The Coastal Desert of Egypt

Abstract

The coastal deserts in Egypt are found along the Mediterranean (east and west), the Red Sea, and the Gulfs of Suez and Aqaba in Sinai Peninsula. The variations in their floristic composition and vegetation structure are varied considerably. The association between the landform units and their floristic features showed significant differences. In the meanwhile, the biological spectrum and chorological analyses of the flora exhibited a general trend in both dominance and structure. Climatic variations, especially rainfall, between the different geographical areas play a profound role in the species distribution patterns. The relationships between the vegetation and the prevailing environmental characteristics indicated the importance of certain soil factors such as coarse and fine sediments, moisture content, electrical conductivity, pH, and organic matter. The distance from the sea and altitude were other significant factors in delimiting species distribution.

The original version of this chapter was revised. An erratum to this chapter can be found at DOI 10.1007/978-3-319-59135-3_14

1 General

Deserts are large bands of dry lands along the tropics in both the Northern and Southern Hemispheres (Mares 1999; Middleton and Thomas 1997). Deserts cover around 25,500,000 km², approximately 20% of the land area of the world. The boundaries of these deserts, which are constantly changing due to various climatic and human factors , are likely to drift over the next century as human-induced global warming takes effect . The defining characteristic of world deserts is aridity. The current UNEP definition of desert is a moisture deficit under normal climatic conditions where P/PET <0.20, i.e. where rainfall is less than 20% of potential moisture loss through evaporation (Smith et al. 1997). The variation among deserts is probably greater than for any other biome, largely because deserts are so widely spaced on the planet and have arisen for very different reasons. North American continental deserts are far hotter and wetter than African and Middle Eastern deserts (Louw and Seely 1982). The Kalahari and Namib deserts in southern Africa mostly experience summer rainfall and are dominated by grasses, while the adjacent succulent Karoo desert experiences winter rainfall and dominated by succulents. In contrast, Middle Eastern deserts experience winter rainfall and are dominated by annual forbs (mostly Asteraceae). The coastal Namibian and Chilean desert systems are driven by fog, while runoff from winter floods controls plant production in Middle Eastern deserts. Australian deserts are limited by phosphorus (Beadle 1981; Stafford Smith and Morton 1990), while nitrogen is the most limiting nutrient in other deserts (Ezcurra 2006).

Desert ecosystems of the world have in recent times been subjected increasingly to untested contacts with humans and their characteristic activities. Within the past 40 years, there has been heavy use of desert scrub communities for land reclamation, recreational purposes, military testing, and different construction projects, all of which have modified physical characteristics of soil and altered the composition of desert scrub vegetation and changing floristic composition.

In Egypt, the desert vegetation is by far the most important and characteristic type of natural plant life . It covers about 95% of the total area of the country and is mainly formed of xerophytic shrubs and subshrubs. Desert vegetation is composed of two sets of plants, ephemerals and perennials . The ephemerals are active only in the vernal aspect of the vegetation. The appearance of ephemerals and the duration of their life are dependent on the chance occurrence of rainy seasons. The perennial plant cover forms the permanent framework of the vegetation and is the best indicator of the habitat condition (Kassas and Imam 1954). Kassas (1966, 1971) added a third type termed accidental vegetation , where precipitation is so low and falls so irregularly that no permanent vegetation exists.

The remarkable variations in the flora and vegetation of its wadi ecosystem and the coastal flora along the Red Sea, the Eastern Desert was of extreme interest to botanists from the early beginnings of the last century such as Schweinfurth (1901), Hassib (1951), Kassas (1952, 1955, 1957 and 1966) Kassas and Batanouny (1984), Hassan (1987), Salama and Fayed (1990), Salama and El-Naggar (1991), Abd El-Ghani (1998), and Hassan (2003). Except that of Schweinfurth (1901) and Hassan (1987), most of the previous studies dealt with different ecological aspects, with less attention to the floristic features of this desert.

During last decades, most of the phytogeographic regions of Egypt (including the Eastern Desert) were affected by human activities such as cultivation of the deltaic part of wadis, the intensive collection of plant species for its values (medicinal, fuel, fibre, etc.), and establishment of new towns, roads, building factories, and quarries. These activities cause a destructive influence in the natural flora and change the distribution of plants in these areas. This means great changes in the distribution, presence, and extinction of the desert plants occurred.

A coastal plain is an area of flat, low-lying land adjacent to a seacoast. One of the world’s largest coastal plains is located in eastern South America. The Mediterranean coast of Egypt (or the Northern coast of Egypt) extends for about 1,050 km from Rafah in the east on Sinai Peninsula to Sallum in the west on the Egyptian–Libyan border . It is one of the longest Mediterranean shores in North Africa. The city of Alexandria lies at the centre of the Mediterranean Egyptian coastline and has been the hub of sea travel between the Mediterranean Sea and the Nile Delta for over 2,300 years.

2 Surveyed Areas

2.1 The Western Mediterranean Coast (Sallum Area)

2.1.1 Association Between Floristic Compositions of Landform Units

The western section of the Mediterranean coastal plain of Egypt extends for about 500 km from Alexandria to Sallum on the Egyptian–Libyan border (Fig. 3.1). It is bounded on the north by the Mediterranean Sea and extends south for an average distance of 50 km, crossing the Northern Plateau (limestone). Physiographically, two main provinces can be distinguished: an eastern province between Alexandria and Ras El-Hikma and a western province between Ras El-Hikma and Sallum (Selim 1969). The southern tableland (Northern Plateau) is mainly covered by stones and gravel and extends southwards to the Qattara Depression . It increases gradually in level westwards and attains a maximum elevation of about 200 m above sea level at Sallum. Northwards it slopes gently to a coastal plain west of Mersa Matruh that varies in elevation from 10 to 30 m above sea level. Eastwards it decreases gradually in level until it loses its line of demarcation with the coastal plain.

