Floristic composition and vegetation: Environmental relationships of Wadi Fatimah,Mecca, Saudi Arabia

The present study aimed to determine floristic composition, the structure of the vegetation, and species distribution at 16 sample plots in Wadi Fatimah, Mecca, Saudi Arabia, highlighting the ecological factors that affect species distribution. The study revealed 100 plant species belonging to 34 families. Fabaceae and Poaceae were the dominant families, and chamaephytes and therophytes were predominant life forms, which demonstrate a typical desert life-form spectrum. Altitude showed a highly significant association with species frequency distribution. The highest species richness value of 23 species per plot was recorded in the coastal plain (Vegetation groups II & III). The lowest species richness value of 9 species per plot was recorded in the littoral salt marsh (Vegetation group I). Chorological analysis exhibited the Saharao-Arabian–Sudano-Zambezian chorotypes, 47% of the studied species were bi-regional. Using TWINSPAN, DCA, and CCA multivariate analysis, four major vegetation groups were classified into three main ecosystems (I) Halopeplis perfoliata, Suaeda fruticosa, Acacia tortilis, and Suaeda fruticosa, representing the littoral salt marsh; (II) Rhazya stricta and Haloxylon salicornicum, characterized by the coastal plain; and (III) Senna italica, Glinus lotoides, and Tribulus macropterus were the leading groups in the inland mountainous country. The CCA ordination showed that the separation of Vegetation group III along the axis was affected by Mg, K, and P concentration, and VG IV was significantly associated with silt, clay, and fine sand content. Furthermore, the Vegetation group I was significantly correlated with Na and Ca concentration, and VG II group was significantly correlated with heavy metal concentrations of elements as Fe, Pb, Zn, Ni, and Cu.