Climatic change

Climate change may have profound effects on insects that cause widespread tree mortality and have significant impacts on European forest ecosystems.


The Eurasian spruce bark beetle (Ips typographus) is by far the most aggressive and serious insect pest in European spruce forests. The exact factors triggering outbreaks of the spruce bark beetle are not fully understood, but climatic variables significantly influence population levels. It is our goal to increase our understanding of how climatic factors influence the risk of bark beetle outbreaks through modeling and spatio-temporal analyses of data. Results from model simulations indicate that more often storms may lead to more frequent but shorter outbreak periods (Økland & Bjornstad 2006). A general temperature increase may, for example, lead to a northward expansion of the areas experiencing two beetle generations per year (Lange etal. 2006, 2009). However, the degree-sum at which a voltinistic change is adaptive will vary with other ecological factors as well, such as density dependence and seasonal variation in mortality and resource availability. Furthermore, it is not fully clear how the magnitude of forest damage will vary with voltinistic change.


Other insect species may become increasingly important pests in the future due to their range expansions and interactions with native pest species (Økland et al. 2009, 2011). Less significant pests that are already present may change behavior and become more eruptive due to changing conditions for pests and their tree hosts under a future climate (Økland 2014).


International publications

Kalinkat, G., Ammunét, T, Barton, M., Battisti, A., Eigenbrode, S.D., Jepsen, J.U., Lehmann, P., Neuvonen, S., Niemelä, P., Økland, B., Terblanche, J.S., Björkman, C. 2018. RE: Inadequate assumptions undermine efforts to forecast climate change-induced crop losses to pests. eLetter Science 361(6405), 16 Nov. LINK


Galko, J., Økland, B., Kimoto, T. et al. 2018. Testing temperature effects on woodboring beetles associated with oak dieback. Biologia DOI: LINK


Marini, L., Økland, B., Jönsson, A.M., Bentz, B., Carroll, A., Forster, B., Grégoire, J.-C., Hurling, R., Nageleisen, L.M., Netherer, S., Ravn, H.P., Weed, A. and Schroeder, M. 2017. Climate drivers of bark beetle outbreak dynamics in Norway spruce forests. Ecography 40: 001–010.


Økland, B., Nikolov, C., Krokene, P., Vakula, J. 2016. Transition from windfall- to patch-driven outbreak dynamics of the spruce bark beetle Ips typographus. Forest Ecology and Management 363: 63–73. LINK


Økland, B., Netherer, S., Marini, L. 2015. The Eurasian spruce bark beetle – role of climate. The Eurasian spruce bark beetle: The role of climate. Pages 202-219 in Björkman, C. & Niemelä, P. (eds.): Climate Change and Insect Pests. CABI Climate Change Series 7, Wallingford UK. LINK


Mayer, F., Piel, F.B., Cassel-Lundhagen, A., Kirichenko, N., Grumiau, L., Økland, B., Bertheau, C., Gregoire, J.-C., Mardulyn, P., 2015. Comparative multilocus phylogeography of two Palaearctic spruce bark beetles: influence of contrasting ecological strategies on genetic variation. Molecular ecology 24, 1292-1310. PDF


Kausrud, K., Økland, B., Skarpaas, O., Grégoire, J.-C., Erbilgin, N., Stenseth, N.C. 2012. Population dynamics in changing environments: the case of an eruptive forest pest species. Biological Reviews 87: 34-51. PDF

Jönsson, A.M., Harding, S., Krokene, P., Lange, H., Lindelöw, Å., Økland, B., Ravn, H.P., Schroeder, L.M. 2011. Modelling the potential impact of global warming on Ips typographus voltinism and reproductive diapause. Climatic Change 109: 695–718. PDF

Kausrud, K., Grégoire, J.-C., Skarpaas, O., Erbilgin, N., Gilbert, M., Økland, B., Stenseth, N.C. 2011. Trees Wanted – Dead or Alive! Host Selection and Population Dynamics in Tree-Killing Bark Beetles. Plos One 6:13. PDF


Økland, B., Erbilgin, N., Skarpaas, O., Christiansen, E. & Långström, B. 2011. Inter-species interactions and ecosystem effects of non-indigenous invasive and native tree-killing bark beetles. Biological Invasions 13(5): 1151-1164. PDF


Krokene, P., Lange, H. & Økland, B. 2010. Effects of climate change on the interaction between a bark beetle and its conifer host. In: Forests for the future: sustaining society and the environment. XXIII IUFRO World Congress, 23-28 August 2010, Seoul, Republic of Korea. The International Forestry Review 12: 388.

