Species richness and diversity in the vegetation of the western mediterranean coastal desert of Egypt

Abstract

The Mediterranean desert west of Alexandria (Mariut) is one of the arid regions which has a long history of intensive land-use. The evaluation of the diversity of its plant resources and the effect of land-use on such diversity is the main objective of the present study. In the present study, species diversity was assessed by several indices. The simplest index is merely the number of species in a comrmmity (or habitat) and is called " species richness". Taxonomic diversity was calculated at both genus and family levels on the same Jines as species richness. Other diversity measures take into account two factors, species richness and evenness (sometimes known as equitability), that is how equally the species are. Species abundance models were also used to describe the distribution of species abundances in different commwrities. The highest species richness and diversity was recorded on ridges ( 1 02 perennial species and I 04 annual species) and non-saline depressions, (I13 perennial species and I I I annual species) which may be attributed to the remarkable land heterogeneity in these two habitats. The present study ;llso reveals that the high species richness and diversity in these two habitats is again exhibited in the species richness and diversity of their commwrities. On the other hand, the flora of salt marshes is very poor (21 perennial species and 9 annual species) since only few species are adapted to drought particularly where salinity is a limiting factor. It is also remarkable that taxonomic diversity of different habitats in the study area has an opposite trend to species richness: habitats of high species richness (non­ saline depressions, ridges and wadis) are oflow taxonomic diversity, and the habitats of low species richness (salt marshes and saline depressions) are of high taxonomic diversity. Dwing the process of coastal dune stabilizlltion plant species diversity generally increases and reaches a maximum in the stabilized dune community, coinciding with the decrease in dominance. Species distribution curves also show a clear progressive increase