Therapeutic Bark Gouging as an Effective Complement for the Management of <i>Ips typographus</i> and <i>Pityogenes chalcographus</i> While Preserving Habitat for Secondary Scolytine (Coleoptera: Curculionidae) Species

ABSTRACT Norway spruce will likely remain an important tree species in Europe over the next few decades despite efforts to transform forests and reduce its distribution range more to its natural range. Consequently, Ips typographus will remain one of the most relevant forest pests the management of which will become increasingly challenging due to changing environmental conditions. When salvage and sanitation logging are not feasible, alternative preventive and control measures are established, including mechanical debarking. Alternatively, partial removal of bark, for example through bark gouging, offers a compromise between deadwood retention for conservation purposes and bark beetle management. The preventive use of bark gouging has been documented and previous results suggest that also the therapeutic use is effective. However, it was not clear how the treatment success depends on the timing of the treatment during the development of I. typographus and how it relates to the colonisation density. This was investigated in a 2 year experimental series in south‐east Germany. Bark gouging at all tested time points (during oviposition, late larval stage, pupation) significantly reduced the reproductive success of I. typographus . Yet, the efficacy decreased over time, suggesting that the treatment should be carried out as early as possible in practice. Due to the unplanned co‐colonisation of other species, we could show for the first time that the reproductive success of the much smaller Pityogenes chalcographus is also significantly reduced. The effect on the abundance of two secondary species, Dryocoetes autographus and Hylurgops palliatus , was more variable. The richness of non‐target scolytine species was not affected, emphasising the benefits of bark gouging for nature conservation. We consider bark gouging as a simple, low‐cost alternative to conventional measures for small amounts of damaged wood, which allows to relax logistical constraints in bark beetle management and reconcile diverging management objectives.