Journal of Arid Environments (1988) 15, 283-296 The structure of the sand dune ecosystem of Wadi El Raiyan, Egypt Mostafa A. Saleh*, S. A. Saber and Mahmoud A. Saleh Accepted 4 February 1988 Physical and biotic elements of a sand dune ecosystem in the Wadi El Raiyan area of the Egyptian Western Desert are identified and described. The study area is the site of extensive eolian sand deposition and active dune formation. It has a typical hyperarid warm Saharan climate. A superfacial groundwater table is the main source of water. Vegetation is limited to low-lying interdune areas and the bases of larger dunes, and is represented by 13 species of perennial plants. Vegetation density, distribution and composition vary with local topographic and edaphic variations. Animal life is concentrated in the vegetated areas and is represented by a large number of invertebrates, mostly insects and arachnids. Eleven reptiles, 13 resident birds and nine mammals, are also present, many with adaptations for either sandy or other desert habitats. The special characteristics of this ecosystem and its elements are discussed. Introduction Landform patterns, provide a variety of microhabitats that differ in water resources, soil properties and microclimatic conditions in arid regions (Kassas & Batanouny, 1984), and thereby determine the nature and distribution of plant and animal life. For desert biota, the characteristics of these microhabitats are ecologically more important than the regional climatic conditions of the area as a whole (Mosauer, 1934; Grenot, 1974). In the Sahara, extensive dune systems are crucial sites for local ground water recharge by past and present precipitation and run-off water from surrounding, often higher areas (Davis, 1974; Grenot, 1974); these form superficial water tables beneath the dunes (Ranwell, 1972). The permanent, moist layer of sand often just below the surface of the lower slopes of large dunes, and in hollows between them (Migahid & Abdel Rahman, 1953; Bagnold, 1954a & b) renders sand dunes second only to wadis and oases as water resources (Grenot, 1974). The availability of soil moisture, coupled with the physical characteristics of deep sandy soil, provide a most favorable water regime for desert vegetation (Kovda et al., 1979). Geography, geology and geomorphology of sand dunes of the Western Desert of Egypt have been extensively investigated (cf. Bagnold, 1935; El Baz, 1984). Flora and plant ecology of sandy habitats of that desert have been studied in a number of oases (Migahid et al., 1960; Boulos, 1966; Zahran, 1966, 1972; Zahran & Girgis, 1972)and in the Mediter- ranean coastal dunes (Ayyad, 1973). Information on the ecology of animals of sandy habitats in that desert is scattered through a number of publications (Flower, 1933; Kamal et al., 1966a & b; Meinertzhagn, 1930; Moreau, 1966; Osborn & Helmy, 1980). The • Present address: Department of Biology, University of Bahrain, P.O. Box 32038, Bahrain, Arabian Gulf. Department of Zoology, Faculty of Science, Al Azhar University, Nasr City, Cairo and Department of Agricultural Biochemistry, Faculty of Agriculture,CairoUniversity, Giza, Egypt. 0140-1963/88/060283+ 14$03.00/0 © 1988 Academic PressLimited