Wind and snow damage in a thinning and fertilization experiment in Picea abies in southern Sweden

Summary Changes in susceptibilit y to wind and snow damage due to thinning and fertilization were examined in even aged Norway spruce (Picea abies (L.) Karst.) stands in southern Sweden. The stands are part of a nationwide experiment to investigate growth and yield following different thinning and fertilization regimes established between 1966 and 1983. The material used in this study included 16 replications of seven treatments. The treatments were: three levels of thinning from below (20-70 per cent); 20 per cent thinning from above; thinning from below in combination with N and NP fertilization (thinning percentage 25—28 per cent); and unthinned control. The stands have been censused twice for damage during an average period of 12 years. The degree of wind and snow induced damage varied between 9 and 20 per cent of the basal area increment produced during the observation period. For treatments with high basal area removal, the highest relative number of trees damaged by wind occured during the first period after thinning. The densest stands (i.e. unthinned controls and stands thinned from above) showed a high proportion of snow damage throughout the observation period. The block effect was in general more significant than the effect of treatments on damage level. When analysing the influence of the block effect (i.e. of site and stand characteristics) on damage level, wind damage was best predicted by stand basal area left after thinning and stand age, while snow damage was best predicted by latitude, altitude, site index, and stand age. On average the tested site and stand characteristics explained 17 per cent of the variation in wind damage and 36 per cent in snow damage.

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