Phytosociology and size structure of Nitraria retusa along the Egyptian Red Sea coast

摘要

The present study aims at analyzing the phytosociological behavior and size structure of Nitraria retusa (Forssk.) Asch shrub along the Egyptian Red Sea coast in relation to the prevailing environmental gradients. The application of TWINSPAN and DCA multivariate techniques led to identifying five vegetation groups associated with the distribution of this plant in this region. These groups are named after their characteristic species as follows: Typha domingensis, Zygophyllum coccineum-Zilla spinosa, Tamarix nilotica-Zilla spinosa, Nitraria retusa-Zygophyllum album and Nitraria retusa. The two groups of Nitraria retusa had, on average, the lowest species diversity and their stands had the highest soil salinity and clay contents. In general, the population of this plant is characterized by relative preponderance of the small-sized individuals (i.e. juveniles) particularly in the sites of medium positions along the prevailing salinity gradient. On the other hand, the juveniles are highly stressed in the stands of hypersalinity. The negative relationship between the density and size of this plant suggests that its size is density-dependent.