Forests are multi-functional ecosystems, but a major function is not well taken into account: the protective function against rockfall risks. Its why research institutes (dealing with mountain forest management and risk assessment) and private companies (working in the field of risk prevention) from France, Austria, Spain and Switzerland have decided to initiate a research project on this topic: the ROCKFOR project (http://rockfor.grenoble.cemagref.fr/). The duration of this project is 3 years and the starting date was the first of January 2001. The project aim is to incorporate tree mechanical behaviour in a spatial rockfall model in order to assess the efficiency of forest stands against rockfall and to produce management guidelines for sustainable rockfall hazard mitigation by mountain forests. This article presents the framework used for the tree mechanical behaviour modelling and the rockfall real size experiments methodology. As the data coming from these experiments will be used to realize a rockfalls simulation models benchmarking, we are not yet authorized to publish the data gained during these experiments.