Fig. 3.1

Location map of the western Mediterranean coastal land of Egypt (after Hammouda 1982)

Floristically, the Mediterranean coastal land of Egypt represents one of the richest phytogeographical territories of the country. El Hadidi and Hosni (2000) reported that 1,060 species or 51% of the total flora of Egypt are recorded from this territory. Three hundred and twenty-one species are confined in their distribution to a specific habitat and only known from this territory, of which more than two-thirds are typical Mediterranean chorotype . Four plant species are known to be endemic to this territory and not recorded elsewhere in the country; these include Allium mareoticum Bornm. & Gauba, Echinops taeckholmianus Amin, Fumaria microstachys Hausskn., and Helianthemum sphaerocalyx Gauba & Spach (Boulos 1995).

Since the 1950s, much attention has been paid to the western section of the Mediterranean coastal land. Extensive studies on the ecology, flora, biodiversity , phytosociology , and vegetation dynamics are carried out (see Zahran and Willis 1992 for literature). At least ten habitat types are recognized that belong to five vegetation types. These include the desert vegetation, the littoral salt marshes , the coastal dunes, the farmland vegetation, and the aquatic vegetation (for detailed information, see Zahran and Willis 1992; El Hadidi and Hosni 2000). Yet, not all parts of that section have been studied in the same intense way. Till the recent, less attention has been paid to the distant part of the western Mediterranean coast from Sidi Barrani to Sallum on the Egyptian–Libyan frontier . Therefore, floristic investigations were conducted to provide an analysis of the floristic composition associated with different landforms of the Sallum area.

This area represents the distant part of the western Mediterranean coastal land of Egypt, where the human activities through cultivation, grazing , and urbanization are much less pronounced than the other parts of the region. The study area (1,700 km²) lies between 25° 09′–25° 35′E and 31° 32′–31° 15′N and extends for about 49 km from Buqbuq to Sallum on the Egyptian–Libyan frontier (Fig. 3.1). It is included in the semi-desert vegetation zone that is proposed by Bornkamm and Kehl (1990). The coastal plain is very narrow or, sometimes, lacking. Five main landform units can be distinguished in the study area (i.e. from the coast in the north to the fringes of the Diffa plateau in the south; Fig. 3.2): Sallum plateau (U₁), coastal saline depressions (U₂), inland sandy plains (U₃), inland rocky plains (U₄), and shallow wadis (U₅).

Fig. 3.2

Distribution of the 66 sampled sites in the five landform units of Sallum area. U1 Sallum plateau , U2 coastal saline depressions , U3 inland sandy plains , U4 inland rocky plains , and U5 shallow wadis

According to Ayyad and Ghabbour (1986), and recently by El Hadidi and Hosni (2000), the Sallum area lies within the northern arid province that runs parallel to the semiarid belt. Comparing climatic characteristics of four meteorological stations along the western section of the Mediterranean coast, Sallum station, the nearest to the study area, with other three is shown in Table 3.1. The wide variation in annual precipitation along the E–W direction on the Mediterranean coast (from Alexandria in the east to Sallum in the west) is remarkable.

Table 3.1 Long-term annual averages (Courtesy of the Egyptian Meteorological Authority) of some climatic factors of Sallum station in the study area and other three stations along the Mediterranean coast of Egypt

Among the recent advances in geographical methodology and mapping is the technique of geographical information system (GIS) . The study of GIS has emerged in the last decades as an exciting multidisciplinary endeavour, spanning such areas as geography, cartography, remote sensing, image processing, the environmental sciences , and computer sciences. Within computing science, GIS is of special interest of fields such as databases graphics , systems engineering, and computational geometry, being not only a challenging application area but also providing foundational questions for these disciplines.

2.1.1.1 Floristic Composition

A total of 113 species (37 annuals and 76 perennials) belonging to 93 genera and 35 families are recorded. The largest families were Asteraceae and Fabaceae (16 for each), Chenopodiaceae (10), Poaceae (9), Brassicaceae (7), Caryophyllaceae (5), Liliaceae, and Zygophyllaceae (4 for each). They constituted about two-thirds (62.8%) of the recorded species and represent most of the floristic structure in the Mediterranean North African flora (Quézel 1978). Sixteen families are represented by only one species. The largest genera include Astragalus (7), Lotus and Erodium (3 for each), Launaea, Atriplex, Silene, Medicago Limonium, Asparagus, and Asphodelus (2 for each). Though floristic similarities prevail among the different sites of the study area, the floristic composition and vegetation structure show perceptible variations within each site.

Boulos (1975) cited 1,095 species recorded along the Mediterranean coastal region of Egypt. In the present study, the recorded species represent 10.3% of the total flora of the region. It is also noted that the generic index (113/93) is 1.2. Locally, this high ratio is in accordance with Zohary’s (1973) observation “that a striking feature in Egypt’s flora is the large number of genera in proportion to that of the species”. The average global value is 13.6 (Good 1947). This low value in Egypt can be attributed to the lack of accumulation and differentiation centres in Egypt (Zohary 1973).

2.1.1.2 Biological Spectrum

The life-form spectrum of the Sallum area showed that the proportion of therophytes (32.7%) is higher than that of other life forms, while the proportions of chamaephytes (25.7%) and hemicryptophytes (22.1%) are noteworthy. High percentages of therophytes and hemicryptophytes coincide with the floristic characters of the arid zones in the Mediterranean Basin and in general for the floras of arid and semiarid zones (Migahid et al. 1971; Pignatti and Pignatti 1989; Bornkamm and Kehl 1985). The high contribution of annuals may be related to their short life cycles (sometimes a few weeks) that enable them to resist the instability of the arid desert ecosystem of the study area. They also have the ability to set seeds without the need for a visiting pollinator (Baker 1974), and this facilitates the continuity of their life cycles. It is to be noted here that Raunkiaer (1937) suggested a “therophyte climate ” for the Mediterranean climate where a high percentage (>50% of the total species) of therophytes is noteworthy. Raven (1971) pointed out that several Mediterranean floras follow this trend: Cain (1950) in California, Hassib (1951) in Egypt, Zohary (1973) in Palestine, and Quézel (1978) in North Africa.

