Canopy cover and seasonality are associated with variation in native bee assemblages across a mixed pine-juniper woodland

Pollinator community responses to changing conditions are a concern for ecosystem managers, but it remains poorly understood how shifts in forest structure impact pollinators across small scales. To address this, bee assemblages were sampled in arid woodland habitat in the southwestern United States (Colorado) to evaluate effects of canopy cover and seasonality on bee diversity and composition. >2500 specimens were captured representing 5 families and 30 genera. Bee composition shifted seasonally; early-season assemblages were predominated by Halictidae (Lasioglossum and Halictus); late-season assemblages were predominated by Apidae. More bees were captured in canopy gaps early-season, but differences due to canopy openness declined by late-season. Bee diversity was higher in open-canopy sites and bee assemblage composition varied across canopy openness. Low cover was positively associated with large-bodied bees and negatively associated with solitary, polylectic ground-nesting bees. Parasitic bee taxa were more abundant when the canopy was composed of pinyon pine; ponderosa pine-dominant canopies were associated with large-bodied bees with variable nesting habits. We conclude that canopy cover and seasonality both predict abundance and diversity of bee assemblages in arid woodlands, and bee functional traits are responsive to canopy cover and dominant overstory species across small spatial scales.