Fire effects on floral abundance of bumble bee host plants in mixed-oak forests

Abstract Background Pollinators are declining due to habitat loss, pesticides, and climate change. Fire may be an effective management tool for enhancing pollinator habitat in fire-maintained ecosystems. Many studies have demonstrated that fire can promote understory plant biodiversity and cover, but considerably less is known about the effects of fire on floral abundance and pollinators, particularly in mixed-oak forests of the eastern USA. Our goal was to assess the long-term effects of repeated prescribed fire on floral abundance and the abundance of bumble bees, a globally important group of pollinators, in mixed-oak forests. We hypothesized that repeated prescribed fire would increase floral abundance, particularly the abundance of bumble bee host plants. Results We sampled 22 vegetation plots in the Wayne National Forest, Ohio, USA, that were part of a fire experiment initiated in 1995 with three treatments: frequent fire, periodic fire, and no fire. To determine if fire treatment, plant cover, and environmental variables were related to floral abundance, we fitted generalized linear models with a negative binomial distribution, and then used model selection using AICc. Total floral abundance and floral abundance of bumble bee host plants were significantly higher in plots with repeated fire relative to unburned plots. Plant cover and soil texture were also significant predictors of floral abundance: plots with higher herbaceous plant cover and fine-textured soils generally had higher floral abundance. We detected a relatively small number of bumble bees, had low power to detect differences in bumble bee abundance, and this may be why bumble bee abundance was similar between the repeated fire and no fire plots. Conclusions These results suggest that prescribed fire enhanced floral abundance for bumble bees and potentially other pollinator groups in our mixed-oak forest plots and may be an effective tool for enhancing pollinator habitat. Additional studies are needed to characterize the effects of different fire regimes on bumble bees and pollinators more broadly in mixed-oak forests of the eastern USA.