Effects of biological works within the integrated watershed management of torrent catchments in the area of Grdelica Gorge and Vranjska Valley (Serbia)

Integrated watershed management is based on the application of various biological and technical works, and administration measure to reduce the degradation process. The paper presents an analysis of the effects of performed biological works as part of integrated watershed management within the Grdelica Gorge and Vranjska Valley. Extensive erosion control works were carried out in the second half of the 20th century. As vegetation is one of the key factors in mitigating the erosion process, the paper presents the trend of connecting the surface with the vegetation cover, which results from implemented biological measures. Using multispectral satellite imagery (Landsat missions) for 1972, 1986, 1996, and 2017, the vegetation index (Normalized Difference Vegetation Index – NDVI) was analyzed in torrent basins, which were afforested to control severe erosion processes. The increasing trend of vegetated areas was recorded in period from 1986 to 1996 (very low vegetation coverage 40.19 % in 1986 and 8.19 % in 1996, respectively), which continues to grow until 2017 when the very low vegetation coverage was 0.26 %, and moderately high vegetation coverage was 50.63 %.