Association between severity of prescribed burns and subsequent activity of conifer-infesting beetles in stands of longleaf pine
A randomized complete block experiment was performed to measure the effect of prescribed, dormant-season burns of three different levels of severity (measured as fuel consumption and soil surface heating) on subsequent insect infestation and mortality of mature longleaf pine (Pinus palustris Mill.). Multiple-funnel traps baited with a low release rate of turpentine and ethanol were used to monitor activity of certain coniferophagous beetles. Non-aggressive species, including the root beetles Hylastes salebrosus Eichhoff and H. tenuis Eichhoff, the ambrosia beetle Xyleborus pubescens Zimmermann, the reproduction weevil Pachylobius picivorus (Germar), and buprestid borers, were attracted to burned plots in numbers that correlated positively with burn severity. Beetle attraction to burned sites was greatest in the first weeks post-burn and disappeared by the second year. Two potential tree-killing bark beetles, Dendroctonus terebrans (Olivier) and Ips grandicollis (Eichhoff), were trapped in significant numbers but exhibited no attraction to burned plots. Tree mortality correlated significantly with the severity of the burns and amounted to 5% of stems in the hottest burn treatment after 3 years. The majority of the mortality was observed in the second and third years post-burn. Attacks of Ips and Dendroctonus bark beetles were apparent on nearly all dead or dying trees, and evidence suggested that root pathogens may have contributed to tree susceptibility to beetle attack and mortality. Our data indicate that selection of burn regimes that reduce or eliminate consumption of duff (e.g., favoring heading fires over backing fires) could significantly reduce mortality of longleaf pine managed for long rotations.