The distribution of the different life forms in the five landscape units is shown in Table 3.2. Clearly, the shallow wadies had the highest share of annuals. El-Ghareeb and Rezk (1989) provided evidence that therophytes acquire dominance in less saline and sandy habitats, whereas cryptophytes and chamaephyes in more saline habitats in the coastal areas of Egypt. On the other hand, Zahran (1982) concluded that chamaephytes are the most abundant life form in the halophytic vegetation of Egypt. The results of this study are in accordance with these findings. It is of interest to note that the proportions of cryptophytes , hemicryptophytes , and chamaephytes constitute the main bulk of the floristic structure in each of the five geomorphologic units . It ranges between 50% in the shallow wadis and 73.4% in the rocky plains, where they seem to play an important role in the process of sand accumulation and succession of vegetation in the study area. Plants of these three life forms have the ability to act as barriers to wind- and/or water-borne materials, which are then deposited around them. This enables such plants to produce adventitious roots and aerial shoots from their buried organs and to replace them when they die. This has also been noted along the Mediterranean coast of Egypt (Batanouny 1973; Khedr 1993).

Table 3.2 Numbers and percentages of the life forms represented in the geomorphologic landscape units in the study area

Pearson’s product–moment correlations between the floristic compositions in the different landform units (U₁–U₅) were demonstrated in Table 3.3. Apart from the shallow wadis (H₅), positive significant differences between the other units were remarkable. The coastal saline depressions and the inland sandy plains showed negative correlations with the shallow wadis .

Table 3.3 Pearson’s product–moment correlations between the five landform units (U₁–U₅) of the Sallum area

2.1.1.3 Chorological Affinities

Results of the chorological analysis (Table 3.4) revealed that 45.2% of the studied species were uniregional, of which 23% being native to the Saharo–Arabian chorotype . The typical Mediterranean was ranked second (21.3%), while the Sudano–Zambezian chorotype was very modestly represented. About 50.4% of the recorded species were biregional and pluriregional, extending their distribution all over the Saharo–Arabian, Sudano–Zambezian, Irano–Turanian , Mediterranean, and Euro–Siberian chorotypes. Being part of the Mediterranean region, the Mediterranean chorotype (uni, bi, and pluri) constituted 55.7% of the recorded species, whereas the Saharo–Arabian constituted 38.9%. Thus, they formed the major components (94.6%) of the floristic composition in this study. The biregional Mediterranean and Irano–Turanian chorotypes constituted the highest values (11.5%, 11.5%, and 9.7%, respectively). These results are in agreement with the findings of White (1993a, b), who claimed that the study area lies within the Mediterranean/Sahara regional transition zone, where the vegetation comprises floristic elements for both of the Mediterranean and Saharo–Arabian regions .

Table 3.4 Chorotype analysis of the species examined as numbers (N) and percentages (%) of the total species recorded

Distribution of the major chorotypes in the five landform units (Fig. 3.3) indicated the decrease in the numbers of the Mediterranean species in the Sallum plateau and Saline depressions and the increase of the Saharo–Arabian species in the inland rocky plains and the shallow wadis . This may be attributed to the fact that plants of the Saharo–Arabian region are good indicators for desert environmental conditions, while Mediterranean species stand for more mesic environment. A checklist of the included species occurring in the study area, together with their distribution in the different landform units and chorotypes , was shown in Table 3.5.

Fig. 3.3

Distribution of the major chorotypes in the five landform units of the Sallum area

Table 3.5 Distribution of plant species recorded in the Sallum area, together with their life forms and chorotypes in the five landform units (U₁–U₅). For abbreviations of life form and landform units, see Table 3.2

2.1.1.4 Species Distribution Patterns (Figs. 3.4, 3.5, 3.6, 3.7, and 3.8)

Nine of the recorded species were ubiquitous, have a wide ecological range of distribution, and represented in all the five landform units. Psammophytes (e.g. Deverra tortuosa, Thymelaea hirsuta, Haloxylon salicornicum, Anabasis articulata) and halophytes (e.g. Atriplex halimus, Atriplex portulacoides) have the highest presence values (P = 100%). On the other hand, Carthamus glaucus showed the highest presence estimate among annuals (P = 100%). Sixty-one species or about 53.9% of the recorded flora demonstrated a certain degree of consistency, where they exclusively recorded in or confined to a certain landform unit and do not penetrate elsewhere. In the Sallum plateau , Euphorbia dendroides and Artemisia judaica were recorded. The former species is considered by El Hadidi et al. (1992) as one of the endangered species known from Sallum area and represents its westernmost range of distribution. It is a very rare species that confined to the Marmarica district of the Mediterranean coastal land of Egypt (El Hadidi and Fayed 1978). El-Garf (2003) reported that wadi Halazeen (west of Mersa Matruh) is a less known natural habitat that supports a dense growth of Euphorbia dendroides . Urgent conservation measures should be taken for this species in its natural habitat.

