EFFECT OF ENVIRONMENTAL-FACTORS ON THE FLORA OF ALLUVIAL FANS IN SOUTHERN SINAI

The purpose of this study was to elucidate the floristic and structura l characteristics of simple alluvial fan vegetation of southern Sinai and to relate them to environmental variation. The main question addre ssed was: how does the floristic composition of fan habitats, species richness and life-form vary in relation to environmental change! Thirt y-seven alluvial fans, randomly selected in two main wadis (Wadi Feira n and Wadi Dahab) were analysed quantitively. Two-way Indicator Specie s Analysis (TWINSPAN) classification and Canonical Correspondence Anal ysis (CCA) were applied in successive stages of the data analysis to d escribe vegetational variation in relation to physical gradients. Seve n main clusters of fans were defined on the basis of environmental var iation. These clusters are divided into three main groups of species r ichness. Species richness varied along a moisture gradient. The riches t fans were the driest habitats, indicating that maximum species richn ess did not occur at high moisture availability. The moisture gradient is a complex gradient correlated with elevation, slope, climatic arid ity, soil texture and the nature of the soil surface. Fine sand, silt plus clay and calcium carbonate showed significant differences between the internal groups and subgroups of the first and second level of th e TWINSPAN classification. (C)1996 Academic Press Limited