The aim of this paper is to achieve a quantitative assessment of rockfall protection forest efficiency at regional scale, considering site specific forest, morphological and lithological parameters. At first, a semi-automatic GIS-based method, integrated with a multi-scenario 3D-rockfall model realized by using the simulation code HY-STONE, was used to map protection forests of Regione Lombardia (central Italian Alps). For each different forest type, a rockfall protective efficiency was assessed by using empirical (energy line angle) and modelling (HY-STONE) approaches. The empirical approach shows an increase of the energy line angle value from about 36° for the bare slopes to over 40° in forested slopes, with a value ranging from 37° to 44° for different forests types. The modelling approach is based on a new efficiency index EEI ranging from 0 (minimum efficiency, equal to no forest condition) to 1 (maximum efficiency): the efficiency of different forest types ranges from 0.08 to 0.98 by using average values of the controlling parameters. To modulate the efficiency in each single forest at regional scale, a set of parametric simulations was performed to evaluate the effects of controlling parameters. The parametric simulations show that block volume, slope gradient, DBH (diameter at breast height) and forest density are the most important parameters at controlling the efficiency. These parameters were used within a multiple linear regression function to associate a protection efficiency to each specific protection forest in the regional map. This allows to discriminate quantitatively the individual forests according to their actual efficiency. Most of the protection forest area (46%) shows an efficiency greater than 0.50 and only the 24% of the total covered area shows a value lower than 0.25.

中文翻译：

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区域尺度森林落石防护效率评估

本文的目的是在考虑特定地点的森林、形态和岩性参数的情况下，对区域尺度的落石防护林效率进行定量评估。首先，采用半自动基于GIS的方法，结合使用模拟代码HY-STONE实现的多场景3D落石模型，绘制了Regione Lombardia（意大利中部阿尔卑斯山）的保护林。对于每种不同的森林类型，通过使用经验（能量线角度）和建模（HY-STONE）方法评估落石保护效率。经验方法表明，能量线角度值从裸坡的约 36° 增加到森林覆盖的斜坡的 40° 以上，不同森林类型的值范围从 37° 到 44°。建模方法基于新的效率指数 EEI，范围从 0（最低效率，等于没有森林条件）到 1（最高效率）：通过使用控制参数的平均值，不同森林类型的效率范围为 0.08 到 0.98 . 为了在区域尺度上调节每个单一森林的效率，进行了一组参数模拟来评估控制参数的效果。参数模拟表明，块体积、坡度、DBH（胸高直径）和森林密度是控制效率的最重要参数。这些参数在多元线性回归函数中使用，以将保护效率与区域地图中的每个特定保护林相关联。这允许根据它们的实际效率定量地区分单个森林。大部分保护林面积（46%）的效率大于 0.50，只有总覆盖面积的 24% 的值小于 0.25。