Fig. 3.4

Distribution map of Thymelaea hirsuta (up) and Asphodelus ramosus (down)

Fig. 3.5

Distribution map of Halocnemum strobilaceum (up) and Limoniastrum monopetalum (down)

Fig. 3.6

Distribution map of Pancratium maritimum (up) and Retama raetam (down)

Fig. 3.7

Distribution map of Periploca angustifolia (up) and Peganum harmala (down)

Fig. 3.8

Distribution map of (up) and Globularia arabica (up) and Gymnocarpos decanter (down)

In the coastal saline depressions , where halophytic vegetation dominates, nine species were recorded. Arthrocnemum macrostachyum, Halocnemum strobilaceum, Frankenia revoluta, Ammophila arenaria, and Limoniastrum monopetalum were the dominants. These species comprised the common salt marsh plant communities in the western Mediterranean region of Egypt (Shaltout and El-Ghareeb 1992). Heavy deposition of sand and the active formation of hummocks by the sand binding character of the dominant plants may contribute to the instability of its environment.

Forty-one species were confined to the shallow wadis , of which 21 were annuals. This landform is known to be the richest among the others. It represents one of the major physiographic features of the western Mediterranean desert of Egypt, with peculiar physical and biological features including a characteristic plant cover. Some of these wadis are vegetationally and floristically rich and used mainly as rangelands (Kamal 1988). The phytosociology and vegetation analyses of some of these wadis were the subject of El Hadidi and Ayyad (1975) and extended by El-Kady and Sadek (1992) and Kamal and El-Kady (1993). Among the recorded species, Anthemis microsperma, Brassica tournefortii, Malva parviflora, Trigonella stellata, Cutandia memphitica, and Reichardia tingitana were included.

Three species from the inland sandy plains and other six from the inland rocky plains were recorded. The latter landform unit favours the growth of certain chasmophytes, e.g. Globularia arabica and Noaea mucronata. Three species are common in both landform units: Herniaria hemistemon, Heliotropium lasiocarpum, and Gymnocarpos decanter.

2.1.2 Vegetation Analysis and Environmental Relationships

2.1.2.1 Classification of the Vegetation

The application of TWINSPAN on the relative importance values (IV) of the 55 perennial species recorded in 53 sampled stands helped to distinguish five vegetation groups (Fig. 3.9, Table 3.6). These groups were named after their leading dominant species (those have the highest relative IV) as follows: (A) Haloxylon salicornicum, (B) Haloxylon salicornicum–Thymelaea hirsuta, (C) Thymelaea hirsuta–Anabasis articulata, (D) Haloxylon salicornicum–Atriplex portulacoides, and (E) Salsola tetrandra–Limoniastrum monopetalum. Each of these groups could easily be linked to a habitat type : foot of the Diffa plateau , sand plains, nonsaline depressions, saline depressions, and the coastal salt marshes , respectively. Table 3.7 summarizes the mean values and the standard deviations of the measured soil variables and the diversity indices in the five groups derived from TWINSPAN .

Fig. 3.9

TWINSPAN dendrogram of the 53 studied stands of the Sallum area based on their importance values . A–E are the five vegetation groups

Table 3.6 Species composition of the 53 stands in the six transects, arranged in order of occurrence in the five TWINSPAN groups (A–E). The mean importance value (out of 300) rounded to the nearest integer is given in each group

Table 3.7 Mean values and standard deviations (±) of the soil variables in the stands representing the vegetation groups obtained by TWINSPAN

The first TWINSPAN dichotomy differentiated the 53 stands into two main groups according to pH, EC, Na⁺, K⁺, and Mg⁺⁺ (p = 0.0001). Group E (12 stands) dominated by Salsola tetrandra–Limoniastrum monopetalum, which inhabited the coastal saline depression , was separated on the right side of the dendrogram , while the left side is still heterogeneous (Fig. 3.9). At the second hierarchical level , the inland dry group of stands (41) was split into two subgroups related to pH, EC, organic matter, Na⁺, and altitude (p = 0.0001). Here, another distinct group (A; 9 stands) dominated by Haloxylon salicornicum found on the gravel plains at the foot of Diffa plateau was also separated. Description of each group will be given below.

Group A. Haloxylon salicornicum Group

The nine stands of this group were sampled from the foot of the Diffa plateau . On the highly elevated and gravely calcareous soil with moderate moisture content and the least amounts of organic matter and salinity (Table 3.6), sand sheets of Haloxylon salicornicum were found. It was differentiated by the growth of shrubs of Retama raetam, Lycium europaeum, and Farsetia aegyptia and occupied parts of the drainage channels of the southern stretches where surface deposits were deeper. This group had the largest share (23) of annuals. Shortly after rainfall, the soil surface supporting the sites of this group was covered with a dense vegetation of annual species, especially Schismus barbatus, Anthemis microsperma, Reichardia tingitana, Brassica tournefortii, Medicago laciniata, Cutandia memphitica, Erodium pulverulentum, Malva parviflora, and Astragalus hamosus .

Group B. Haloxylon salicornicum–Thymelaea hirsuta Group

The landscape of this group was characterized by a combination of Haloxylon salicornicum and Thymelaea hirsuta found on the sand plains with deep loose soil and the lowest levels of moisture content. It represents a transitional zone between the nonsaline and saline depression vegetation groups. This group was differentiated by a number of woody species such as Periploca angustifolia, Deverra tortuosa, Globularia arabica, and Zilla spinosa. The herb layer was relatively sparse and characterized by Hordeum leporinum, Asphodelus tenuifolius, Bupleurum lancifolium, and Astragalus peregrinus. The most common xerophytic species in the Egyptian Desert, Sinai, and the neighbouring arid environments were included in this group (Zohary 1973; Batanouny 1979a; Salama and Fayed 1990; Abd El-Ghani and Amer 2003) .

Group C. Thymelaea hirsuta–Anabasis articulata Group

This vegetation group dominated the nonsaline depressions with soils of the highest pH values and the lowest levels of carbonate content. Other physical soil properties were comparable to those of group B. While Gymnocarpos decandrum, Asphodelus ramosus, and Astragalus siberii dominated the shrub layer , the herb layer showed the lowest share of annuals (viz. Centaurea glomerata, Lotus angustissimus, Asphodelus tenuifolius, and Hordeum leporinum) .

