Coppice forest stands can play a key protective role on active rockfall slopes in mountainous regions. This paper aims at quantifying their protection function and at explaining the role of different stand parameters in this function. To achieve these objectives we first made field inventories focussing on the dendrometric and spatial characteristics of 13 coppice stands. Then, we developed a 2D simulation model, called RockCop, to quantify their protective function against rockfall. The simulations show that the predominant size of the falling rocks conditions which of the dendrometric stand parameters mainly determine the protective function of a coppice stand. In the case of small rocks (20 cmØ), we conclude that a higher stand density improves the protective function. Thus, for those rocks, young stands are most adequate. An acceptable level of protection against medium sized rocks (50 cmØ) is only fulfilled by few coppice stands and determined by specific combinations of stand density, stem diameters, basal area and species composition. None of the investigated stands offer sufficient protection against large rocks (1 mØ).