Response of bee pollinators to wildfire in sagebrush steppe

Great Basin rangelands have been severely degraded by human disturbances including excessive livestock grazing, the introduction of exotic and invasive grasses, and changing weather patterns. As a result, fire frequencies and intensities have increased dramatically during the past decades, perpetuating the downward ecological spiral of destructive fire and weeds. As part of a landscape-level approach to post-fire rehabilitation, land managers have been working to include native forbs in reseeding mixtures to increase habitat diversity and resist the spread of noxious weeds. Successful establishment of native forbs requires the presence of bee communities in post-fire habitats to provide pollination services. Understanding the response of bees to wildfire is therefore an important part of Great Basin rehabilitation efforts.

This study investigates the bee guilds sampled from a 15-year chronosequence of past large wildfire sites across sage-steppe habitats in the Great Basin. Paired plots were established far into the burn (>100 meters) and outside the burn to compare the following habitat characteristics: bee density in patches of target flowering hosts, the richness and similarity of bee communities; and the diversity, and density, of forbs and shrubs. Preliminary results indicate that any and all life stages of most cavity- and ground-nesting wild bees will escape injury from wildfire. Furthermore, in relatively mild burns of intact sage-steppe plant communities, entire bee communities exhibit excellent prospects for survival. However, where forbs do not bloom in the year following fire (especially in previously depauperate communities or hotter fires), surviving bee communities will need supplemental forage that blooms reliably the year after seeding.