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

In the Swiss mountains there are numerous Norway spruce stands which have n ever or have not received silvicultural treatment for a long time. It is fe ared that the stand structures and, therefore, stand stability, i.e. resist ance against storms and snow loads, will decline to such a degree that thei r protective function against natural hazards will be reduced. In this study, such stands, which local forest services consider having uns atisfactory structures and being unstable and with little regeneration, wer e subjected to a first thinning operation. Selected silvicultural treatment s to maintain and improve the mechanical stability of the stands with the l ong-term goal of transforming them into mountain selection forests are pres ented. The subsequent development of the stands will be monitored and analy sed. The effects of the treatments on structure and stand stability will be examined in the long-term by comparisons to adjacent stands with similar s tructures and similar stability which have received no treatment. First res ults concerning the effectiveness of the applied silvicultural measures reg arding stand structure are analysed. It seems that the variables hid ratio, spatial distribution and the stand density index (SDI) are the best indica tors of the effectiveness of the silvicultural treatment. (C) 2001 Elsevier Science B.V. All rights reserved.