Functional traits and nesting habitats distinguish the structure of bee communities in clearcut and managed hardwood & pine forests in Southeastern USA

Abstract

The role of nesting resources has been largely neglected in wild bee community ecology studies. Anthropogenic forest openings such as clearcuts and roads are common features within the managed forest matrix which may have varying impacts on bee nesting habitats and thus, drive their community structure. We sampled wild bees in mature hardwood, managed pine, and regenerating clearcuts across a gradient from the edge of a road into each site-type. Each site was surveyed for nesting habitat indicators including depth of duff layer, volume of downed wood, decay class of downed wood, and number of snags. Regenerating clearcuts had higher alpha diversity of wild bees than other sites, but displayed higher functional overlap in the bee community, favoring soil nesting groups. Forested sites, especially hardwoods provided more nesting niche opportunities leading to higher functional dispersion, evenness and higher beta diversity, and supported more cavity nesting, softwood nesting, solitary, and early season bees. Nesting habitat indicators explained 53% of the variation in nest guild composition. Cavity nesting bees responded positively to the volume of downed wood, and in a bimodal way to woody decay class. Soil nesting bees responded negatively to the depth of duff layer and presence of snags. Overall, results indicate that regenerating clearcuts are foci of species diversity, while hardwood forests are foci of functional diversity. Hardwood forests may be source of functionally diverse groups of bees, and maintaining patches or swaths of hardwood forests with some downed wood accumulation may be critical for maintaining functional diversity of bees in managed forested ecosystems.