Vegetation associations in the Ougarta Mountains and dayas of the Guir hamada, Algerian Sahara

The description of the associations of two desert landform systems in Algeria, the rocky hills (djebels) of the Ougarta Mountains and the silty-sandy depressions (dayas) scattered on the Guir hamada, are presented. Numerical classification using two-way indicator species analysis and cluster analysis were applied to the data set to identify the vegetation units. These are subsequently described within the phytosociological framework recognized in this part of the Sahara. Two new sub-associations emerged for the djebels and are related to precise geomorphological units. These are a cliff sub-association defined by Withania adpressa and an open, flat ground sub-association characterized by Gymnocarpos decander. Numerical classifications allowed to get a first insight into the structure of the data. The Braun-Blanquet method was useful for further interpretation when comparing with data from similar habitats. Analysis of the floristic lists of previous workers with those of the present study highlighted the disappearance of several species of tropical origin in the djebels.