Inventory and analysis of tree injuries in a rockfall-damaged forest stand

Rockfall is a major threat to settlements and transportation routes in many places. Consequently, the protective function of mountain forests has recently gained particular interest. However, much is still unknown about the ideal properties of protective forest stands. Therefore the present paper discusses a method for the inventory and analysis of tree injuries in a rockfall-damaged forest stand. With this method, the interrelation between stand geometry and rockfall injuries in a subalpine Polygalo chamaebuxi-Piceetum was examined. The study site of 0.3 Ha is located in the transit zone of frequently passing, small rockfall fragments (~10 cm in diameter) causing healable tree injuries. Tree and injury parameters were recorded and analysed as to injury number, height and size. The spatial distribution of the 157 trees (diameter at breast height dbh>5 cm) in the stand as well as of the 1,704 identified rockfall injuries showed a very uneven pattern. As expected, number, height and size of the injuries generally declined with increasing distance from the cliff as well as due to higher stem densities. In contrast, results indicated that the dbh of trees has no significant influence on the number of injuries per tree. However, this study showed a clear interrelation between tree and injury distribution: in general, large trees close to the cliff and smaller trees with a high density further down the slope seem to be favourable for good protection. At least an uneven-aged, multilayered stand should be sustained. Overall, the combined analysis of stand geometry and injury parameters provides information on the spatial distribution of rockfall and on the influence of tree arrangements.