SPATIOTEMPORAL EVOLUTION OF PLANT DIVERSITY AND EDAPHIC CHARACTERISTICS IN THE STEPPES OF ALFA (Stipa tenacissima) OF THE REGION OF SAIDA (WESTERN ALGERIA)

Our work is to follow the spatial and temporal variations of the floristic and soil parameters during three years of monitoring (2013- 2014 -2015), held in three sampling stations in the steppes of Alfa (Stipa tenacissima) in the municipality of Maâmora (region of Saida, western Algeria). For this, 21 phytosociological statements were conducted annually on the three sampling stations. Station 1 an exclosure where alfa is well developed, Station2 where alfa is moderately degraded and station 3 where alfa is degraded. The floristic survey has shown variability in the number of species annually following the annual rainfall variability. Indeed, a maximum rate of 29 species were found on the three stations in 2013 is the year when rainfall was significant (517 mm) and that, contrary to 2014 when drought was pronounced (295, 9 mm), resulting in a fall in the number of species to 22 species. Overall, the biological spectrum of these species is marked by the predominance of therophyts which are mainly dominated by Poaceae, Asteraceae and the Caryophylaceae during the observation period. The soil analysis shows that the soil of the three stations is silty-sandy texture, shallow poor in organic matter, low humidity, salt-free, alkaline pH with a rate appreciably total limestone. Changes in these edaphic parameters are very visible to the spatial and temporal scale considered in this work. The process of data obtained by the factorial analysis of correspondences (AFC) emphasize in the existence of two groups of stations. Group 1 is correlated to Station 1 (recovery rate of Stipa tenacissima (TR) = - 0,493), hemicryptophyts (He) = -0,424, geophyts (Geo) = -0,114, a soil surface horizon with improved thickness (PR) = -0,316, better moisture (HUM) = -0,102, organic metter (MO) = -0,278). Group 2 is correlated to stations 2 and 3 (therophyts (TH) = -0,103, chamaephyts (CHA) = 0,516, sand (SB) = 0,106. clays (AR) = 0,092, total limestone (CaT) = 0,197) reflecting the degree of middle of opening that is related to a gradient of aridity evolving on a substrate represented mainly by sand and silt, reflecting the degree of middle of opening that is related to a gradient of aridity.