Environmental correlates of species distribution in arid desert ecosystems of eastern Egypt

This paper gives a quantitative account of a recent study of vegetation-environment relationships along four transects crossing the northern part of the inland arid desert of Egypt. The vegetation data set was based on cover values from 200 stands; environmental analysis included percentages of surface sediments of different size classes, soil pH, total soluble salts, soil moisture, organic carbon and calcium carbonate. TWINSPAN classification and complementary DCA analysis of the data set yielded 21 vegetation clusters, assigned to six vegetation types dominated by 27 indicator species: some are characteristic of specific habitats, and others indicate transitions between groups of habitats. Application of Detrended Canonical Correspondence Analysis (DCCA) indicated that silt, clay, moisture content, organic carbon and calcium carbonate were the main abiotic environmental variables correlated with species distribution in the study area. A total of 141 plant species belonging to 32 different families were recorded in this study, mostly of Saharo-Arabian distribution, with therophytes followed by chamaephytes dominating the life-form spectra. High species richness was recorded in vegetation of sand plains, moist muddy flats and runnels, contrasting with salinized and limestone plains. Soil texture, organic carbon and moisture content are correlated with species diversity in the richer habitats, while high salinity and calcium carbonate are the main factors associated with lower species diversity. (C) 1998 Academic Press Limited.