Science et changements planétaires / Sécheresse


Biological and phytogeographical biodiversity of Stipa tenacissima L. formations in Algeria Volume 14, issue 3, JUILLET-AOÛT-SEPTEMBRE 2003


See all figures

Laboratoire d‘écologie végétale, Faculté des sciences biologiques, Université des sciences et technologie Houari Boumediène, BP 32, El Alia Bab Ezzouar, 16311 Alger, Algérie

Stipa tenacissima is a plant of great ecological (against the desertification) and economic (chiefly in the paper industry) importance. It occupied wide areas between the Tellian Atlas and the Saharian Atlas. Behind the apparent homogeneity of the alfa grass ecosystem there actually lies a great diversity when going into details. The analysis of the floristic catalogue of its various groupings and of its biological and phytoecological types helps to observe the impact of the anthropic action and of the climatic pejoration on biodiversity. This study shows that, biologically speaking, the retrogression of these formations causes a chamaephytisation, such that prickly species which have not economic interest are abandoned by the cattle ( Astragalus, Atractylis, Carduncellus...) and invade the degraded alfa steppes, and a therophytisation, whereby species that produce many seeds rapidly colonize free spaces. These species do have a pastoral interest, but they contribute very little to the vegetation cover, appear only at propicious periods and their cycle is very brief. From the phytogeographical point of view, this analysis points out to a definite reduction of the vegetation cover and to the notable presence of saharo‐arabics in groupings belonging to the matorrals. This northbound rise of xerics species is due to the denudation of the ground surface. The fact that rain water inflitration is deficient generates a pedoclimate which is not favourable to certain species even though the general climate is favourable to them. If no preservation measure is taken, we shall first see matorral species being replaced by xerics species to ultimately witness desertisation.