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ŠUMARSKI LIST 9-10/2021 str. 54     <-- 54 -->        PDF

In the context of an integrated watershed management system, biological works are an essential component. The application of biological works (mainly different afforestation methods) creates a protective vegetation cover that protects the soil from the degradation process (Durán and Rodríguez, 2008). The positive effects of biological works are not evident immediately after construction because vegetation cover requires a more extended period to establish an assembly that could resist erosion processes (Kostadinov, 2008).
A traditional method used (e.g., field survey, literature study, analysis of already existing maps) for vegetation analysis is time-consuming and often too expensive (Pitt et al., 1997; Xie et al., 2008). More recently, the effects of afforestation (vegetation conditions) can be determined based on the analysis of satellite images and the corresponding vegetation indices (Campbell and Wynne, 2011). This method offers a faster and economical solution for analyzing the vegetation condition in the researched area. The remote sensing method enables the observation of vegetation in different scales from local (Xiao et al., 2017) to global (Nemani et al., 1996; Wu et al., 2014; Richards and Belcher, 2019), and such data are used in studies of vegetation change induced by climate change (An et al., 2018), anthropogenic or some other impact (Kumari et al., 2020). In this way, it is possible to determine potential areas for afforestation (Bhagat, 2009), monitor the carbon cycle in nature (Xiao et al., 2019), forest health (Barka et al. 2018), or the condition of crops on arable land (Zhang et al., 2014).
On the Republic of Serbia’s territory, the Grdelica Gorge and Vranje Valley area stands out, which was endangered by excessive erosion processes in the past due to specific natural and socio-economic conditions. An erosion map for this area created in 1953 was the base point for the implementation of anti-erosion biological work. The map was produced using the Erosion Potential Method, which is developed within this research area and it is commonly used and applicable worldwide (Serbia, Italy, Iran, Greece, China, USA) (Zorn and Komac 2008; Amini et al. 2010; Tošić et al. 2012; Ristić et al. 2013; Dragičević et al. 2018). The erosion coefficient values (Zsr) range from 0.1 to 1.5, i.e., from areas not affected to areas with excessive erosion (Gavrilović, 1972).
In the 1950s, torrential floods caused a noticeable destructive effect and side effects on the economy and the environment (Gavrilović 1972; Petković 1981; Braunović 2013; Kostadinov et al. 2018). To reduce the adverse effects of torrential floods and erosion processes in this area, for the first time in the Republic of Serbia, numerous biological and technical works and specific measures against erosion have been performed within the integrated watershed management. As part of the biological works, the afforestation of bare land was performed. The technical works included the construction of various facilities in the riverbed (dams and floodgates), while the administrative measures included multiple types of restrictions on activities that influenced the development of erosion processes (grazing ban, ban on cutting leaves). Biological works have enabled the establishment of vegetation cover able to protect the soil from erosion processes, while administrative measures have raised the awareness of local people of the importance of vegetation in soil erosion protection.
This research aims to analyze the effects of performed biological works in Grdelica Gorge and Vranjska Valley using remote sensing data. The Normalized Difference Vegetation Index (NDVI) was used to detect the change in vegetation from 1972, 1986, 1996 to 2017.
MATERIALS AND METHODS
MATERIJALI I METODE
Research area – Područje istraživanja
The area of Grdelica Gorge and Vranje Valley is situated in the southeastern part of the Republic of Serbia (Figure 1) cover 1784.34 km2 and represent two interconnected units located between 42° 22‘ and 42° 55’ north latitude and 19° 21‘ and 20° 00’ east longitude.