Habitat heterogeneity and soil-vegetation relations in South of the Nile Delta, Egypt

Résumé En

Floristic composition and soil characters in representative habitats of the southern Nile Delta region in Qalyubia were analyzed in terms of habitat variations and species diversity. A total of 90 sites were surveyed and nineteen environmental factors were recognized in four main habitats : canal banks, cultivated lands, waste lands and sandy plains. Basic statistical treatments were established by using SPSS v. 10.0. The produced data were subjected to cluster analysis by using MVSP v. 3.1 ; indirect and direct ordination methods i. e. Detrended and Canonical Correspondence analyses, respectively by using CANOCO v. 4.5. A total of 164 species representing c. 7.7% of the Egyptian plant species were recorded and their life-form spectrum was identified. The majority of species were belonging to the families : Gramineae, Compositae, Leguminosae and Cruciferae. The floristic similarity between the recognized habitats showed a significant positive correlation between the canal banks and cultivated lands. Cynanchum acutum subsp. acutum, Cynodon dactylon, Phragmites australis and Pluchea dioscoridis were of high ecological amplitude. Three main vegetation groups (i. e. weeds, halo/ helophytes and xerophytes) were recorded, and their controlling ecological factors were identified. Ordination analysis reveled that, the three groups were well segregated along the DCA axis 1, and were highly related to calcium carbonates, fertility and species diversity gradients in addition to the gradient of human interference. Canonical Correspondence Analysis (CCA) produced a similar pattern to that of the floristic Detrended Correspondence Analysis (DCA) and revealed that, the weed plants (i. e. vegetation group A) were highly associated with organic matter, phosphorus, potassium, saturation percentage, potassium cations and pH ; the Halo/ Helophytic plants (group B) with bicarbonates, sulphates, calcium, magnesium and sodium ; the xerophetic plants (group C) with CaCO 3 and pH.