Ecological relations between plant distribution and edaphic factors in coastal plains were recorded in 45 stands (20 x 20 m each) distributed of Jazan region, Saudi Arabia. The main aim of this study was to examine the spatial pattern of vegetation and relationship between vegetation composition and environmental factors on Jazan area. The present study provides quantitative estimates of the vegetation structure and the distribution of the plant communities in coastal plains of Jazan region in relation to the soil properties. The environmental data included elevation, slope degree and exposure. Analysis data involved two steps: classification (using TWINSPAN) and ordination ( using CANOCO). The factors affecting the species distribution and correlation between the vegetation gradients and the edaphic variables are discussed. Ten major community types constitute the major part of the natural vegetation of the study area and are dominated by ten perennials: Acacia tortilis (Forssk.)Hayne., Suaeda monoica Forssk., Tamarix aphylla (L.) Karst., Cyperus conglomerates Rottb., Ziziphus spina-christi (L.)Willd., Panicum turgidum Forssk., Savadora persica L., Calotropis procera (willd) R. Br., Tephrosia apollinea (Del.) and Leptadenia pyrotechnica (Forssk)Decne. The complex interaction of different environmental factors in relation to edaphic variables leads to variation of habitat types and different plant distribution communities. Data analysis showed that pH, moisture, electrical conductivity, organic carbon, calcium carbonate, bicarbonate, soil cations: sodium, potassium, calcium, and the sodium adsorption ratio are the main operating edaphic factors in jazan area. The results of this study confirm that the study area is a subtropical desert and belongs floristically to the Sudanian territory and also that therophytes are the most frequent lif-form in this region.
Key words: Jazan region, edaphic factors, plant distribution, climat, correlation
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