**3. Results**

#### *3.1. Summary of Model Validation*

The evaluation measures indicated that object-based random forest showed good performance in assessing the importance of variables that control the susceptibility of protected and non-protected forests to landslides. The optimal number of variables for every splitting in each tree was obtained as 7 and 11 in the protected and non-protected forests, respectively, depending on the minimum misclassification error (Figure 3a,b). The optimal AUROC values of protected and non-protected forest obtained about 86.31 and 81.77% after the formation of 500 trees. The sensitivity values of 77.54 and 74.56% were obtained from mapping the landslide susceptibility in the protected and non-protected forests, as shown in Table 3.


**Table 3.** The results of the accuracy assessment of landslide susceptibility mapping based on the influential variables that control the occurrence of the landslide in the protected and non-protected forests.

1 AUROC: Area under the receiver operating characteristics; 2 PF: Protected forest; 3 NPF: Non-protected forest.

#### *3.2. The Importance of Variables*

The analysis of variable importance indicated that the top variables that controlled landslide susceptibility belonged to the topographic and hydrologic categories in both the protected and non-protected forests. The most influential variables were terrain ruggedness index (TRI) and river density with 19.54 and 6.07% of importance values in the protected and non-protected forests, respectively (Figure 4). The triggering variables had a significant influence on the landslide susceptibility in both regions; however, the score values of natural triggering factors (16.20%) were higher than the values of anthropogenic triggering factors (<1%) in the protected forest. On the other hands, anthropogenic factors (16.89%) such as forest fragmentation, logging, and mining activities recorded slightly higher score values than the natural triggering factors (16.50%) such as rainfall, flood, and earthquake in the non-protected forest (Figure 4). The geological variables recorded higher values in the non-protected forest in comparison to the protected forest. The type of forest variable showed a score value of 2.58% in the protected forest and a trivial importance in the non-protected forest. However, soil variables recorded total values of less than one percent for expressing landslide susceptibility in the two study areas.

**Figure 4.** Comparison of the variable's importance in controlling the susceptibility of protected forest (**a**) and non-protected forest (**b**) to landslides in NE Iran. While topographic, hydrologic, and natural triggering factors were dominant variables in the protected forest, the anthropogenic triggering factors recorded higher importance values than the natural triggering factors with a total value close to the importance of topographic and hydrologic variables in the non-protected forest in NE Iran.

#### *3.3. Landslide Susceptibility Mapping*

The output maps indicate that the distribution of the landslide susceptibility of non-protected forest (0.51 ± 0.36) was higher than in the protected forest (0.34 ± 0.33) in the study area (Figure 5). The high susceptibility values of landslide were distributed in the east of the protected forest (Figure 5a), which resulted from the extremely rugged and steep surfaces as well as the magnitude of the occurred earthquake and hydrological variables such as topographic wetness index (TWI) and distance to river (Figure 4). Although di fferent parts of non-protected forest were occupied by high values of landslide susceptibility, those forests affected by the interaction of hydrologic and topographic variables with anthropogenic and natural triggering factors received higher values of landslide susceptibility, particularly in the central and southern parts of the non-protected forest (Figure 5b).

**Figure 5.** The landslide susceptibility maps of the protected forest (**a**) and the non-protected forest (**b**) in NE Iran. The maps show that the majority of high susceptibility values of landslide were distributed in the eastern parts of the protected forest (**a**) occupied by highly and extremely rugged or steep surfaces, while the high values of landslide susceptibility were distributed throughout the non-protected forest (**b**), particularly where anthropogenic and natural triggering factors interacted with the hydrologic and topographic variables.
