Differential effects of fire regime and site conditions on bark beetles (Coleoptera: Curculionidae) in a longleaf pine (Pinus palustris Mill.) ecosystem

Abstract

Longleaf pine (Pinus palustris Mill.) ecosystems in the southeastern U.S. are fire-driven. Frequent prescribed fire or lack thereof through shifts in fire regimes may have consequences for tree health and associated herbivorous subcortical beetles (Coleoptera: Curculionidae). Yet, interactions between these ecologically and economically important beetles and prescribed fire in the southeastern U.S. are not well documented. We assessed the effects of various fire regimes, specifically of frequent fire, fire exclusion, and fire reintroduction, on bark and root-feeding beetles in mature longleaf pine stands in two edaphic types (mesic and xeric) in southwestern Georgia. We employed an information theoretic statistical approach to determine the effects of site conditions, as defined by both soil properties and stand structure, and prescribed burning on trap catches of subcortical beetles by species. We trapped a total of 141,611 beetles, indicating that subcortical beetles are abundant in this ecosystem. While the highest trap catches for three Ips beetle species were in the xeric fire-exclusion treatment, catches of I. grandicollis (Eichhoff) were similar at both sites for the fire-exclusion treatment. For the fire-exclusion treatment, I. avulsus (Eichhoff) and I. calligraphus (Germar) catches were 2–10 times higher at the xeric than mesic sites. Orthotomicus caelatus (Eichhoff) and Dendroctonus terebrans (Olivier) catches were 1.1–2.4 times higher in frequent-fire than fire-exclusion treatments. Root-feeding weevils, Pachylobius picivorus (Germar) and Hylobius pales (Herbst), exhibited opposite trends with catches higher and lower in burned treatments, respectively. Ips calligraphus were positively associated with percent basal area of understory trees, indicating this species may benefit from fire exclusion. Ips avulsus catches were negatively correlated with total basal area, suggesting this species may benefit from more open habitats like those facilitated by frequent fire. We conclude that both soil properties and stand conditions interact with the fire regime to differentially affect the catches of southeastern bark and root-feeding beetle species in a longleaf pine ecosystem.