In order to model explicitly in 3D rockfall on forested slopes, we developed a trajectory rockfall model based on the discrete element method (DEM). This model is able to take the complex mechanical processes involved during an impact into account (large deformations, complex contact conditions) and can explicitly simulate block/soil, block/tree contacts as well as contacts between neighbouring trees. In this paper, we describe the developed DEM model and we use it to assess the protective effect of different types of forests. In addition, we compared it with a more classical rockfall simulation model. The results highlight that the forests can significantly reduce rockfall hazard and that the spatial structure of coppice forests have to be taken into account in rockfall simulations in order to avoid an overestimation of the protective role of these forest structures against rockfall hazard. In addition, the protective role of the forests is mainly influenced by the basal area. Finally, the advantages and limitations of the DEM model were compared with classical rockfall modelling approaches.