Plant communities in two vegetation transects in the extreme desert of western Egypt
Abd El-Ghani, Monier M.; Bornkamm, Reinhard; Darius, Frank
In the Western Desert of Egypt two vegetation transects at ca 30 °N (near the Siwa Oasis) and ca 26 °N (near the Dakhla Oasis) have been described by 144 vegetation relevés. In each relevé relative density of individuals, frequency and cover were recorded and in combination expressed as importance value. Soil samples were taken and analysed for eight soil parameters. By tabular comparison 12 vegetation units were discerned. Three of the units were already known as associations, another association was split into two, and seven units were described as communities. Six units occur predominantly in the Northern Transect, the six other ones predominantly in the Southern Transect. The comparison with the TWINSPAN-analyses by Abd El-Ghani (2000a) shows coincidence of the two classifications in many cases, but in some cases differences make clear where further research is needed. All units are dominated by the saharo-arabian geoelement; contributions of the mediterranean geoelement are higher in the Northern Transect, of the sudanian geoelement higher in Southern Transect. Since both transects are established over limestone bedrock on soils with sandy surface many soil characters are rather similar. The main differentiating factor is electrical conductivity. Four of the units grow in saline habitat, eight in non saline habitat. Also regarding pH value, contents of organic matter, CaCO3 and grain sizes (sand versus silt + clay) statistical differences were found and discussed. The Southern Transect shows higher sand contents (and consequently lower contents of silt + clay) than the Northern Transect. Syntaxonomy of the higher phytosociological units was discussed mainly on the basis of alliances with the result that more data are needed on order to come to a better understanding of the relations between the units adopted.