In the face of climate change, the European Spruce Bark Beetle (Ips typographus) breeding predominantly in Norway spruce (Picea abies) led to exceptional amounts of damaged timber in European forests. Up to now, if pest control is applied, damaged or weakened P. abies trees are either extracted by salvage logging or, when quantities are low, made unsuitable for breeding by manual debarking techniques. Both pest control interventions are costly, are often limited by the short timeframe of effectiveness and come with negative impacts on the non-target biodiversity. As alternatives for timely removal, a debarking head for harvesters for large scale disturbances and a bark gouging device for motor-manual treatment have been developed in recent years to make breeding material unsuitable for bark beetles and reduce existing larvae. Based on data from an experimental design with infested Norway spruce logs, we show that the harvester debarking head and the motor-manual bark gouging regulate I. typographus populations efficiently, whereas a conventional harvester did not reduce the emerging bark beetles. Species assemblages of non-target beetles living in the infested Norway spruce logs were altered from the natural species assemblages in control logs by processing logs with the debarking head or the bark gouging device but not by the conventional harvester. None of the bark treatments reduced non-target beetle species richness in this experiment. We endorse the debarking head and bark gouging as alternatives to salvage logging and manual debarking. This uncouples pest control from in-time dependencies on the availability of transport capacities. Further, the debarking head and bark gouging open up the opportunity to retain dead wood biomass in the forest, supporting ecological benefits and conservation goals. Particularly for protected areas these two new management option better balance requirements of pest control and biodiversity conservation.

The study was conducted in the buffer zone of the Bavarian Forest National Park, where active bark beetle interventions are implemented (N 49° 5' 13'' E 13° 14' 0''). Forest stands in this area are dominated by P. abies and have experienced extensive I. typographus outbreaks in the past. Sixteen P. abies trees of similar size, age and with signs of early colonization (white larval stage without teneral beetles) by I. typographus were felled in June 2020. All trees met the criteria for removal of the regulations for the buffer zone management and were randomly assigned in groups of four trees to each of the treatments, to account for potential differences in colonization densities between trees. The control trees were felled without any further bark manipulation. After felling, delimbing, and cutting into sections, the second group was treated with the bark gouging device attached on a conventional chainsaw (“Streifenmesser Nationalpark Bayerischer Wald”, EDER Maschinenbau GmbH, Wolfenbüttel, Lower Saxony, Germany). Another group of four trees was felled and processed with a harvester fitted with a conventional aggregate, representing the effect to logs from salvage logging and extraction operations. The last group was debarked using a John Deere 1270 G 8-wheel harvester in combination with a H 480 C debarking head, refitted with 4 debarking rolls and a Eucalyptus measuring wheel.The bark was completely removed by passing over the logs multiple times.

From each log, three segments, measuring 70 cm, were cut out at random locations to account for differences of colonization densities within the logs. Then, the 48 segments (12 per treatment) were placed in rearing barrels to collect abundances of all emerging arthropods from June until October 2020. All beetle species were separated from other arthropods and identified to species level by taxonomic expert Andreas Weigel.