Forests below rocky cliffs often play a very important role in protecting settlements against rockfall. The structure and development of these forests are expected to be substantially affected by the disturbance of the falling rocks. Knowing about this effect is important to predict the development of protection forests and consider potential effects of the falling blocks in management strategies. The goal of this study is to quantify differences in forest structure depending on rockfall activity in four different sites in the Swiss Alps. For this, we collected data on forest structure in zones of different rockfall activity and derived rockfall impact probabilities based on rockfall simulations. We assessed whether differences in forest structure and signs of rockfall disturbance could be observed between the rockfall zones. We additionally built mixed-effects models to identify the key variables explaining the forest characteristics described by diameter (DBH) and basal area (bA). The forest structure differs between the rockfall zones, however, with varying effects amongst the sites. DBH tends to decrease with increasing rockfall activity, whereas tree density appears to be little impacted by rockfall. For most sites, the number of deposited blocks and the simulated tree impact probability have a significant effect in the models along with the species, whereas for one site, hardly any effect of rockfall was found. Our results, obtained either from direct measurements or modelling, show that rockfall can locally influence the structure of forests, whereas the influence depends on the frequency and intensity of the rockfall disturbance. Impact probabilities obtained by simulations can serve as a good proxy for rockfall disturbances.

中文翻译：

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瑞士阿尔卑斯山落石对森林结构影响的定量评估

岩石峭壁下的森林通常在保护定居点免受落石影响方面发挥着非常重要的作用。预计这些森林的结构和发展将受到落石扰动的重大影响。了解这种影响对于预测防护林的发展和考虑管理策略中落块的潜在影响很重要。本研究的目标是根据瑞士阿尔卑斯山四个不同地点的落石活动来量化森林结构的差异。为此，我们收集了不同落石活动区域的森林结构数据，并根据落石模拟得出了落石影响概率。我们评估了在落石区之间是否可以观察到森林结构和落石干扰迹象的差异。我们还建立了混合效应模型，以确定解释由直径 (DBH) 和基面积 (bA) 描述的森林特征的关键变量。然而，落石带之间的森林结构不同，在不同地点之间产生不同的影响。DBH 往往随着落石活动的增加而减少，而树木密度似乎受落石影响很小。对于大多数站点，沉积块的数量和模拟的树木撞击概率与物种一起在模型中具有显着影响，而对于一个站点，几乎没有发现任何落石影响。我们从直接测量或建模中获得的结果表明，落石可以局部影响森林结构，而影响取决于落石扰动的频率和强度。