Hussein F. Farrag*
Little is known about the effects of soil variables on vegetation composition of many Wadis in Taif region. Wadi Al-Argy is one of the important wadis of Taif region (Saudi Arabia) sheltering a rich diversity of higher plants. In this study, three sites representing different habitats in Wadi Al-Argy were regularly visited during summer and winter growing seasons for one year; in each site 4 stands were selected for studying floristic composition and vegetation types in the area. Composition and diversity of vegetation were studied in relation to soil variables. A total of 75 species representing 27 families were recorded. The classification of vegetation using Two Way Indicator Species Analysis (TWINSPAN) resulted in the recognition of three vegetation groups representing Wadi bed, rocky slope and fallow land habitats. The application of Canonical Correspondence Analysis (CCA) indicated the recognition of three vegetation groups which aggregated along the ordination plane of the first and second axes. The TWINSPAN classification indicated considerable variation in the edaphic factors among stands of the different vegetation groups. The percentage of organic carbon attained maximum value of 2.61 % in the Wadi bed, while the minimum value of 0.88% was recorded in the fallow land. Electric conductivity greatly varied from a minimum (5.9 mmhos/cm) recorded in the Wadi bed habitat and this value was tripled (15.5 mmhos/cm) in the fallow land habitat.
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