Prescribed fire is associated with increased floral richness and promotes short-term increases in bee biodiversity in the ponderosa pine forest of the southern Rocky Mountains

Abstract

1. Managed low-severity surface fires are frequently implemented in efforts to restore disturbance processes to forests of North America; although the effects of managed fire on forest structure are well-studied, few studies investigate whether these disturbances cascade to impact pollinator communities. 2. We analysed bee-habitat relationships in fire-treated (1- and 3-years post-treatment) and non-treated ponderosa pine stands in Colorado to test wild bee population responses. 3. Observed bee richness and α-diversity were highest in stands 1-year post-fire and had more Anthophora, Bombus, Osmia and Lasioglossum spp. in comparison to 3-year postfire and non-treated stands. Bee functional groups were responsive to treatments, with more below-ground nesting taxa present in stands 3 years post-fire. 4. Floral richness was the highest mid-growing season (June, July) and within 1-year post-fire stands. 5. A model analysing the effects of foraging and nesting habitat variation on bee assemblages indicated positive association between floral richness and bee α-diversity, but negative relationships with stand basal area. Nesting habitat was not associated with variation in bee assemblages. 6. We conclude that managed fire has positive short-term effects on bee biodiversity that are likely mediated by floral richness. However, these effects were not detectable by 3 years post-treatment in the southern Rocky Mountain region.