Desertification in the Maghreb: A Case Study of an Algerian High-Plain Steppe

Abstract

Natural and semi-natural ecosystems of the Maghreb have been subject, for several centuries, to grazing and cultivation as dominant land-uses. Living in a Mediterranean climate which is generally arid, plant, animal and human populations developed diverse adaptive strategies to cope with such rough conditions. Forests and rangelands have been undermined by erratic droughts that seem to be becoming more frequent. During the last two or three decades, vegetation and soil resources, in particular those of arid lands, have been marked by a rapid and severe degradation. The major changes observed were the regression of perennial plants (ligneous and grasses) and sand encroachment that are recognised to be relevant indicators of desertification in North Africa and the Middle East rangelands. A brief overall view of the Maghreb is given and illustrated by an example from the steppe rangelands dominated by alfa-grass (Stipa tenacissima L.) as a case study. The basic results of long term monitoring of what was originally a typical and dense steppe of the arid High Plains of Algeria have shown that alfa steppes have nearly disappeared from pediment surfaces since the 1980s. Causes are multiple but overgrazing remains in the present case, the main and direct origin of degradation because of diverse social and economic reasons, human population and need increases and increases in sheep grazing pressure. Irreversible changes were assessed using a grazing gradient approach. The gradient was represented by a transect starting from a long-term ungrazed exclosure, representing the pre-existing system and ending at free grazed rangelands. The monitored alfa stand showed, at the beginning of the study, a high homogeneity of vegetation and soil features. Vegetation pattern was a mosaic with individual tussocks and interstitial bare soil. The long term monitoring showed significant changes of the dominant species phytomass, plant composition and diversity and soil characteristics. The results, showing a regressive trend of the principal attributes of the vital ecosystem, could be generalized to all steppe habitats that had been originally dominated by alfa-grass. The aim of this work is to improve knowledge about extent, causes and mechanisms of desertification in order to direct restoration and rehabilitation actions.

30 Years of protection and monitoring of a steppic rangeland undergoing desertification

“…The significant decreases in fine particles (silt, and clays) and organic matter, and the increase in soil sand in the grazed land, were the major changes in the soil properties in 1993 (Aidoud et al, 1999;Slimani and Aidoud, 2004). A decrease in, or even total disappearance of, perennial plants exposes the soil to erosion, particularly by wind, and alters its composition (Schuman et al, 1999).…”

“…Thus, one can assume that at first, the erosion of fine particles from the soil, is caused locally by livestock trampling in the grazed area. In addition to overgrazing, the extension of the sand deposition seems to have contributed to the decline of the alfa and the disappearance of its dependent species (Slimani and Aidoud, 2004).…”

“…Alfa is still described as the most representative dominant species in the arid High Plains of Algeria. However, due to desertification, the alfa steppe has virtually disappeared, and it only persists on mountain piedmonts bordering the high plains (Slimani and Aidoud, 2004;Aidoud et al, 2006).…”

“…A 12 ha exclosure was fenced in July, 1975 within an open rangeland grazed by sheep all the year-round. Eighteen years later, vegetation and soil analyses clearly showed that the original vegetation and soil conditions were maintained inside the exclosure, in contrast to the highly degraded land outside which had been subjected to uncontrolled grazing (Aidoud and Touffet, 1996;Aidoud et al, 1999;Slimani and Aidoud, 2004).…”

Plant community structure and diversity under grazing gradient in arid Mediterranean steppe of Algeria

“…As well as anthropogenic factors playing a leading role in the organization of vegetation structures [3]. Grazing is the dominant land use in Northern Africa [4]. According to Aidoud and Touffet, 1996 [5], overgrazing is the principal factor of the degradation of plant communities in North Africa.…”