We used one of the few rockfall models explicitly taking trees into account and compared the results obtained with the 3D simulation model RockyFor with empirical data on tree impacts at three mountain forests in Switzerland. Even though we used model input data with different resolutions at the study sites, RockyFor accurately predicted the spatial distribution of trajectory frequencies at all sites. In contrast, RockyFor underestimated mean impact heights observed on trees at the two sites where high- and medium-resolution input data were available and overestimated them at the site where input data with the lowest resolution data were used. By comparing the results of the simulation scenarios ‘‘current forest cover’’ and ‘‘non-forested slope’’, we assessed the protective effect of the current stands at all three sites. The number of rocks reaching the bottom parts of the study sites would, on average, almost triple if the ‘‘current forest cover’’ were absent. We conclude that RockyFor is able to predict the spatial distribution of rockfall trajectories on forested slopes accurately, based on input data with a resolution of at least 5 m
5 m.With the increasing availability of high-resolution data, it provides a useful tool for assessing the protective effect of mountain forests against rockfall.