey L. Larkin, Indiana University of Pennsylvania and American Bird Conservancy

ABSTRACT: Bumble bees (Bombus spp.) play an essential ecological role within the northeast United States and beyond. Especially important for crops that require ‘buzz pollination,’ Bombus and other native bees are attributed with $3.07 billion per year in agricultural gross domestic product. However, like other bee species, Bombus are experiencing declines across the North American continent. These declines are thought to be driven by a variety of factors including pesticide use, exotic disease, and habitat loss. Though Bombus are relatively well-studied in agricultural systems, understanding of their ecology within native forest ecosystems remains almost entirely unknown. Moreover, the extent to which habitat management through silviculture benefits eastern bees remains unknown. To begin filling these knowledge gaps, we conducted an observational study across two heavily-forested counties of Pennsylvania (Clinton and Centre). In 2017, we conducted line transects through n=48 recently-managed forests, with each transect repeated three times. We then used hierarchical distance models to estimate detection probability and true Bombus density (bees/km2) as a function of habitat. We found that detection probability varied as a function of wind and density varied as a function of a variety of habitat features. Density models for habitat indicated selection for shrub cover but avoidance of sapling cover. Our interaction data suggested that Bombus relied mainly on flowering shrubs and herbaceous forbs during the sampling period. Dynamic patterns of habitat association appeared to be driven by plant bloom cycles with flowering shrubs selected most heavily during Vaccinium and mountain laurel (Kalmia latifolia) bloom and Rubus avoidance after its flowering period. Increasing densities of Bombus were recorded from period 1 (30.3 workers/ha) to periods 3 (127.5 workers/ha). Densities reported here are higher than the densities reported by many past studies highlighting the importance of early successional forests, and thus benefit of forest management, to pollinators like Bombus.