The α and β-diversity of native bees is driven by disturbance-mediated shifts in stand structure, floral resources, and nesting substrate in a southwestern ponderosa pine forest

Using blue vane traps, bee community assemblages were sampled across the growing season in 39 ponderosa pine forest sites in central Colorado to evaluate the effects of wildfire and forest thinning disturbances on native bee populations. We quantified bee abundance, richness, and diversity as well as foraging resources (flower abundance and richness) and nesting habitat (woody material). Three key findings emerged: (1) overall γ-diversity was high and consisted of 5 families (Andrenidae, Apidae, Colletidae, Halictidae, and Megachilidae), 30 genera, and at least 70 unique bee species. Predominant genera consisted of bumblebees (Bombus spp.) and mason bees (Osmia spp.) accounting for 50.5% and 9.2% of all captures, respectively. (2) Average bee abundance did not vary across disturbance types, though bee species richness and α-diversity were highest in stand affected by high-severity wildfire. (3) Bee assemblages were different across disturbance type, such that bee biodiversity was highest in high-severity wildfire stands. We conclude that thinning operations are not associated with reductions in bee abundances, richness, or diversity, and fire disturbances generate foraging and nesting habitats that are important for native bee diversity. However, community structures vary across disturbance types and specific assemblages tend to be associated with non-treated, thinned, and burned sites, indicating that managers can use thinning and burning treatments as tools for conserving bee biodiversity across the landscape.