Trap log felling methods drive bark beetle communities without affecting Ips typographus (L.) densities on Norway spruce

Using trap logs to capture Ips typographus and control bark beetle infestations is a traditional forest management method in the hemiboreal region. However, the potential difference in effectiveness between trap logs felled by a chainsaw and those felled by a harvester in capturing bark beetles, particularly I. typographus, has not been investigated. Such differences may be caused by the variation in bark damage resulting from chainsaw versus feed rollers of the harvester head. A study was conducted where trap logs felled with a chainsaw and with a harvester were placed in small clearings created by sanitary cutting after infestations in the previous year by I. typographus– mimicking typical bark beetle control methods. Four weeks after the main flight period began, the number of live beetles were counted on bark samples from trap logs. There were no significant differences in capturing I. typographus depending on the felling method, but differences in accompanying bark beetle species were significant. The densities of Pityogenes chalcographus were greater on trap logs felled by chainsaw, but Polygraphus punctifrons and Crypturgus spp. occurred more likely on the harvester-felled trap logs. Species richness of bark beetles was greater on trap logs felled by harvester. Also, the sum of degree-days (cumulative thermal sum of daily maximum air temperatures above 8.3 °C) positively affected the densities of I. typographus beetles. To avoid re-emergence of mature beetles, frequent monitoring of brood development on trap logs is necessary.