In 1990 and 1999 two heavy storms struck Europe, the worst gales ever recorded in Switzerland. Millions of cubic metres of standing spruce trees were subsequently attacked by the eight-toothed spruce bark beetle (Ips typographus L.). In Swiss forests, such heavy mass attacks have never been observed before. From 1990 to 1996 standing trees infested by beetles totalled 50% of the spruce timber thrown by the 1990 storm.
Logistics sometimes made it impossible to remove all windthrown timber before new generations of beetles emerged. Forest services and forest owners were forced to set priorities. The strained financial situation of many owners and ecological aspects were also reasons for changing forest protection strategies and leaving some storm and bark beetle damaged areas uncleared. In regions with such areas, the amount of subsequent bark beetle attack approximately doubled compared with other regions where storm damages and infestation spots were thoroughly cleared. To answer questions of new risk assessment, projects were started on scolytid behaviour in differently treated regions and in buffer zones.