The coastal roadside vegetation and environmental gradients in the arid lands of Egypt

A recent floristic and environmental survey was undertaken on the roadside verges along the main highway between El Arish and Rafah (31° 10'N, 33° 48'E and 31° 17'N, 34° 15'E) that extend for about 45 km on the northeastern Mediterranean coast of Sinai (Egypt). 63 stands were studied at 700-m intervals to represent the variation of vegetation, and to compile the floristic composition of the study area. Four main landform zones were distinguished (from the seashore inwards) and run parallel to the roadway: (A) coastal plain, (B) saline depressions, (C) sand plains and (D) sand dunes. There is a gradual increase in the total number of recorded species in the recognized landform units. Application of TWINSPAN analysis yielded 18 vegetation groups (VG) that comprised 7 main vegetation types (VT). These vegetation types were (I) <i>Artemisia monosperma </i>in the sand dunes, (II) <i>Artemisia monosperma-Echinops spinosus </i>in the sand plains, coastal plain and sand dunes, (III) <i>Cyperus capitatus-Ammophila arenaria </i>in the sand dunes, (IV) <i>Ammophila arenaria-Pancratium maritimum </i>in the coastal plain, (V) <i>Zygophyllum album</i>, (VI) <i>Arthrocnemum macrostachyum </i>and (VII) <i>Arthrocnemum macrostachyum-Zygophyllum album </i>in the saline depressions. Ordination techniques of Detrended Correspondence Analysis (DCA) and Canonical Correspondence Analysis (CCA) were used to examine the relationship between the roadside vegetation and the 8 studied environmental variables: total soluble salts (TSS), pH, calcium carbonate (CaCO_), sand, fine fractions (silt and clay), distance from the seashore (DFS), landform units (LF) and altitude (Alt). Both ordination techniques indicated that soil salinity, calcareous sediments, soil texture, landform, altitude and distance from seashore were the most important factors for the distribution of the vegetation pattern along the road verges in the study area. These gradients were related closely to the first three CCA axes, and accounted for 72.4% of the species relationship among the stands. Low species richness in the vegetation types of the coastal plain and saline depressions may be related to their high soil salinity, while the high species diversity and the highest share of alien weeds of vegetation types characterized the sand dunes may be related to the high disturbance of their substrates as a result of agriculture practising, farming processes and other excessive human disturbances.