Floral richness drives pollinator diversity after fire in upland forests and meadows of the Sierra Nevada, California

Abstract

There are concerns over the effects of increasingly large and high‐severity fires that burn outside the local natural range of variation on ecosystem services and biodiversity. Pollinators provide important ecosystem services in the dry forests of the western United States where they depend on open habitat created or maintained by frequent, low‐ to moderate‐severity fire. We investigated the impact of burn severity on pollinator diversity in upland forest and meadow habitat at local (i.e., at the plot scale) and regional (burn severity class) spatial scales in the Sierra Nevada of California. In meadows, pollinator richness declined with increasing burn severity, but in uplands, there was no significant effect of burn severity on pollinator richness. Absence of pollinators was more likely to occur in unburned or high‐severity uplands. At the regional scale, we found that α was similar among burn classes in both habitats, although communities in burned uplands tended to be less even than unburned uplands. β was significantly higher in moderately burned than unburned upland habitat, but there were no significant differences in β for meadow habitats. Because meadows tend to be both more diverse and more sensitive to the negative impacts of high‐severity fire than uplands, conservation measures for pollinators could prioritise the removal of encroaching conifer species that may increase fire severity in these systems.