prilagođeno pretraživanje po punom tekstu

ŠUMARSKI LIST 9-10/2021 str. 55     <-- 55 -->        PDF

This area belongs to the upper basin of the South Morava. The average altitude is 790 m a.s.l. (above sea level), and the average angle of inclination is 14.8 °C. The Mediterranean and continental climate influence the average annual air temperature to be 10.9 °C, and the total annual rainfall to be 672 mm (RHMZ 2011). Grdelica Gorge consists of 137 torrents of different hydrographic classes, and the Vranje Valley 73 torrents streams. The investigated area’s geological basis consists of crystalline shales, micashists, gneisses, chloritoshists, quartz shales, phyllite, etc. (Kostadinov et al., 2018).
Grdelica Gorge and Vranjska Valley are characterized by a mosaic structure of the soil types. Some of them are most widespread, like Dystric Cambisol, Eutric Cambisol, Haplic Cambisol, Haplic Vertisol, Ranker, Regosol, and Fluvisol (Lukić 2013; Kostadinov et al., 2018). Most of the biological works were performed on the Dystric and Eutric Cambisol (Lukić 2013).
Developed landforms and a rich hydrographic network through climatic factors affect the weathering of poorly resistant geological substrates, making this area sensitive to erosion processes. According to the potential vegetation map (1986), characteristic vegetation communities of this area are Turkey oak and Hungarian oak (Quercetum frainetto-cerris) and Montane beech forest (Fagetum moesiacae montanum). In the valley of South Morava River, the forests of pedunculate oak and broom (Genisto elatae-Quercetum roboris) and forests of poplar and willow (Salici-Populetum albae) are dominating (Lukić 2013).
Within the anti-erosion biological works (afforestation) which was performed in the 1950s, some other species were introduced (black and white pine (Pinus nigra and Pinus strobus), black locust (Robinia pseudoacacia), Turkish hazel (Corylus colurna), common walnut (Junlas regia)) (Braunović 2013).
Methodology – Metodologija
Remote sensing data were used to analyze the effects of biological measures of erosion control afforestation. Normalized Difference Vegetation Index (NDVI) reflects the state of vegetation cover as the essential component of soil erosion protection. NDVI is one of the most used vegetation indices (Jiang et al., 2006), which is determined using the near-infrared (NIR) and visible red (Red) spectra of radiation.
The data for the NDVI calculation were taken from the satellite images for 1972, 1986, 1996, and 2017. Vegetation index varies from -1 to 1 (Table 1). Constructed areas, road networks, barren, and water areas, and the NDVI index value are below zero. Investigated area vegetation coverage is performed based on the table classification (Table 1).
Multispectral satellite imagery was downloaded from the server and belongs to various Landsat missions. A multispectral satellite image from the Landsat 1 mission was used for the earliest observation series. As Landsat 1 mission products are available at the L1TP processing level, a georeferencing method had to be applied (Campbell and Wynne, 2011). Atmospheric correction was performed on all satellite images (Landsat 1, 7, 8). As the first intensive biological works were performed in the 1950s, finding a suitable satellite image from the earliest year with the least atmospheric and visual anomalies was necessary. The first available satellite images of the study area are from 1972, and the best images for October in that year. Since the recording in 1972 is essential as a zero point, the other recordings were taken for October for an accurate comparison. Processing of the satellite images, calculations of the vegetation index (NDVI), and spatial analysis were performed using ArcMap 10.8.1 (ESRI, Redlands, CA).
This research detected a significant change in vegetation cover in the studied period 1972 – 2017. The NDVI index values on intensive or excessive erosion areas for the observed years are shown in Figure 2. Also, Figure 4 shows the percentage of areas according to different classes of NDVI index. According to the results, there is a significant difference in the NDVI index in 2017 compared to the zero condition (1972).
The extent of the categories of excessive and intensive erosion was shown on the erosion map from 1953 (Figure 3), which was also the basis for the implementation of planned biological works to prevent erosion processes. A large part of erosion control afforestation in the investigated area was carried out in the late 1950s and early 1960s (Braunović 2013). Beneficial effects of biological works were evident