The effects of repeated prescribed fire and thinning on bees, wasps, and other flower visitors in the understory and midstory of a temperate forest in North Carolina

Abstract

We investigated the effects of repeated prescribed fire, mechanical thinning, and combinations of fire and mechanical thinning on pollinators and flower visitors within the herbaceous understory and midstory of a temperate forest in North Carolina. Using colored pan traps, we sampled flower visitors during the plant growing season between 2014 and 2016. We captured 5,520 flower visitors that were dominated by halictid bees and vespid wasps. Twenty genera of bees representing at least 30 species were captured within our experimental plots. Within the forest understory, we found higher abundances and diversities of bees and other flower visitors within plots that had been treated with prescribed fire or a combination of mechanical thinning and prescribed fire compared to control plots. Within our midstory samples, we found that forest management practices did not affect the abundance of any common flower visitor species/family. However, Augochlora pura and Vespula spp. were more abundant in the midstory compared to the forest understory. Overall, our study demonstrates that repeated applications of prescribed fire maintained elevated abundances and diversity of bees and other flower-visiting insects compared to untreated plots, likely due to increased herbaceous plant diversity and enhanced quality of nesting habitat within the understory. Our results also indicate that many flower visitors utilize the midstory of a temperate forest potentially for foraging habitat.