Lange, H., Økland, B., Krokene, P. 2009. To be or twice to be? The life cycle development of the spruce bark beetle under climate change. In: Minai, A.A., Braha, D. & Bar-Yam (eds.): Unifying themes in complex systems, pp. 251-258. Proceedings of the 6th International Conference on Complex Systems. Springer Verlag. ISBN 978-3-540-85080-9. PDF

Økland, B. Skarpaas, O. & Kausrud, K. 2009. Threshold facilitations of interacting species. Population Ecology 51: 513-523. PDF


Økland B, & Bjørnstad, O.N. 2006. A resource depletion model of forest insect outbreaks. Ecology 87(2): 283-290. PDF

Lange, H., Økland, B. & Krokene, P. 2006. Thresholds in the life cycle of the spruce bark beetle under climate change. Interjournal for Complex Systems 1648. PDF

Benestad, R. 2005. Storm frequencies over Fennoscandia - relevance for bark beetle outbreak. RegClim results. report 20/2005. PDF

Økland, B. & Berryman, A. 2004. Resource dynamic plays a key role in regional fluctuations of the spruce bark beetles Ips typographus. Agricultural and Forest Entomology 6: 141-146. PDF

Økland, B. & Bjørnstad, O.N. 2003. Synchrony and geographical variation of the spruce bark beetle (Ips typographus) during a non-epidemic period. Population Ecology 45: 213-219. PDF

Reports and popular scientific publications


Økland, B. 2014. Snøbrekk som billemat. Skog 2-2012: 18-19. PDF

Økland, B. 2014. Furuspinner - en glupsk nålespiser (front page of 3. October 2014). [Pine-tree Lappet - a ferocious needle eater] LINK


Økland, B. & Wollebæk, G. 2013. Granbarkbillen. Registrering av bestandsstørrelsene i 2013. Oppdragsrapport fra Skog og landskap 06/13: 14 s. [The Eurasian spruce bark beetle. Population records in 2013]. Yearly reports from the national monitoring program of the Eurasian sprucebark beetle in Norway can be downloaded here [in Norwegian]


Økland B., Krokene P., Lange H. 2012. Effects of climate change on the spruce bark beetle. ScienceNordic, January 27, 2012. PDF

Krokene, P., Økland, B. 2012. Barkebille blues. Chronicle in Dagens Næringsliv, 21 January 2012


Krokene, P., Økland, B. 2012. Stormfelt skog er billemat. Norsk Skogbruk 2-2012: 18-19.


Krokene, P., Økland, B. 2012. Barkbiller og stormfelt skog. Skog 1/12. PDF


Økland, B. 2009. Furuspinner: En glupsk nålespiser. Klimavinnere. Norsk Skogbruk 3-2009: 31. [in Norwegian] PDF

Krokene, P. & Økland, B. 2009. Klimavinnerne. Granbarkbillen - fra vondt til verre? Norsk Skogbruk 55(5): 32. PDF

Økland, B. 2009. Sultne målere søker mot nord. Norsk Skogbruk 55(7/8): 31. PDF

Økland, B. 2009. Klimavinnerne. Furubukken - den dødelige budbringeren. Norsk Skogbruk 55(9B/10): 32 PDF

Krokene, P. & Økland, B. 2009. Klimavinnerne. Kongleinsekter - nye trusler for skogens arvesølv? Norsk Skogbruk 55(11): 32. PDF

Økland, B. & Nilssen, A.C. 2009. Klimavinnerne. Sommerfugl med byks mot nord. Norsk Skogbruk 55(12): 21. PDF

Krokene, P., Lange, H. & Økland, B. 2009. Barkbiller – en joker i skogens CO2-regnskap? Norsk Skogbruk 3-2009: 32-33. [in Norwegian] PDF

Krokene, P., Lange, H. & Økland, B. 2007. Granbarkbillen – fra en til to generasjoner? Skogeieren 6-2007: 20-22. [in Norwegian] PDF

Økland, B., Krokene, P., Lange, H. 2007. Granbarkbillen – hyppigere og kortere utbrudd. Skogeieren 4-2007: 26-27. [in Norwegian] PDF

Økland, B., Krokene, P., Lange, H. 2007. Klimaeffekter på granbarkbillen. Klima 1-2007: 32-35. [in Norwegian] PDF