Norway spruce (Picea abies (L.) H. Karst.) selection forests at Siljansfors in Central Sweden

Abstract

Continuous cover forestry (CCF) is a type of forest management which is based on ecological principles and avoids clearfelling as much as possible. A specialised form of CCF is the selection system which relies on inhomogeneous size structures in mixed-species forests and on the harvesting of individual dominant trees. The selection system was originally invented by upland farmers in Central Europe some 500 years ago and is fairly uncommon in Northern Europe. In our research, we studied two more or less mono-species Picea abies selection forests at Siljansfors in Central Sweden that have a comparatively low final stem diameter of 50 cm. We involved dynamic demographic equilibrium modelling to identify an ideal size structure as a reference that ensures sustainability. We compared this reference with the observed empirical stem-diameter distributions and found that both stands are indeed advancing towards the structure typical of single-tree selection systems. One stand is particularly close to this ideal, sustainable structure whilst the other requires more goal-orientated management in the future. Our research confirmed that selection forests with largely only one conifer species and a fairly small final diameter are possible at this latitude. We could also show that the dynamic demographic model can be converted to a simpler static model that is easier to apply in forest practice. Since selection stands are rare in Fennoscandia, the two stands studied at Siljansfors have been and will continue to be important research and management demonstration sites in the future.

Keywords

• Continuous cover forestry (CCF)
• Schütz model
• q factor
• Growth dominance
• Gini index
• Homogeneity index