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ŠUMARSKI LIST 7-8/2020 str. 71     <-- 71 -->        PDF

determined (Figure 5). In this system that looks out for tens of square kilometres of areas, areas that were not visible due to the topographic impact although they were inside the effective detection radius, areas that were outside the detection radius as they went beyond the optimum lookout distance and areas that were visible from one tower or several towers could be identified.
The network of towers in the study area could view 56% of the overall area and 59% of the forest areas (Table 4). These results revealed that 41% of the forests in the study area were invisible. It can be suggested that the rate of invisible forestland is high for an area with fire sensitive tree species and stands (Neyişçi, 1987). Moreover, as the Mediterranean climate characteristics lead to increased danger of forest fire, the forest fire risk is maximum in summer in this region (Neyişçi, 1987). As it was possible to assess the existing tower network in three-dimensional analyses in this study, the observation capacity through the existing tower network, which was constructed without digital data and methods and fire risk analysis, and its disadvantages, could be determined.
The horizontal distance between the neighbouring towers in the network in this region ranged from 5 km to 55 km. The average distance is lower between the towers inside the forests. In this way, several towers can view one place. Table 5 shows the spatial distribution of the areas that were visible from one tower or several towers according to the viewshed analysis, while their spatial distribution is shown in Figure 6. The presence of towers that are 5 km close to one another is an indication that the terrain where the forests in the area are distributed is very rugged. Despite that, 21% of the forests was invisible and 18% was outside the observable range of the towers.
The fire risk of the invisible forest areas in this region was assessed by overlapping the fire risk zones map developed by Bereket (2019) with the viewshed analysis map (Figure 7). The spatial distribution of areas invisible from lookout towers across the fire risk classes demonstrates that 15% of the invisible forest areas had relatively higher fire risk (Table 6). After nine towers neighbouring with the study area were included, only 1% of the previously invisible high fire-risk areas became visible.
In order to test the visibility of forests in the region from the vehicles moving on the highway, viewshed analysis was conducted on points designated at an interval of 100 m on this road axis (Figure 8). From those roads, 52% of the forest area was visible.