Summary.-The Mediterranean desert of Egypt is distinguished here into «arid» and «hyperarid» provinces on the basis of the ratio between precipitation and potential evapotranspiration, and each is subdivided according to mean temperature of both the coldest and the hottest months. The arid provinces are :(a) the attenuated arid Mediterranean coastal belt, and (b) the accentuated arid inland province. The hyperarid provinces are :(a) with mild winter and very hot summer, (b) with mild winter and hot summer, and (c) with cool winter and hot summer. Spatial and temporal variations in elima tic elements in these provinces are provided.Local vegetational variations in each province are related to the impact of geomorphology and physiography on the local climatic and edaphic characteristics ; and the plant communities associated with these variations are listed.Résumé.-Le désert méditerranéen de l'Egypte est divisé ici entre deux catégories : provinces arides et provinces hyperarides, selon la relation qui existe entre les précipitations et l'éva-potranspiration potentielle ; chaque catégorie est subdivisée en fonction de la température moyenne des mois les plus froids et des mois les plus chauds. Les provinces arides sont :a) la ceinture côtière caractérisée par un climat méditerranéen aride atténué ; b) la province intérieure, avec un climat mé-diterranéen aride accentué. Les provinces hyperarides sont celles qui ont :a) un hiver modéré et un été très chaud ; b) un hiver modéré et un été chaud ; et c) un hiver froid et un été chaud. Les variations des éléments climatiques à travers le temps et l'espace dans ces provinces sont illustrées.Les variations dans le tapis végétal local de chaque province sont reliées à l'impact de la géomorphologie et de la physiographie sur les caractéristiques du climat local et du sol. Les communautés végétales liées à ces variations sont mentionnées.
The application of indicator species analysis has proved useful in classifying stands into groupings coinciding with topographic variations. 41 indicator pseudo-species are identified in the vegetation along a phytosociological gradient: some are characteristic of specific habitats, and the others indicate transition between groups of habitats.The use of qualitative estimations (transformed density records) in multivariate analysis in the present study indicates that they may be more preferable than quantitative estimations, because of their easy and fast recording in the field, and the less comprehensive computations, while yielding precise results.The X-axis of the reciprocal averaging ordination is related to the salinity and fertility gradients, while the Y-axis reflects soil texture.The phytosociological gradients of the canonical variate axes reflect essentially contrasts between groups of species, each correlated with one or the other of the environmental gradients.Comparing the results obtained by the two ordination methods (reciprocal averaging and canonical variates) we find that the first method detects the overall phytosociological changes along strong environmental gradients which would be helpful in studying large surveys. On the other hand, the second technique, which is mainly predictive, is more sensitive to changes within both the phytosociological and environmental gradients and can detect the impact of these changes on the overall variance of each gradient.
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