Water as resource and disturbance for wadi vegetation in a hyperarid area (Wadi Sannur, Eastern Desert, Egypt)

The structure of vegetation in Wadi Sannur (31°28′E, 29°10′N; Egypt) was analysed on a district scale, along 4 km of a wadi course where flooding occurs approximate every 7 years. Two hundred observations by point-quadrat, located on 45 transects, were made. Four types of habitats were sampled: terraces, channels, banks and bars. Each sample included the list of perennial species with cover estimation and superficial texture of substrate with estimation of grain size cover. Granulometric analysis shows that the samples are organized by their constituent proportions in fines particles, coarse particles (e.g. gravels, pebbles, cobbles) and bare rock. Floristic analysis of perennial species separate five communities among a common set of species. The co-analysis of the floristic and the granulometric data sets shows the relationships between vegetation and superficial texture: Pulicaria crispa (Forrsk.) Oliv. in Grant. community and Zilla spinosa (Turra) Prantl. community are found in fine grain sizes, the former in channel and the latter on banks. Achillea fragantissima (Forrsk.) Sch. Bip. community and Ochradenus baccatus Delile community are located on coarse substrates, the former in channel and the latter on banks and Haloxylon salicornicum (Moq.) Bunge ex. Boiss. community on bare rock. The distribution of vegetation communities is discussed in relation to flood disturbance, water resources and species strategy.