PS 28-145 - Long-term effects of Fire Frequency on Floral Abundance and Bumblebee Abundance

Abstract: Pollinators are declining due to global climate change and habitat loss, caused by agricultural intensification and urbanization. In fire-adapted ecosystems, fire promotes plant biodiversity by reducing competition, and increasing light and nutrient availability. However, little is known regarding the effects of fire on Bombus (bumblebee) abundance and diversity, which are an important and well-known group of pollinators. This project will assess the long-term effects of fire on floral abundance, which Bombus require, and Bombus abundance and diversity. We hypothesized that sites with more frequent fire will have a higher abundance of floral resources and bumblebees. We conducted our study in the Wayne National Forest, OH, between May and September 2022. We chose the Wayne because of a well-documented fire history and known occurrences of plant taxa before and after fire treatments were initiated in 1995. Vegetation surveys were conducted by sampling 16 2 m² quadrats (32 m²) at 22 sites in three treatment areas that experienced different fire frequencies between 1995 and 2022: no fire, five fires (periodic), and seven fires (frequent). In all sites, all vascular plant species were identified, and all flowers, inflorescences, buds, and fruits were counted, excluding graminoids. We used linear models to evaluate differences in floral abundance between fire treatments. Non-lethal surveys of Bombus were conducted for one hour using a sweep net in the late morning. We found 240 unique plant taxa in our sites. Of those, 88 (37%) had reproductive structures. Mean floral abundance was 1.6 /m², 6.7 /m², and 6.0 /m² in the no fire, periodic, and frequent fire treatments, respectively. There was a significant difference in floral abundance in sites with periodic fire compared to sites with no fire (p = 0.048), and there was a marginal difference between sites with frequent fire and no fire (p = 0.09). We found that this trend was similar when we included fruits. Two Bombus species were observed in sites: B. impatiens and B. bimaculatus. However, a low number of individuals were observed and most surveys resulted in no bumblebee observations. Our results suggest that periodic fire has a positive effect on floral abundance, while sites without fire had considerably lower floral resources with potential negative effects on pollinators. Prescribed fire may be an effective tool for promoting the availability of floral resources with direct benefits to pollinator communities.