Response of beetles (Coleoptera) to repeated applications of prescribed fire and other fuel reduction techniques in the southern Appalachian Mountains

Coleoptera are important components of forest ecosystems and can be affected by forest management schemes aimed at limiting fuel build-up. Our research objective was to determine if repeated applications of fuel reduction treatments resulted in changes in abundance or diversity of beetle (Coleoptera) families, genera, and species within upland mixed hardwood forests in the southern Appalachians Mountains, North Carolina, USA. We established three replicate blocks (∼56 ha) and split each block into four fuel reduction treatments. Treatments included prescribed burning, mechanical felling, a combination of prescribed burning and mechanical felling, and a control (i.e., no fuel reduction techniques applied). We implemented treatments multiple times (2 mechanical thinnings and 4 prescribed burns) over the course of a 15-year period. Using pitfall and colored pan traps, we captured 7037 coleopterans comprised of 62 families over a three-year period. Total coleopteran abundance and diversity were similar across all treatments; however, some beetle families, genera, and species responded to treatments. Nitidulidae were significantly more abundant within controls compared to all other treatments in 2015, whereas Mordellidae generally had higher abundances in mechanical and burns compared to mechanical in 2015 and mechanical and controls in 2016. Chrysomelidae was significantly more abundant in mechanical and burns compared to all other treatments over the entire duration of the study. However, Staphylinidae abundance was significantly lower in mechanical and burns compared to the other treatments. Numerous genera and species also showed variable treatment-level responses. Burn treatments killed some mature trees and reduced forest canopy cover, resulting in higher light availability and thereby greater herbaceous cover and diversity on the forest floor. This vegetation in the understory of burned treatment units may be partially responsible for many of the treatment-level responses of beetle taxa we documented. This study took place after several rounds of fuel reduction techniques were applied over a 15 year period. Some beetle abundance responses were immediate; whereas other groups seemed to be influenced by the application of treatments over time, highlighting the need to examine long-term responses to forest management practices.