Selecting tree species for use in rockfall-protection forests

Research on protection forests designed to alleviate rockfall hazard has increased enormously over the last decade. Data are available concerning the most suitable stem spacing and density regimes in stands. The species used in protection forests can also influence enormously the effectiveness of the forest in conferring a protective role. Little information exists, however, about either the mechanical resistance of different species to rock impacts or the recovery processes after sustaining a wound. This paper provides a short review of the work carried out on the mechanisms by which different subalpine forest species sustain rockfall impacts, and considers the management of protection forests in relation to species and time. Broadleaved species are generally more mechanically resistant than conifers and heal more quickly after wounding. When felled, trees can be used as barriers to obstruct or change the trajectory of falling rocks. If used as such, the decay rates of logs from coniferous species tend to be lower than those for typical subalpine broadleaved species. By accumulating and integrating existing knowledge, a forester must determine the exact nature of the hazard on a given site, and the role of the protection forest. Typical subalpine broadleaved species are more efficient in protecting human life and property against rockfall activity, but are less effective than conifers in preventing winter snow movement.