After excessive cutting in Swiss mountain forests and extirpation of most of the wildlife during the past centuries, efficient forestry and hunting laws allowed a wide regeneration of the forests and a rapid increase of ungulate populations in the present century. As a consequence, the impacts of ungulates on the vegetation became obvious. Regeneration of forest trees, however, is influenced not only by ungulates, but by a number of physical site factors and biotic impacts. As these impacts and their interactions vary extensively, regeneration is neither spatially nor temporally constant. Most of the presently used tree-regeneration methods, however, assume constant conditions, which renders a proper evaluation of tree regeneration in mountain forests and the role of ungulates impossible. Furthermore, the effect of this variation on forest development and forest functions is unknown with regard to the long term. While society requires a multipurpose mountain forest, structured at a small scale, wild ungulates use their habitat at a larger scale. This often leads to conflicts. Consequently, solutions including different scales are necessary. A lack of knowledge will, therefore, have to be met by research making data available to the practice as well as through coordinated investigations and experiments.