This study aims to monitor the arid Algerian High Plateaus, a key region for pastoral activities which has suffered harsh and widespread degradation from the eighties. This area is not sufficiently known by the international scientific community. For this purpose, we considered phytoecological inventories and thematic maps that have been carried out during 30 years. Available data for the study are vegetation maps derived from aerial photographs (1975-1978) and from satellite imagery (2006). The parameters considered include vegetation, flora, and soil surface properties. The study area is part of the ROSELT/OSS (ROSELT: Réseau d'Observatoires de Surveillance Ecologique à Long Terme (Long Term Ecological Monitoring Observatories Network); OSS: Observatory of the Sahara and the Sahel) network observatory (OSS 2008). To assess land degradation, we used landscape ecology parameters. These include the number and surface area of vegetation units, synthesized by the large patch index and the Shannon landscape diversity index. All parameters reflect an increase in landscape heterogeneity. The largest decline is observed for Stipa tenacissima vegetation units constituting 2/3 of the landscape in 1978 and occupied just 1/10 in 2006. Vegetation units linked to degradation, such those dominated by Salsola vermiculata, inexistent in 1978, now dominate the steppe. Another result of the ongoing landscape degradation on the plateaus between 1975 and 2006 is the decrease of vegetation cover. In 1978, 1/3 of rangelands only had low vegetation covers, inferior to 15%. Presently 9/10 present the same class cover. This can be explained by severe spells of drought combined by an exponential rise of livestock during the last 30 years. This has in turn greatly undermined the fodder potential of the steppe. Results suggest that the "greening-up" described by several authors in the Sahel over the last 40 years is not observed in the Algerian, nor in the North African steppes. On the contrary, the desertification is still ongoing and the threshold of irreversibility seems to be imminent.
Assessment of desertification sensitivity in Algeria. The map of desertification sensitivity is established by MEDALUS approach developed for the Mediterranean region on the basis on desertification sensitivity index, itself developed from several relevant factors known to influence the degradation processes (climate, vegetation, soil, human activities). The preparation of each layer is obtained from the geometric mean of the weighted parameters chosen to characterize and quantify this factor. Cartographic and alphanumeric data are captured and structured in a database, managed and analysed by a Geographic Information System. The output data have enabled the development of maps with small scale describing quality indexes. The maps about quality as well as the map of desertification sensitivity were analysed.
Land degradation is one of the most important environmental threats facing the international community. In North Africa, many semiarid and arid regions are suffering significant land degradation, which can be an impediment to sustainable development. Therefore; land degradation is monitored in a regional context for a better understanding of its causes and consequences. One of the main consequences is a notable increase in sand encroachment with negative environmental implications. For this reason, the dynamics of sands between south-eastern Morocco and the wilaya of Nâama, south-western Algeria, was studied. Sand samples gathered from six distinctive areas were subjected to physicochemical, colorimetric (redness index), morphoscopic (circularity), and geochemical analysis, and studied statistically using an analysis of variance (ANOVA), wind direction data, ternary plots and a hierarchical cluster of trace elements (K, Rb, Fe, Ti, Ca and Sr). In all areas, a clear dominance of the sand fraction appeared showing percentages ranging from 89 to 96%. Sampled areas were all carbonated, and the pH was alkaline, with close values ranging from 8.4 to 9. The mean circularity values ranged from 0.67 in Merzouga (Morocco) to 0.80 in El Aguer (Algeria). The lowest value of the redness index was noted in Merzouga with a mean value of 4. The Algerian areas showed an almost similar redness index with a value of 6 but the highest value was noted in Saadana with a value of 11. Geochemical approaches, based on ternary plots and dendrogram cluster indicating the abundance of major elements (Fe, Ca and K), were used as indicators of wind transport. Results suggested the existence of a Regional Wind Action System (RWAS) implicated in the transport of sand from south-eastern Morocco and its redistribution towards south-western Algeria. Merzouga was connected to all areas but particularly to nearby Saadana and Kasdir in the Algerian territory.
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