干旱区生态环境知识资源中心

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 and 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 alla-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 and 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.