Group D. Haloxylon salicornicum–Atriplex portulacoides Group

This was the largest group of stands (13) and the most diversified among the other vegetation groups. It inhabited the saline depressions on fertile soils that are rich in their fine sediment contents (silt and clay). Relatively high soil salinity favoured the growth of some salt-tolerant species as Atriplex portulacoides, Salsola tetrandra, and Nitraria retusa. The shrub layer was characterized by the growth of Carthamus glaucus, Anabasis articulata, Carduncellus mareoticus, and Deverra tortuosa. Other species showed certain degree of fidelity since they did not penetrate to other vegetation groups: such as Helianthemum lippii, Noaea mucronata, and Verbascum letourneuxii. Few annual species Bassia muricata, Astragalus hamosus, Centaurea glomerata, and Asphodelus tenuifolius were recorded .

Group E. Salsola tetrandra–Limoniastrum monopetalum

On muddy fertile saline soil with high Na⁺, K⁺, and Mg⁺⁺, the coastal salt marshes with vegetation characterized by the complex Halocnemum strobilaceum, Salsola tetrandra, and Limoniastrum monopetalum were found, indicating the saline nature of this group (12 stands). Notably, several halophytic species were recorded such as Suaeda maritima, Arthrocnemum macrostachyum, Zygophyllum album, Frankenia hirsuta, and Limonium pruinosum. The herb layer was modestly represented and included among others Brassica tournefortii, Centaurea glomerata, Astragalus hispidulus, and Hordeum leporinum .

2.1.2.2 Soil Characteristics of the Vegetation Groups

Environmental characteristics of the five vegetation groups were summarized in Table 3.7. Of the measured parameters, clay, organic matter, pH, electric conductivity, altitude, Na⁺, K⁺, and Mg⁺⁺ showed highly significant differences between groups. It can be noted that clay, moisture content, electric conductivity, K⁺, and Mg⁺⁺ displayed relatively high values on coastal salt marshes (group E), organic matter on the saline depressions (group D), and total carbonates and altitude on the foot of Diffa plateau (group A). A remarkable decrease in salinity gradient from the coastal salt marshes (group E) to the foot of Diffa plateau (group A) is also noticeable.

2.1.2.3 Ordination of Stands

Figure 3.10 showed the ordination results of the DCA analysis of the floristic data set. The 53 stands were plotted along axes 1 and 2 and tend to cluster into five groups that resulted from TWINSPAN analysis described above. The stands were spread out 6.4 SD units along the first axis (eigenvalue = 0.81), expressing the high floristic variations among vegetation groups and indicating a complete turnover in species composition that took place (Hill 1973). This diagram displayed graphically that group B was transitional in its composition between the other groups. Stands of group E were separated towards and the positive end of DCA axis 1, while those of groups A and C were separated out along the other end. DCA axis 2 with an eigenvalue of 0.53 and a gradient length of 3.86 SD is less important. The species–environment correlation (Table 3.8) was also high: 0.83 and 0.55 for DCA axis 1 and 2 showing that the species data were related to the measured environmental variables. The significant correlations of soil variables with the first three DCA axes revealed greater correlations along axis 1 than the higher-order axis. DCA axis 1 showed significant correlations with altitude, EC, K⁺, moisture content, and clay, which can be interpreted as an altitude–soil salinity gradient . As axis 2 was significantly correlated with total carbonates and altitude, which was interpreted as an altitude–carbonate gradient .

Fig. 3.10

DCA ordination diagram for the 53 stands on the first two axes with the TWINSPAN groups superimposed

Table 3.8 Comparison of the results of ordination for the first three axes of DCA and CCA . Intra-set correlations of the soil variables, together with eigenvalues and species–environment correlation coefficients. For soil factors abbreviations and units , see Table 3.7

2.1.2.4 Environment–Vegetation–Diversity Relationships

The successive decrease of the eigenvalues of the first three CCA axes (Table 3.8) suggests a well-structured data set. These eigenvalues were somewhat lower than for the DCA axes , indicating that important explanatory stand variables were not measured and included in the analysis or some of the variations were not explained by environmental variables (Franklin and Merlin 1992; McDonald et al. 1996). However, the species–environment correlations were higher for the first three canonical axes, explaining 67.3% of the cumulative variance. These results suggested a strong association between vegetation and the measured soil parameters presented in the biplot (Jongman et al. 1987). From the intra-set correlation of the soil factors with the first three axes of CCA shown in Table 3.8, it can be noted that CCA axis 1 was correlated to clay, moisture content, pH, EC, K⁺, and altitude. This fact becomes more clearly in the biplot (Fig. 3.11). A test for significance with an unrestricted Monte Carlo permutation test (99 permutations) found the F-ratio for the eigenvalue of axis 1 and the trace statistics to be significant (p < 0.001), indicating that observed patterns did not arise by chance. CCA axis 2 was clearly related to pH, Mg⁺⁺, and altitude .

Fig. 3.11

CCA biplot of axes 1 and 2 showing the distribution of the 53 stands with their TWINSPAN groups and soil variables

3 Concluding Remarks

• 1. The plant life was restricted to microenvironments (as in wadis, runnels, and depressions) where runoff water collects and provides sufficient moisture for plant growth. This was described by Monod (1954) as végétation contracté, runoff desert (sensu Zohary 1962), and restricted desert (sensu Walter 1963). The vegetation was characterized by sparseness of plant cover (does not exceed 5% on the average; Kassas 1966), a limited number of plant species (12 on the average in each stand), and paucity of trees (5% of the recorded species). Therophytes , chamaephytes , and hemicryptophytes constituted the mean bulk (80.1%) of the recorded species. High percentages of therophytes and hemicryptophytes coincide with the floristic characters of the arid zones in the Mediterranean Basin and in general for the floras of arid and semiarid zones (Migahid et al. 1971; Bornkamm and Kehl 1985; Pignatti and Pignatti 1989).

