Late Glacial and Holocene records of tree-killing conifer bark beetles in Europe and North America: Implications for forest disturbance dynamics

Abstract

Outbreaks of conifer bark beetles in Europe and North America have increased in scale and severity in recent decades. In this study, we identify existing fossil records containing bark beetle remains from the end of the Last Glacial Maximum (~14,000 cal. yr BP) to present day using the online databases Neotoma and BugsCEP and literature searches, and compare these data with modern distribution data of selected tree-killing species. Modern-day observational data from the Global Biodiversity Information Facility (GBIF) database was used to map recorded distributions from AD 1750 to present day. A total of 53 fossil sites containing bark beetle remains, from both geological and archeological sites, were found during our searches. Fossil sites were fewer in Europe (n = 21) than North America (n = 32). In Europe, 29% of the samples in which remains were found were younger than 1000 cal. yr BP, while in North America, remains were mainly identified from late Glacial (~14,000–11,500 cal. yr BP) sites. In total, the fossil records contained only 8 of 20 species we consider important tree-killing bark beetles in Europe and North America based on their impacts during the last 100 years. In Europe, Ips sexdentatus was absent from the fossil record. In North America, Dendroctonus adjunctus, Dendroctonus frontalis, Dendroctonus jeffreyi, Dendroctonus pseudotsugae, Dryocoetes confusus, Ips calligraphus, Ips confusus, Ips grandicollis, Ips lecontei, Ips paraconfusus, and Scolytus ventralis were absent. Overall, preserved remains of tree-killing bark beetles are rare in the fossil record. However, by retrieving bulk material from new and existing sites and combining data from identified bark beetle remains with pollen, charcoal, tree rings, and geochemistry, the occurrence and dominance of bark beetles, their outbreaks, and other disturbance events can be reconstructed.