The dayas are depressions commonly found in arid areas, where rainwater and soil nutrients accumulate. This study aims to study the influence of sand encroachment on plant diversity in sandy dayas of Ghardaïa (Northern Algerian Sahara). Three representative dayas were selected through subjective sampling. In each daya, phytoecological surveys were conducted to study the influence of sand encroachment on the diversity of plant communities using diversity indices, functional traits, phytogeography, and species ecology. The results revealed the presence of 24 species divided into 23 genera and 18 families. The Asphodelaceae family was the most important (540 individuals), followed by Fabaceae (294 individuals) and Plantaginaceae (160 individuals). The spectrum of development strategies showed a dominance of perennial species in all dayas, regardless of the degree of sand encroachment, with proportions exceeding 80%. The spectrum of life forms revealed high proportions of chamaephytes in dayas 1 and 3 (80.02% and 98.1% respectively) and a high proportion of phanerophytes in daya 2 (73.79%). The dispersal spectrum showed a dominance of barochore species (96.68%) in daya 3 and zoochore species (88.76%) in daya 2. The analysis of the phytogeographic spectrum indicated the dominance of the Saharo- Arabian element in dayas 1 and 3 (59.73% and 99%) and the Mediterranean element in daya 2 (73.79%). The ecological spectrum analysis revealed that sand encroachment influenced phytodiversity in all dayas, with psammophytes representing more than 52% of the recorded species. Overall, this study provides essential data for the management of vulnerable dryland ecosystems.