Zur Waldinventur gehört die Überwachung der Vitalität | Monitoring vitality is an important task for forest inventories

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We are interested in a continuous and healthy forest cover. Therefore vitality and stability of trees should be taken into account in most inventories. These factors influence the future development of the forest and are indispensable for economical as well as ecological planning. Forecasts on the basis of models that do not make use of this information are not always reliable. Increment is one of the best indicators of vitality. In addition,crown defoliation should be estimated, even though this estimator has a large random error and it is well known that only heavy crown defoliations cause an essential loss of productivity. On the other hand, it has also been known for some time that even small crown defoliation rates are correlated with subsequent mortality. Moreover, for Norway spruce and silver fir in the range 0–25% crown defoliation is strongly correlated with diameter increment, if trees are compared strictly within sample plots. Surprisingly, crown defoliation is also an indicator of diminished storm stability. No other quantitative estimator for crowns is as reliable and, despite the initial difficulties in its estimation,crown defoliation is an important indicator for vitality. Changes over time are even more valuable than the absolute value. It is alarming that the number of trees with crown defoliation of more than 25% tripled in Switzerland between 1985 and 2000 – a statistically highly significant increase. Storm damage analysis has shown that infections in butt and roots considerably increase future storm risk. A relatively simple examination of the supporting roots for infections now turns out to be an efficient method to assess tree stability. Further investigation shows strong correlations between infections in the supporting roots of Norway spruce and silver fir and increment and crown defoliation. Evidently, infections in the roots may show the cause of the correlations of crown defoliation and the rate of mortality, increment and storm stability. It is, of course, not possible to monitor vitality and stability in a comprehensive way. However, decisive information on the sustainability of the growing stock can be gained with clearly justifiable costs. These possibilities have not been fully exploited.