• 2. According to White and Léonard (1991), this area lies in the Mediterranean–Sahara regional transition zone that includes the coastal land along the Mediterranean Sea. Chorological analysis of species showed the decrease in the numbers of the Mediterranean species and increase of the Saharo–Arabian species along N–S direction form the seashore inwards till the fringes of Diffa plateau . This may be attributed to the fact that plants of the Saharo–Arabian region are good indicators for desert environmental conditions, while Mediterranean species stand for more mesic environment. Being part of the Mediterranean region, the Mediterranean chorotype (uni, bi, and pluri) constituted more than 50% of the total flora, while the Saharo–Arabian chorotype constituted 38.9%. This result is in agreement with the findings of White (1993), where the vegetation comprises floristic elements of both Mediterranean and Saharo–Arabian regions .

• 3. Phytosociological investigations indicated that Haloxylon salicornicum, Thymelaea hirsuta, and Anabasis articulata dominated the vegetation. The next important species were Atriplex portulacoides, Salsola tetrandra, Deverra tortuosa, Asphodelus ramosus, and Halocnemum strobilaceum; each exerted a local dominance in certain stands than in others. Nevertheless, these species were so overlapping in their phytosociological behaviour that no distinct association could be recognized, and accordingly, the vegetation may be considered as a continuum that could be a part of a larger vegetational gradient in the Western Desert of Egypt. This, however, does not preclude the possibility of classifying it into different vegetation groups.

• 4. The vegetation of the Sallum area was differentiated into two main parts: coastal dominated by halophytic plant communities and inland desert dominated by xerophytic ones. The application of TWINSPAN revealed the separation of five distinct vegetation groups named after their dominant species as follows: Haloxylon salicornicum (A), Haloxylon salicornicum–Thymelaea hirsuta (B), Thymelaea hirsuta–Anabasis articulata (C), Haloxylon salicornicum–Atriplex portulacoides (D), and Halocnemum strobilaceum–Salsola tetrandra–Limoniastrum monopetalum (E). Most of these species have repeatedly been recorded as abundant in ecological studies of specific habitats in the western Mediterranean coastal land of Egypt (Tadros and Atta 1958; Migahid et al. 1971; Ayyad and El-Ghareeb 1982; Shaltout and El-Ghareeb 1992; Zahran et al. 1996), and variations in their abundances have also been related to edaphically and topographic variations (Abdel-Razik et al. 1984; El-Ghareeb and Hassan 1989; El-Kady and Sadek 1992). The floristic composition, therefore, represents most of the floristic structure in the Mediterranean North-African flora (Quézel 1978).

• 5. The vegetation groups that resulted from TWINSPAN may be related to the Salsolion tetrandrae of habitats with soils derived from chalky rocks and marls and rich in lime and soluble salts (Zohary 1973) and the Anabasion articulatae arenarium, Hammada-Anbasion articulatae, and Thymelaeion hirsutae (Tadros and Atta 1958) of less saline habitats. The associations belonging to these alliances with their characteristic species have been described by Maire and Weiller (1947), Killian and Lemée (1948), Braun-Blanquet (1949), Simmoneau (1954), and Navikoff (1961) in North Africa and by Tielbörger (1997) in Sinai and in the Negev Desert of Israel. However, Bornkamm and Kehl (1990) suggested one new order, Pituranthetalia tortuosi, to comprise all the plant communities of the Western Desert of Egypt. Consequently, the vegetation of this area represents a transition from the western communities in North Africa to those characteristics of eastern Mediterranean. Ayyad and El-Ghareeb (1982) and El-Ghareeb (1990) have reported similar conclusion in the salt marsh vegetation along the western Mediterranean coast of Egypt.

• 6. Both DCA and CCA assessed the soil–vegetation relationships. The results of CCA analysis showed well the relative positions of species and sites along the most important ecological gradients. Both ordination techniques clearly indicated that fine soil sediments, moisture content, pH, electric conductivity, altitude, and relative concentrations of K⁺ and Mg⁺⁺ were the most important parameters for the distribution of the vegetation pattern in this area. The role of these factors in delimiting plant communities in the Western Desert has been stressed by many authors, among others Ayyad (1976) and Kamal and El-Kady (1993). The percentage of surface sediments of different size classes determines the spatial distribution of soil moisture (Yair and Danin 1980), as shown for other desert ecosystems in Egypt by Sharaf El Din and Shaltout (1985) and Abd El-Ghani (1998, 2000a) and in Saudi Arabia by El-Demerdash et al. (1994).

• 7. The distribution of species in saline and marshy habitat which relates to salinity in many arid regions has been discussed by several authors, Kassas (1957), Ungar (1968), and Maryam et al. (1995), among others. Ungar (1974) indicated that the distribution of halophytes in the United States is mainly dependent on the salinity gradient , while local climate, topography, soil moisture, and biotic factors are less important. Ragonese and Covas (1947) described the interrelation of the salinity gradient and vegetation in the northern Argentinian salt marshes . Abu-Ziada (1980) and Abd El-Ghani (2000b) also noted strong relationships between the vegetation pattern and the soil moisture–salinity gradients in the oases of the Western Desert of Egypt. When studying the salt marsh communities of the western Mediterranean coastal desert, Ayyad and El-Ghareeb (1982) pointed out that salinity, the concentration of different ions, and the periodical variation in the water table determine the distribution of species and the differences between communities. They also conclude that the salt marsh vegetation in this part of the country represents a transition from the western communities in North Africa and those characteristics of the Eastern Mediterranean region. In their account of the northern and eastern Mediterranean coastal salt marshes , Zahran et al. (1996) demonstrated the distribution of some halophytic species as best correlated along a gradient of a dozen of soil variables, the most important are salinity, moisture content, soil texture, organic matter, and calcium carbonate. In this area, the gradient in soil salinity and its variation from one habitat to another is the primary determinant of the plant community composition.

