DIACHRONIC STUDY OF PLANT COVER CHANGES IN A MOUNTAINOUS ECOSYSTEM BY SPATIAL REMOTE SENSING: CASE OF THE TESSALA MOUNTAINS (WESTERN ALGERIA)

A better understanding of the changing patterns of land use and land cover, is a major concern for countries where ecosystems are being severely degraded. Indeed, the dynamic feature of land use has important implications on natural resources. Our study conducted on the Tessala mountains, by using Normalized Difference Vegetation Index (NDVI), put in evidence the importance of changes in vegetation cover between 1987 and 2007. A pronounced regressive evolution is observed in south-east and north-west of the Tessala mountains, especially in the forest of Tessala, in the communes of Ain-Thrid, Tessala and Sehala. The main factors of environmental degradation, are : deforestation (over 26 offenses cut every year), overgrazing (420 crimes of illegal grazing every year), forest fires (more than 20 fires every year) and resultant erosion (more than 72 % of the area is concerned and mainly in the south-east).