Response of bark beetles and woodborers to tornado damage and subsequent salvage logging in northern coniferous forests of Maine, USA

In July 2013, an EF1 tornado and straight line winds caused extensive forest damage in the Scientific Forest Management Area of Baxter State Park in northern Maine, USA. Subsequent salvage operations removed damaged trees from some areas, while leaving blowdown in other areas. Undisturbed control, blowdown, and blowdown + salvage (hereafter, salvage) treatments were established within and adjacent to damaged forests. Bark beetles (Coleoptera: Curculionidae: Scolytinae) and woodborers (Coleoptera: Buprestidae, Cerambycidae; Hymenoptera: Siricidae) were trapped using semiochemical-baited traps from within each of these areas over a three-year period (2014-2016). Disturbance-initiated outbreaks of Dendroctonus rufipennis were a major concern after the windstorm. However, D. rufipennis populations were low throughout the three-year experiment, and were captured more often in controls than in the two disturbed treatments. Overall, bark beetles and woodborers were captured at higher numbers in the two disturbed treatments, relative to controls. Individual species responses varied, with many species found more often in one of the disturbed treatments compared to controls. Species richness and abundance were generally higher in disturbed treatments than in controls. Slowdown and salvage treatments were also more similar to one another than to controls. Large amounts of dead wood provided easily exploitable habitat for wood-inhabiting insects in treatments; however, no evidence of alarming population increases of primary bark beetles were observed, suggesting that salvage operations are not always necessary to protect residual trees from attack by damaging bark beetles.