3.1 The Eastern Mediterranean Coast (El-Arish-Rafah Area)

It is located between El Arish (31° 10′N, 33° 48′E) and Rafah (31° 17′N, 34° 15′E) and extends for about 45 km along the northeastern Mediterranean coast of Sinai (Fig. 3.12). The area was chosen for its high environmental diversity. It represents the easternmost part of the international coastal highway that links Egypt with the countries of North Africa in the west and those of the eastern Mediterranean in the east. The natural vegetation is very sparse. A semi-steppe type of vegetation characterizes the study area. Kassas (1952) reported the major dominant landforms (littoral dunes, inland dunes, and salt marshes ), but Danin (1983) listed further floristic subdivisions and brief habitat descriptions. The coastal belt of the sand dunes represents one of the salient features of the investigated area. The dunes of north Sinai absorb and store rainwater, the lowlands between them being a permanent source of fresh water that can be tapped by digging shallow wells. As a result of population pressure, the demand for fresh-water supplies was accordingly increased. Thus, water from the Nile is now transferred to Sinai Peninsula through El Salam Canal.

Fig. 3.12

Location map showing El-Arish-Rafah area

Desert reclamation and agricultural processes were practiced in the study area. Date palm plantations and irrigated gardens are other conspicuous features along part of the seashore. In many instances, the land was ploughed and cultivated after the first rain of a season.

Cultivation of barley, maize, tomato, sesame, grapes, peaches, pomegranates, olives, figs, and watermelons was achieved. Nevertheless, spreader dykes were also conducted for cultivation of beans and wheat, and other cereals were carried out just upstream of the dykes. Large-scale forestation with tamarisk (Tamarix aphylla) and Acacia saligna was carried out, mainly along roads traversing the dunes, to arrest sand dune encroachment (Weinstein and Schiller 1979).

According to UNESCO-FAO (1963), the climate of the study area is attenuated subdesertic . Recent records of climatic data for Rafah were incomplete and insufficient. Available records of the mean annual rainfall decrease in the east–west direction. It reached c. 304 mm year ⁻¹ at Rafah and 96.8 mm at El Arish. The gradient in the annual rainfall is obvious, which was associated with an inverse evaporation gradient, indicating the increase of aridity from west of the study area to its east. Average daily maxima of the hottest month were 38.6 °C at El Arish and 31.5 °C at Rafah, while average daily minima of the coldest month were 7.3 °C and 7.8 °C, respectively. Frost may occur in January and February at El Arish, and fog and dew were also common and probably contribute much to the total sum of plant-available moisture. Average maximum relative humidity at El Arish was 70%, and the average minimum was 32%.

4 Floristic Relations

In total , 78 species from 31 families of the vascular plans were found, of which 24 annuals and 54 perennials. There is a gradual increase in the total number of recorded species from 27 in the coastal plain to 43 in the sand dunes . The floristic similarities between the recognized four landforms (Table 3.9) showed significant positive correlations between saline depressions and the coastal plain in one hand and between the sand plains and sand dunes in the other. The coastal and sand plains were negatively correlated with each other. Regarding species richness, the floristic composition in the recognized landforms showed remarkable differences. Chamaephytes were the predominant life form and constituted 32% of the recorded flora, followed by therophytes (31%) and hemicryptophytes (17%). In this context, chamaephytes, hemicryptophytes, and cryptophytes altogether constituted the main bulk of the floristic structure of each of the recognized landform unit. It ranged from 49% and 51% in sand dunes and sand plains to 61% and 67% in the coastal plain and saline depressions, respectively.

Table 3.9 Sørensen’s coefficient of floristic similarity (CCs) between the different landform units in the study area

None of the 78 species occurs at all the 63 studied stands. There were few highly frequent species and very many that were infrequent. Only 2 species (Echinops spinosus and Zygophyllum album) had a frequency of more than 50%, and 35 species (about 65% of the total) had a frequency more than 10%. This is similar to the distribution of frequencies reported for roadside vegetation in California (Frenkel 1970) and New Zealand (Ullmann et al. 1995). Some of the recorded species have wide ecological and sociological range of distribution such as Cornulaca monacantha and Cyperus capitatus , with 75 records and the highest occurrence among perennials (24%), while Mesembryanthemum crystallinum recorded in 119 sample plots and showed the highest occurrence among annuals (38%).

The results revealed that 37 species (55.2% of the total) demonstrated a certain degree of consistency, where they exclusively recorded in or confined to a certain landform unit and do not penetrate elsewhere. These species were distributed as follows: 11 in the sand plains (e.g. Panicum turgidum, Fagonia arabica, and Convolvulus lanatus), 3 in the coastal plain (e.g. Agathophora alopecuroides, Solanum elaeagnifolium, and Euphorbia paralias), 13 in the saline depressions (e.g. Arthrocnemum macrostachyum, Juncus rigidus, Halocnemum strobilaceum, and Suaeda aegyptiaca), and 10 in the sand dunes (e.g. Cynodon dactylon, Bassia indica, Chenopodium murale, Amaranthus graecizans, and Rumex pictus).

