Low accuracy bark gouging controls Ips typographus outbreaks while conserving non-target beetle diversity

Natural disturbances and subsequent outbreaks of forest insects led to unprecedented amounts of damaged timber. In Eurasia, the European Spruce Bark Beetle (Ips typographus) breeding in Norway spruce (Picea abies) is creating the main share of infested trees in recent years. As alternative to salvage logging, different technics of mechanical and manual methods of bark removal for pest control are frequently applied in areas with conser- vation status or in protective forests that mitigate or prevent the impact of a natural hazard. To test the field applicability of bark removal technics, we compare work productivity mirroring economic costs between the widely used manual debarking and the new technique of bark gouging. Additionally, we evaluate how pest control and non-target biodiversity are affected from bark gouging if the phloem is cut with decreasing accuracy mirroring practical application by forest enterprises. Based on data of an experimental design we show, that bark gouging is twice as fast as manual debarking. From complete debarked P. abies logs no I. typographus emerged (pest control efficiency of 100%) but diversity of other emerging beetle species is reduced near zero. If bark gouging is conducted with high accuracy (phloem sufficiently cut in more than half of stripes) pest control ef- ficiency is 99.9% and for low accuracy (below 50%) pest control efficiency is still 95.7%. Non-target beetle diversity increases with reduced accuracy. Bark gouging combines sufficed pest control with biodiversity con- servation at lower work productivity than manual debarking and can thus be recommended for protected areas and protective forests, in particular.