Effectiveness of structure improvement thinning on stand structure in subalpine Norway spruce ( Picea abies (L.) Karst.) stands

Abstract

In the Swiss mountains there are numerous Norway spruce stands which have never or have not received silvicultural treatment for a long time. It is feared that the stand structures and, therefore, stand stability, i.e. resistance against storms and snow loads, will decline to such a degree that their protective function against natural hazards will be reduced. In this study, such stands, which local forest services consider having unsatisfactory structures and being unstable and with little regeneration, were subjected to a first thinning operation. Selected silvicultural treatments to maintain and improve the mechanical stability of the stands with the long-term goal of transforming them into mountain selection forests are presented. The subsequent development of the stands will be monitored and analysed. The effects of the treatments on structure and stand stability will be examined in the long-term by comparisons to adjacent stands with similar structures and similar stability which have received no treatment. First results concerning the effectiveness of the applied silvicultural measures regarding stand structure are analysed. It seems that the variables h/ d ratio, spatial distribution and the stand density index (SDI) are the best indicators of the effectiveness of the silvicultural treatment.