Competing or commensal species? On the occurrence of bark beetles in upper montane coniferous forests in Central Europe

In the upper montane zone of coniferous forests in the norther part of the Karkonosze (Giant) Mts. analyses were conducted on the colonisation of spruce trees by bark beetles (Scolytinae, Coleoptera), providing data on the species composition of the assemblages and the frequency of individual species. The study was conducted in 2020–2021. Twenty-four trees (144 sections) were inspected. Thus, the frequency of Ips typographus, I. amitinus and Pityogenes chalcographus was determined in trees colonised in the spring and summer periods. Preferences of these spruce bark beetle species were specified in relation to the colonisation of individual stem sections of specific thickness. It was found that the share of Ips amitinus in the assemblage of bark beetles in spruce coniferous forests in the upper montane zone of the Karkonosze Mts. observed in the stand margins is over 26% and it is by 10% higher than the frequency of Ips typographus. An increased frequency of Ips amitinus was recorded in stems and rollers in the diameter size classes of 9–20 cm. When assessing the competitiveness for breeding sites between I. typographus and I. amitinus in areas of their joint occurrence, it may be stipulated that Ips typographus colonises first the assortments most preferred by that species, thus becoming the dominant species in those areas, while at the same time retreating in the other sections before Ips amitinus, which at a very strong population (as e.g. the one found in the analysed area) colonises them in such numbers that it limits the space for colonisation and development by Ips typographus.