ORIGINAL PAPER Inter-species interactions and ecosystem effects of non-indigenous invasive and native tree-killing bark beetles Bjørn Økland • Nadir Erbilgin • Olav Skarpaas • Erik Christiansen • Bo La ˚ngstro ¨m Received: 23 November 2009 / Accepted: 10 November 2010 Ó Springer Science+Business Media B.V. 2011 Abstract Frequent bark beetle outbreaks cause biome-scale impacts in boreal and temperate forests worldwide. Despite frequent interceptions at ports of entry, the most aggressive bark beetle species of Ips and Dendroctonus in North America and Eurasia have failed to establish outside their original home continents. Our experiments showed that Ips typog- raphus can breed in six North American spruce species: Engelmann spruce, white spruce¸ Sitka spruce, Lutz spruce, black spruce and red spruce. This suggests that differences between the Eurasian historical host and North American spruce species are not an insurmountable barrier to establishment of this tree-killing species in North America. However, slightly diminished quality of offspring beetles emerged from the North American spruces could reduce the chance of establishment through an Allee effect. The probabilistic nature of invasion dynamics suggests that successful establishments can occur when the import practice allows frequent arrivals of non-indigenous bark beetles (increased propagule load). Model simulations of hypothetical interactions of Dendroctonus rufipennis and I. typographus indi- cated that inter-species facilitations could result in more frequent and severe outbreaks than those caused by I. typographus alone. The potential effects of such new dynamics on coniferous ecosystems may be dramatic and extensive, including major shifts in forest structure and species composition, increased carbon emissions and stream flow, direct and indirect impacts on wildlife and invertebrate communities, and loss of biodiversity. Keywords Species introduction  Invasive species  Ips  Dendroctonus  Coniferous forests  Outbreak frequency Introduction Biological invasions represent a threat to the world native plant biota, including the coniferous forests that cover at least 31% of global forested areas. In northern forest ecosystems, coniferous forests constitute a large B. Økland (&)  E. Christiansen Norwegian Forest and Landscape Institute, P.O.Box 115, 1430 A ˚ s, Norway e-mail: bjorn.okland@skogoglandskap.no N. Erbilgin Department of Renewable Resources, University of Alberta, 230A Earth Sciences Building, Edmonton, AB T6G 2E3, Canada O. Skarpaas Norwegian Institute for Nature Research, Gaustadalle ´en 21, 0349 Oslo, Norway B. La ˚ngstro ¨m Department of Ecology, Swedish University of Agricultural Sciences, Box 7044, 750 07 Uppsala, Sweden 123 Biol Invasions DOI 10.1007/s10530-011-9957-2