Numerical modelling of natural hazards has become a valuable tool for scientists and engineers. However, most of the actual modelling techniques cannot be applied to specific problems in the forest zone. They treat situations in open areas and mostly do not consider the particular conditions of the vegetation cover in general and forest effects in special. These remarks must be considered for both the starting zone and the transition and runout zones individually. This contribution is aimed only to specific forest aspects of avalanches, rockfalls, landslides, debris flows and extreme water runoff. The more general aspects of models and research needs will be treated in other papers of this conference (Ammann, 1999); overviews for Swiss conditions and research institutions may be found in BUWAL (1998), and Vision (1998).