THE PLANT BIODIVERSITY OF THE WADI-ALLAQI-BIOSPHERE-RESERVE (EGYPT) -IMPACT OF LAKE NASSER ON A DESERT WADI ECOSYSTEM

A data set comprising 95 stands of desert vegetation, collected from t he Wadi Allaqi Biosphere Reserve and its environs within the South-Eas tern Desert of Egypt during 1985-90, was analysed using multivariate p rocedures (two-way indicator species analysis: TWINSPAN; detrended cor respondence analysis: DCA; canonical correspondence analysis: CCA), to produce a classification of plant communities in the area, and to exa mine the relationships of these plant communities to natural and man-i nduced features of the physical environment of the area (in particular , the influence of Lake Nasser, a major impoundment of the River Nile formed in 1964). The vegetation classification produced groupings broa der, in both floristic and ecological terms, than those found by earli er studies of this area. In total 78 plant species were recorded from four phytogeographic elements. Four principal vegetation groups were i dentified, of which one is new to the area, and is the result of major environmental changes affecting the downstream part of the Wadi Allaq i system; following periodic flooding of the wadi by Lake Nasser durin g the past 30 years. This community was indicated by Tamarix nilotica. There was a strongly-zoned (downstream-upstream) pattern to the veget ation within this lower part of Wadi Allaqi, which appears to be a fun ction of the probability of flooding by the lake. The remaining three vegetation groups occur higher in the wadi basin, Groundwater-dependen ce appeared to be important in defining a group indicated by Acacia to rtilis; as well as the Tamarix nilotica group. The two remaining group s, characterized respectively by Acacia ehrenbergiana and Cullen plica tum, represent vegetation groups which are precipitation-dependent, an d which tolerate drier conditions within the Allaqi system.