Distribution of Range Plant Communities as Influenced by Edaphic Factors in Raudhat Khuraim

Raudhat Khuraim is a depression of extensive pans against a sand dune belt to the east of Irq Faydat Khuraim, located about 100 km north-east of Riyadh, Saudi Arabia. The Area collects water rain-flow from three watercourses draining eastwards. The area is liable for flooding. Therefore, soil water retention of the Raudhat is higher for a long time than the surrounding areas. High soil moisture is reflected on both vegetation distribution and soil properties. This study was aimed to define the distribution of range plant communities in the northern part of Raudhat Khuraim and to relate soil properties to vegetation cover and distribution. Fifteen plant communities, a semi-bare soil-and a bare soil were recognized. Perennial plant composition, total vegetation cover and species relative cover were defined. Soil samples by layers were collected for physical and chemical analyses. Texture, calcium carbonate, pH, cations, anions and organic matter were determined. Results revealed that soil properties had an influence on vegetation cover and the distribution of different plant communities with different degrees. Properties that had pronounced effect on the distribution of communities were texture, EC, cations of calcium, magnesium and sodium, chloride and bicarbonate anions and surface layer organic matter. Communities with very low vegetation cover had a soil with high magnesium cation in one or more of their profile layers