DIGITALNA ARHIVA ŠUMARSKOG LISTA
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the change was even more noticeable, where moderately low and moderately high classes occupy the most significant part of the research area. Also, Figure 4 shows that in 2017 there is no classes of bare land, as well as very low vegetation coverage. According to Kostadinov et al. (2018), areas under forests increased by 21.77 % from 1953 to 2016, and areas occupied by meadows and pastures by 17.64 %. Restored forest vegetation in Grdelica Gorge and Vranjska Valley proved to be one of the most effective types of soil erosion protection because it reduces or eliminates runoff that leads to erosion (Lukić and Dožić 2012; Lukić et al., 2015; Perović 2015; Perović et al., 2018). The trend of increasing the area under vegetation, and at the same time decreasing the erosion process. During the time (from the 1980s till the present), the intensity of erosion decreases (Kostadinov et al., 2018). In 2010, less than 1 % of the surface was in the classes of excessive and intensive erosion (Table 2). Studies done in small catchment areas on a Loess Plateau in China show that soil erosion is inversely proportional to vegetation cover presents (Zhou et al., 2006; Zheng 2006; Zhao et al., 2013a; Zhao et al., 2013b; Zhao et al., 2018). The same studies also have found that 40 % of vegetation cover reduces soil erosion by 62 %, and 54 % of vegetation cover reduces erosion processes by 80 % (Wang et al., 2015). The trend of reducing bare land areas, i.e., increasing the area under vegetation cover in Grdelica Gorge and Vranje Valley, is observed from the 1980s until today (Kostadinov et al., 2018). This research confirms that biological works can significantly influence the improvement of the vegetation cover condition as one of the leading carriers of anti-erosion protection. Besides, the research results show that remote sensing methods can be effectively applied to analyze the effects of performed biological works. CONCLUSION ZAKLJUČAK In Grdelica Gorge and Vranjska Valley, the research results indicate the success of the integrated watershed management works and measures through reduction of the erosion intensity. The state of vegetation cover for 1972, 1986, 1996, and 2017 was determined based on the remote sensing data. The assessment of the state of vegetation for the mentioned periods was determined using the NDVI index. Based on the vegetation cover analysis from 1972, about 20 % of the investigated area was occupied by bare soil, while the majority part belongs to the class of very low and low vegetation coverage. The success of biological works can be noticed as early as 1986 when bare soils occupy minimal values, and the area with low vegetation coverage has significantly increased. The growth trend of vegetation coverage continues in 1996. Also, in 2017, the most noticeable change was compared to previous years, where the largest percentage of the area is moderately high and moderately |