Effects of fire and thinning disturbance on biodiversity of wild bee communities within the Colorado Front Range

Forest restoration goals within Colorado’s lower-montane forests align with conservationists’ goals of creating desirable habitat for bees through improving habitat connectivity and herbaceous production, though current knowledge of how forest management impacts bee communities is limited. In this project, blue vane traps were used to sample native bee community assemblages across the growing season within 39 ponderosa pine forest sites in central-Colorado to assess effects of fire and forest thinning disturbances on bee populations. We quantified bee abundance, richness, and diversity as well as floral resources (abundance, richness) and nesting habitat (woody debris) to understand factors that predict bee distributions.  Four key findings emerged: (1) Overall γ-diversity was high and consisted of 4 families, 20 genera, and 57 unique species. (2) Bee abundance did not vary due to effects of thinning or fire, though species richness was highest at sites that experienced high-severity fire. (3) Floral resources were positively-correlated with bee abundance and species richness, and woody debris was positively-correlated with bee species richness. (4) Bee community composition varied across disturbance types, with ~40% of genera found in specific habitats. We conclude that forest thinning operations are not associated with reductions in bee abundances or species richness, and fire disturbances generate foraging and nesting habitats important for native bee diversity. However, community structure varied across disturbance types and specific assemblages were associated with non-treated, thinned, and burned sites, indicating that managers can use thinning and burning treatments as tools for conserving bee biodiversity on the landscape.