Seed Mix and Prescribed Fire Impact Soil Conditions: Implications for Below-Ground Bee Nesting

Ground nesting bees comprise the majority of native bee species in the United States, yet their nesting ecology is poorly understood. Habitat restoration for native bees typically employs diverse wildflower seed mixes to provide floral resources without consideration of how these seed mixes might affect nest site availability. Ground nesting bees nest in a variety of microhabitats beneath or at the soil surface. We examined the effects of variation in seed mix type and prescribed fire on two variables generally considered to be important in nest site selection by ground nesting bees: soil temperature and moisture, both at the soil surface and at 11.5 cm depth. We collected data on soil temperature and moisture across 42 plots of a common garden experiment. We hypothesized that soil temperature and moisture are affected by seed mix density and amount of bare ground. We also hypothesized that fire affects microhabitat by making soil warmer and drier. Overall, we found no significant effect of seeding density on our dependent variables. Plots with more bare ground were drier at the surface than those with less bare ground. Burned plots were warmer and drier at the surface, but wetter and warmer at depth than unburned plots. Our results suggest that prescribed burns may play a large role in creating suitable nesting habitat for below-ground nesting bees. Our results highlight the need for greater understanding of the effects of plant communities and management on abiotic soil conditions that influence bee nesting conditions in prairie restorations.