Our study of the biodiversity of the vegetation and the stability of the soil surface at the levels of the dunes fixed by Retama retam Webb., Tamarix gallica L., Tamarix aphylla (L.) Karst and the natural fixation in the two experimental projects of the dunes fixation in Zahrez Gharbi of El-Mesrane region (W. Djelfa) shows that the dunes fixed by T. gallica and T. aphylla represent an important diversity with 57 species, 36 species in the dunes fixed by R. retam Webb. and T. aphylla (L.) Karst and a significant diversity of 24 species at the levels of the dunes naturally fixed. The Shannon weaver –index (H’) registered on the vegetation of the dunes fixed by T. gallica L. and T. aphylla (L.). Karst is of H ' = 3.12; it is 2.61 at the levels of dunes fixed by R. retam Webb. and T. aphylla (L.). Karst, It achieved a 2.18 on the vegetation of the natural regeneration of R. retam Webb and sandy plants. On the qualitative plan, the distribution of the biologic types is marked by the dominance of the therophytes of the flora. The multidimensional treatment demonstrated that the moisture, the fertility and the soil stability are the ecological factors responsible for the composition and the repartition of the vegetation in the several studied dunes which demonstrates that there is noticeable dunes stability through the mechanical and biological treatment realized on these dunes.
Key words: Zahrez Gharbi, desertification, El-Mesrane, fixation, dunes, cordon.