Worldwide, mountain forests represent a significant factor in reducing rockfall risk over long periods of time on large potential disposition areas. While the economic value of technical protection measures against rockfall can be clearly determined and their benefits indicated, there is no general consensus on the quantification of the protective effect of forests. Experience shows that wherever there is forest, the implementation of technical measures to reduce risk of rockfall might often be dispensable or cheaper, and large deforestations (e.g. after windthrows, forest fires, clear-cuts) often show an increased incidence of rockfall events. This study focussed on how the protective effect of a forest against rockfall can be quantified on an alpine transregional scale. We therefore estimated the runout length, in terms of the angle of reach, of 700 individual rockfall trajectories from 39 release areas from Austria, Germany, Italy and Slovenia. All recorded rockfall events passed through forests which were classified either as coppice forests or, according to the CORINE classification of land cover, as mixed, coniferous or broadleaved dominated high forest stands. For each individual rockfall trajectory, we measured the forest structural parameters stem number, basal area, top height, ratio of shrub to high forest and share of coniferous trees. To quantify the protective effect of forests on rockfall, a hazard reduction factor is introduced, defined as the ratio between an expected angle of reach without forest and the back-calculated forest-influenced angles of reach. The results show that forests significantly reduce the runout length of rockfall. The highest reduction was observed for mixed high forest stands, while the lowest hazard reduction was observed for high forest stands dominated either by coniferous or broadleaved tree species. This implies that as soon as one tree species dominates, the risk reduction factor becomes lower. Coppice forests showed the lowest variability in hazard reduction. Hazard reduction due to forests increases, on average, by 7% for an increase in the stem number by 100 stems per hectare. The proposed concept allows a global view of the effectiveness of protective forests against rockfall processes and thus enable to value forest ecosystem services for future transregional assessments on a European level. Based on our results, general cost–benefit considerations of nature-based solutions against rockfall, such as protective forests as well as first-order evaluations of rockfall hazard reduction effects of silvicultural measures within the different forest types, can be supported.

中文翻译：

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在区域尺度上评估高山森林对落石的保护作用

在世界范围内，山地森林是长期减少大型潜在处置区落石风险的重要因素。虽然可以明确确定防落石技术保护措施的经济价值并显示其效益，但对森林保护效果的量化尚未达成普遍共识。经验表明，只要有森林，实施降低落石风险的技术措施往往是可有可无的或成本更低，而大面积的森林砍伐（例如风抛、森林火灾、砍伐之后）往往会增加落石事件的发生率。这项研究的重点是如何在高山跨区域尺度上量化森林对落石的保护作用。因此，我们根据可达角估计了跳动长度，来自奥地利、德国、意大利和斯洛文尼亚的 39 个释放区的 700 条单独的落石轨迹。所有记录的落石事件都经过森林，这些森林被归类为矮林，或者根据 CORINE 土地覆盖分类，被归类为混合、针叶或阔叶为主的高林分。对于每个单独的落石轨迹，我们测量了森林结构参数的茎数、基面积、顶部高度、灌木与高林的比例以及针叶树的份额。为了量化森林对落石的保护作用，引入了减灾因子，定义为没有森林的预期到达角与反向计算的受森林影响的到达角之间的比率。结果表明，森林显着减少了落石的跳动长度。混合高林分的减少幅度最大，而以针叶树或阔叶树种为主的高林分则观察到的危害减少最低。这意味着一旦一种树种占主导地位，风险降低系数就会降低。矮林在减灾方面的变异性最低。每公顷茎干数量增​​加 100 根，森林带来的危害减少平均增加 7%。提议的概念允许对保护性森林抵御落石过程的有效性进行全球观察，从而能够评估森林生态系统服务的价值，以便在欧洲层面进行未来的跨区域评估。根据我们的结果，基于自然的解决方案的一般成本效益考虑，以防止落石，