Regional assessment of land cover change in North Africa during the 20th century: combining recent global remote sensing products and historical maps

Abstract

The Mediterranean basin has been exploited for crops and pastures for centuries, and drastic economical changes have occurred during the 20th century, with world wars, colonization of the southern bound of the basin, and the European collapse of traditional agriculture in the Mediterranean region. Landscape cover changes on the northern side of the Mediterranean have been well documented. We propose here to fulfil the gap of knowledge on land cover at the regional scale covering the whole Northern Africa, based on the comparison of early and late 20th century data. Historical analysis relies on topographical maps, compared to remote sensing products. We use 4 different products (FRA, GLC, UMD, IGBP) crossed with tree-cover of UMD-GLCF for assessing accurate spatialized vegetation pattern. Assessment and validation are obtained by control points on local national forest inventories. We suggest a methodology for producing an accurate land cover map from global datasets; comparison and crossing of different datasets is essential for obtaining accurate land-cover classification of Mediterranean type ecosystems. Result analysis shows degradation of the southern Mediterranean vegetation over the region, with deforestation dynamic being higher than reforestation during the last 50 years. Positive dynamics occur near coastline where population density is high while the southern bound seems to suffer from dry conditions, which will have to be explored more precisely