Variation in prescribed fire and bison grazing supports multiple bee nesting groups in tallgrass prairie

Fire and grazing are historic ecosystem drivers of tallgrass prairie and both are used for restoration management today. The effects of these drivers on animal taxa are still incompletely resolved, especially for wild bees, a growing conservation and restoration priority. Fire and grazing could affect wild bee communities through structural changes to nest site availability via changes to soil conditions, vegetative cover, and availability of plant stems. Here, we sought to determine how different bee nesting groups are affected by the combination of fire and bison grazing management strategies. We grouped bee species by nesting substrate (ground, stem/hole, large cavity) because we expect the availability of these substrates to vary with the application of prescribed fire and grazing. We collected bees in restored and remnant high-quality tallgrass prairie and analyzed whether the proportion of each nesting group within the total bee community was predicted by fire and/or grazing. Ground-nesting bees reached their greatest proportion in bee communities immediately after prescribed fire, but declined proportionally over time since the last burn. Stem-/hole-nesting bees reached their highest proportion in the bee community with infrequent fire (6-year interval) and differed in their response to fire depending on the presence/absence of bison. Sampling year affected bee nesting groups and we found that nesting groups did not change in concert (i.e. different nesting groups had different good and bad years from each other). Our results show that spatiotemporal variation of prescribed fire and bison grazing is essential for conservation of multiple bee nesting groups.

Automated summary

This study investigated the impact of fire and bison grazing on different bee nesting groups, finding that the response of nesting groups varied depending on the substrate and management strategies. The results suggest that spatiotemporal variation in prescribed fire and grazing is crucial for the conservation of multiple bee nesting groups.