Ecological Modelling 221 (2010) 290–302 Contents lists available at ScienceDirect Ecological Modelling journal homepage: www.elsevier.com/locate/ecolmodel Sanitary felling of Norway spruce due to spruce bark beetles in Slovenia: A model and projections for various climate change scenarios Nikica Ogris a,∗ , Maja Jurc b a Slovenian Forestry Institute, Veˇ cna pot 2, SI-1000 Ljubljana, Slovenia b University of Ljubljana, Biotechnical Faculty, Department of Forestry and Renewable Forest Resources, Veˇ cna pot 83, SI-1000 Ljubljana, Slovenia article info Article history: Available online 24 June 2009 Keywords: Picea abies Ips typographus Pityogenes chalcographus Model tree Ecology Forest management abstract A model is presented to predict sanitary felling of Norway spruce (Picea abies) due to spruce bark beetles (Ips typographus, Pityogenes chalcographus) in Slovenia according to different climate change scenarios. The model incorporates 21 variables that are directly or indirectly related to the dependent variable, and that can be arranged into five groups: climate, forest, landscape, topography, and soil. The soil properties are represented by 8 variables, 4 variables define the topography, 4 describe the climate, 4 define the landscape, and one additional variable provides the quantity of Norway spruce present in the model cell. The model was developed using the M5 ′ model tree. The basic spatial unit of the model is 1 km 2 , and the time resolution is 1 year. The model evaluation was performed by three different measures: (1) the correlation coefficient (51.9%), (2) the Theil’s inequality coefficient (0.49) and (3) the modelling efficiency (0.32). Validation of the model was carried out by 10-fold cross-validation. The model tree consists of 28 linear models, and model was calculated for three different climate change scenarios extending over a period until 2100, in 10-year intervals. The model is valid for the entire area of Slovenia; however, climate change projections were made only for the Maribor region (596 km 2 ). The model assumes that relation- ships among the incorporated factors will remain unchanged under climate change, and the influence of humans was not taken into account. The structure of the model reveals the great importance of landscape variables, which proved to be positively correlated with the dependent variable. Variables that describe the water regime in the model cell were also highly correlated with the dependent variable, with evap- otranspiration and parent material being of particular importance. The results of the model support the hypothesis that bark beetles do greater damage to Norway spruce artificially planted out of its native range in Slovenia, i.e., lowlands and soils rich in N, P, and K. The model calculation for climate change scenarios in the Maribor region shows an increase in sanitary felling of Norway spruce due to spruce bark beetles, for all scenarios. The model provides a path towards better understanding of the complex ecological interactions involved in bark beetle outbreaks. Potential application of the results in forest management and planning is discussed. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Some species of spruce bark beetles (e.g., Ips typographus L. and Pityogenes chalcographus L.) can break out under favourable ecolog- ical and trophic conditions. The outbreaks of spruce bark beetles can have devastating consequences on forests. This has been con- firmed by data regarding the sanitary felling of conifers in Slovenia during the period from 1995 to 2006. In 2005, for example, around 747,000 m 3 of wood were felled due to bark beetles, which is 22.9% of the total felled wood, or 9.9% of the total yield in Slovenia (ZGS, 2006). Such episodes allow us to define spruce bark beetles accord- ing to the classification of disturbance described by Anko (1993), ∗ Corresponding author. Tel.: +386 1 2007833; fax: +386 1 2573589. E-mail address: nikica.ogris@gozdis.si (N. Ogris). as a complex, natural, and chronic disturbance (sometimes even as an acute disturbance). A natural disturbance of the forest ecosys- tem means a swing between succession and dynamic equilibrium (Anko, 1993). In light of climate change, spruce bark beetles can be treated as a disturbance that affects the dynamics of the for- est ecosystem, and also as a factor that is affected by such climate changes (Berryman, 1986; Malström and Raffa, 2000). Studies have shown that the behaviour of spruce bark bee- tles will likely change due to climate change. For example, researchers are expecting a drastic increase in damages caused by Ips typographus in Scandinavia over the next decade, because higher temperatures will allow this species to produce two com- plete generations per year instead of the single generation they currently produce (Lange et al., 2006). In Slovenia, I. typographus reproduction is developing towards two complete and one sister generation per year (Jurc, 2008). In Scandinavia, the border for sur- 0304-3800/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.ecolmodel.2009.05.015