Growth patterns as indicators of impending tree death in silver fir

Tree-ring-based growth patterns of dead and living European silver fir (Abies alba Mill.) trees from a forest stand in Slovenia were compared and used for mortality predictions through time by applying a logistic mortality model. The living trees were classified in 1988 as healthy (healthy crown, productive cambium) or declining (defoliated crown, nonproductive cambium). While the average growth curves of dead and declining trees decreased strongly for about 50 years, the growth rate of healthy trees showed only a weak decrease during the same period. Characteristic recent growth patterns of dead and declining trees were very low growth levels, negative growth trends, and a very low relative growth. Healthy trees, in contrast, showed significantly higher growth levels, positive growth trends, and higher relative growth. Based on growth trends and relative growth as independent variables, the derived logistic mortality model showed high accuracy in predicting dead and healthy trees. According to the model, the declining trees are at a very high risk of dying. Revisiting the living trees in 2003 showed that some of the declining trees had already died in the last few years. Periods of suppressed growth of dead, declining, and healthy trees were interpreted by the mortality model as being lethal only when the trees reached a certain size. The early detection of trees with increased mortality risk may help evaluate and control future mortality in forest stands affected by silver fir dieback.