Abstract
Ohud mountain is one of the main important historic sites in the Arab Peninsula, and it is distinguishable over the rest of the mountains in the region. No extensive floristic survey has been carried out on Ohud mountain because of the rugged topography of this mountain. The current study investigates the floristic diversity and the correspondence of environmental factors of the phytogeographical distribution of plants, based on the floristic analysis of the present region. The research question is about the relationships between the species diversity and the human impacts of populated area at lowlands around Ohud mountain. A total of 59 species belonging to 56 genera and 28 families were recorded. Asteraceae had the highest contribution, about 12% of the total plant species. The analysis of the life forms demonstrated the prevalence of therophytes (68%) followed by chamaephytes (24%), indicating the adaptation of these life forms to hyperarid conditions. The chorological analysis indicated the predominance of the bi-regional taxa over the other phytochoria. Most of the recorded plant species belong to Saharo-Arabian and Sudano-Zambezian (24%) phytochoria. TWINSPAN analysis was performed to detect the indicator species of different vegetation groups and confirmed by detrended correspondence analysis (DCA or DECORANA). It is concluded that species richness and diversity revealed clear variation along the mountain and among the studied sites. Plant species diversity and richness were more pronounced in the intermediate portion of the elevation gradients across the mountain, with a decrease in the high altitudinal belts. The decrease was also recorded at the lower altitudes, where human impacts clearly affected vegetation; leading to a decrease in alpha diversity. In addition, the beta diversity among moderately highlands and lowlands was considerably high indicating the heterogeneous species composition among the studied sites along mountain elevations. The general pattern of vegetation groups distribution is controlled by a number of environmental factors; such as latitude, longitude, elevation, organic matter and some anions and cations. A Canonical Correspondence Analysis (CCA) ordination revealed that the vegetation structure has a strong association with the latitude of the mountain followed by organic matter and Magnesium. It is recommended that the populated area should be subjected to restoration of mountain ecosystem that might be degraded by human activities.