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 degrees 28'E, 29 degrees 10' N; Egypt) was analysed on a district scale, along 4 km of a wad course wher e flooding occurs approximate every 7 years. Two hundred observations by po int-quadrat, located on 45 transects, were made. Four types of habitats wer e sampled: terraces, channels, banks and bars. Each sample included the lis t of perennial species with cover estimation and superficial texture of sub strate with estimation of grain size cover. Granulometric analysis shows th at the samples are organized by their constituent proportions in fines part icles, coarse particles (e.g, gravels, pebbles, cobbles) and bare rock. Flo ristic analysis of perennial species separate five communities among a comm on set of species. The co-analysis of the floristic and the granulometric d ata sets shows the relationships between vegetation and superficial texture : Pulicaria crispa (Forrsk.) Oliv. in Grant. community and Zilla spinosa (T urra) Prantl. community are found in fine grain sizes, the former in channe l and the latter on banks. Achillea fragantissima (Forrsk.) Sch. Bip. commu nity and Ochradenus baccatus Delile community are located on coarse substra tes, the former in channel and the latter on banks and Haloxylon salicornic um (Moq.) Bunge ex. Boiss. community on bare rock. The distribution of vege tation communities is discussed in relation to flood disturbance, water res ources and species strategy. (C) 1999 Academic Press.