Tradeoffs in longleaf pine conservation: Prescribed fire management increases exotic ambrosia beetle abundance in pine-hardwood forests

Abstract

Exotic woodboring insects, including some ambrosia beetles (Coleoptera: Curculionidae, Scolytinae, and Platypodidae), are threatening native forests worldwide. Longleaf pine (Pinus palustris Mill.) forest is an endangered habitat in the southeastern United States. One of the most important actions necessary for its conservation is prescribed fire, which maintains its savanna structure. However, prescribed fire is a forest disturbance, possibly creating new niches for colonization by exotic insects. The interaction between prescribed fire and exotic ambrosia species is understudied, especially in highly fire-dependent ecosystems. We carried out a two-year experiment in mixed longleaf pine forests in Alabama, USA. We compared ambrosia beetle communities in recently burned and unburned sites. We found that more than 66 % of total individuals in longleaf pine forests, regardless of fire management, were exotic species. Moreover, exotic ambrosia beetles were more abundant in burned stands, whereas native species showed no difference between burned or unburned stands. Fire management influenced stand species composition for native but not exotic ambrosia beetles. These results indicate that trade-offs exist in managing fire-dependent ecosystems, especially in the Anthropocene era, which is associated with rampant biological invasions. Fire is important to preserve the longleaf pine habitat, but it simultaneously acts as a disturbance, increasing the population density of those exotic species taking advantage of the presence of stressed or dying trees.