Floristic patterns and ecological drivers of sand dune ecosystem along the Mediterranean coast of Egypt

Most of the sand dunes close to the Mediterranean coast of Egypt have been destroyed due to human pressures. The remaining dunes are under extreme threat due to unplanned development. This study aims to explore the floristic patterns and detect which drivers threaten their conservation status. Eighty-five random plots of 100 m² each along 12 transects perpendicular to the seashore in the northwestern coastal dunes were sampled. Classification of plots using plant cover percentage was carried out through agglomerative hierarchical clustering and principal coordinate analysis. Canonical correspondence analysis (CCA) and variance partitioning (VP) were used to define the drivers that influence the floristic patterns. Therophytes and chamaephytes represent 30% of each of the 113 vascular plant species recorded in the present study. Four clusters of plant species corresponding to four dune-types were identified: Ammophila arenaria - Ononis vaginalis in foredunes, Echinops spinosissimus- Launaea fragilis in embryonic dunes, Echinops spinosissimus- Allium erdelii in transitional and Echinops spinosissimus- Thymelaea hirsuta in stabilized dunes. Stabilized dunes showed the highest diversity (species richness H_dune = 1.37, evenness E_dune = 0.88) and rarity indices (R = 0.52) as well as a steeper rarefaction curve. CCA disclosed that organic matter and CaCO₃ content, distance from the coastline, overcutting, trampling, and urbanization were correlated with the floristic patterns. VP showed that the examined variables justified for 53% of the variance in the floristic composition. Our results can be considered by managers to fulfill an appropriate conservation plan to preserve and manage the coastal dunes in arid regions.