Silva Fennica : quarterly issues : 30(2–3) : sa3023169.htm

Tarmo Virtanen, Seppo Neuvonen, Ari Nikula, Martti Varama & Pekka Niemelä. 1996.

Climate change and the risks of Neodiprion sertifer outbreaks on Scots pine

Silva Fennica 30(2–3): 169–177

The European Pine Sawfly (Neodiprion sertifer) is one of the most serious defoliators of Scots pine in northern Europe. We studied the pattern in the regional occurrence of the outbreaks of N. sertifer in Finland in years 1961–90, and made predictions about the outbreak pattern to the year 2050 after predicted winter warming. We tested whether minimum winter temperatures and forest type and soil properties could explain the observed outbreak pattern. We analysed outbreak patterns at two different spatial levels: forest board- and municipal-level. The proportion of coniferous forests on damage susceptible soils (dry and infertile sites) explained a significant part of the variation in outbreak frequency at small spatial scale (municipalities) but not at large spatial scale (forest boards). At the forest board level the incidence of minimum temperatures below –36 °C (= the critical value for egg mortality) explains 33% of the variation in the outbreak pattern, and at the municipal level the incidence of cold winters was also the most significant explaining variable in northern Finland. Egg mortality due to cold winters seems to be the most parsimonious factor explaining why there have been so few N. sertifer outbreaks in northern and northeastern Finland. We predict that climate change (increased winter temperatures) may increase the frequency of outbreaks in eastern and northern Finland in the future.

Scots pine, Neodiprion sertifer, insect outbreaks, climate change, cold tolerance, GIS

Virtanen and Neuvonen, Department of Biology and Kevo Subarctic Research Station, University of Turku, FIN-20014 Turku, Finland; Nikula, Finnish Forest Research Institute, Rovaniemi Research Station, PO Box 16, FIN-96301 Rovaniemi, Finland; Varama, Finnish Forest Research Institute, Vantaa Research Centre, PO Box 18, FIN-01301 Vantaa, Finland; Niemelä, Faculty of Forestry, University of Joensuu, PO Box 111, FIN-80101 Joensuu, Finland. Fax (Virtanen) +358 2 333 6550, E-mail

Received 22 September 1995 Accepted 24 May 1996
ISSN 0037-5330