30 years of protection and monitoring of a steppic rangeland undergoing desertification.
Résumé
Stipa tenacissima L., which has long been recognised as the typical dominant perennial plant in the North-African arid rangelands is currently going into extinction in the steppic High Plains of Algeria. The vegetation and soil dynamics were analyzed at an initially dense stand. The trend between 1976 and 2006 was investigated using five reference years. Sampling was performed along a grazing gradient including a grazed steppe and an exclosure. Between 1976 and 1993, the perennial cover and soil organic matter decreased outside the exclosure, while the composition of the dominant species remained unchanged. From 1993 to 2006, the plant cover, species composition and soil showed major changes both inside and outside the exclosure and S. tenacissima disappeared completely in 2006. These changes were primarily attributed to overgrazing by sheep. More frequent and intensive droughts exacerbated the grazing intensity in a context of common and uncontrolled land use. The exclosure, implemented as a remedy, temporarily played a positive role regarding vegetation and soil conservation. In addition to severe drought, the vegetation and soil degradation and sand encroachment even inside the exclosure, created conditions that were no longer able to support the pre-existing alfa-grass ecosystem.