Epidemiological analysis of inventory data shows that rot in roots is closely correlated with needle loss and increment, the variables most commonly used to assess health and vitality of trees. An accurate observation of trees damaged by storms shows that for Norway spruce, rot in the supporting roots as well as rot in the butts is responsible for a large part of storm damage. The importance of rot in the roots has been considerably underestimated up to now. For inventory purposes the surveying method must be objective, non-destructive, and relatively fast. The method of checking butts for rot by extracting cores is known. A similar method is applied for the supporting roots. At least for spruce this is quite simple but has never been done before. In the Swiss Plateau rot in roots seems to be one of the main diseases and may explain the health deficit of spruce trees to some extent. By checking for butt and root rot, it is possible to get a better assessment of stability as well as of vitality of spruce forests. In the future it will often be advisable to include observations of rot in Butts and roots in forest inventories.