5 Vegetation Classification

Classification of the presence–absence data set of 78 species recorded in 63 stands using the TWINSPAN analysis yielded 18 vegetation groups (VG) at level 6 of the hierarchy (Fig. 3.13; Table 3.10). These groups could be categorized at level 3 of the classification into seven major vegetation types (VT) . These types were named after the first and second dominant species as follows: (I) Artemisia monosperma in the sand dunes ; (II) Artemisia monosperma–Echinops spinosus in the sand plains, coastal plain, and sand dunes ; (III) Cyperus capitatus–Ammophila arenaria in the sand dunes; (IV) Ammophila arenaria–Pancratium maritimum in the coastal plain; (V) Zygophyllum album; (VI) Arthrocnemum macrostachyum; and (VII) Arthrocnemum macrostachyum–Zygophyllum album in the saline depressions. One-way ANOVA test showed significant differences (F-ratio = 8.8; p = 0.001) between the recognized landforms and the evolved vegetation types. The total number of recorded species and species richness of the seven vegetation types (VT) differs between stands (Table 3.10). While VT (II) had the highest total number of species (56), VT (III) and (V) had the lowest (13 and 14, respectively). The highest species richness of 16.7 ± 4.8 was found in VT (II), but the lowest (6.9 ± 2.2) was in VT (IV).

Fig. 3.13

The dendrogram resulting from TWINSPAN analysis of 63 stands of the study area. The broken line denotes the level at which the dendrogram yields seven vegetation types (I–VII). Indicator species and vegetation group abbreviations are shown in the Appendix

Table 3.10 Characteristics of the seven vegetation types (VT) and 18 vegetation groups (VG) derived after the application of TWINSPAN . For landform unit abbreviations, see Table 3.9

Characteristics of the vegetation groups showed that 17 out of the 18 groups occurred only in one landform, while VG (7) dominated by Artemisia monosperma was represented in the sand plains and the sand dunes . Whereas the vegetation groups of Ammophila arenaria–Pancratium maritimum and Echinops spinosus–Artemisia monosperma have the highest species richness (16.5 ± 1.5 and 16.2 ± 2.4, respectively species), those of Artemisia monosperma–Ammophila arenaria (5.2 ± 1.7), Artemisia monosperma–Zygophyllum album, and Arthrocnemum macrostachyum–Frankenia hirsuta (6.0 ± 2.0 for each) had the lowest.

5.1 Abbreviations of Indicator Species

Species	Abbreviation
Ammophila arenaria (L.) Link	Ammo
Arthrocnemum macrostachyum (Moric.) K.Koch	Arth
Bassia indica (Wight) A.J. Scott	Bass
Cleome amblyocarpa Barratte & Murb.	Cleo
Cornulaca monacantha Delile	Corn
Echinops spinosus L.	Echi
Elymus farctus (Viv.) Runemark ex Melderis	Elym
Moltkiopsis ciliata (Forssk.) I.M. Johnst.	Molt
Pseudorlaya pumila (L.) Grande	Pseu
Stipagrostis scoparia (Trin. & Rupr.) de Winter	Stip
Zygophyllum album L.f.	Zygo

5.1.1 Abbreviations of Vegetation Groups (VG)

Landform unit abbreviations: C, coastal plain; S, sand plain; M, saline depressions; and D, sand dunes

(VG)	Species	Abbreviations
1	Ammophila arenaria–Artemisia monosperma	Am–Ar
2	Artemisia monosperma	Ar
3	Artemisia monosperma–Zygophyllum album	Ar–Z
4	Pancratium maritimum–Thymelaea hirsuta	P–T
5	Thymelaea hirsuta–Silene succulenta	T–S
6	Artemisia monosperma–Echinops spinosus	Ar–Ec
7	Artemisia monosperma	Ar
8	Artemisia monosperma–Cleome amblyocarpa	Ar–Cl
9	Artemisia monosperma–Echinops spinosus	Ar–Ec
10	Ammophila arenaria–Cyperus capitatus	Am–Cy
11	Ammophila arenaria	Am
12	Ammophila arenaria–Pancratium maritimum	Am–P
13	Ammophila arenaria–Tamarix nilotica	Tm–Am
14	Zygophyllum album	Z
15	Arthrocnemum macrostachyum	Arth
16	Zygophyllum album–Arthrocnemum macrostachyum	Z–Arth
17	Zygophyllum album–Juncus rigidus	Z–J
18	Arthrocnemum macrostachyum–Frankenia hirsuta	Arth–F

A Detrended Correspondence Analysis (DCA) ordination plot of the 63 stands on axes 1 and 2 (Fig. 3.14), with the 7 TWINSPAN vegetation types , was superimposed. The stands were spread out at 5.3 SD units of the first axis (eigenvalue = 0.71), expressing the high floristic variation among the vegetation types and indicating a complete turnover in species composition that took place (Hill 1979). Stands of VT (I) were separated towards the positive end of DCA axis 1, while those of VT (VII) were separated out along the other end. DCA axis 2 with eigenvalue of 0.39 and a gradient length of 3.11 was less important. The species–environment correlation was high: 0.96 and 0.67 for DCA axes 1 and 2, showing that the species data were strongly related to the measured environmental variables. A well-defined gradient in soil salinity (r = −0.92) was found on axis 1, reflected in the species composition from stands with high to stands with low saline content. The vegetation types (V), (VI), and (VII) of the saline depressions appeared on the left side of axis 1, while those of other landforms appeared on the right side. Plot scores of DCA axis 2 were positively correlated (r = 0.61) with landform, indicating a gradient from coastal plain on the seashore to sand dunes inwards in the desert .

Fig. 3.14

Ordination diagram of Detrended Correspondence Analysis (DCA) of 63 stands, with their TWINSPAN vegetation types

6 Vegetation–Environment Relationships

The soil variables of the stands comprising the seven vegetation types differ significantly according to the one-way ANOVA (Table 3.11). The soil of VT (I) had the highest content of sand, but the lowest content of clay, CaCO₃, and total soluble salts. The soil of VT (II) had the highest content of CaCO₃, while the soil of stands which constitute VT (III) had the lowest silt content (0.9%), the farthest from the seashore (193.3 m) and at the highest altitudes (36.7 m above sea level). The soil of VT (IV) occupies the lowest altitude (8.1 m above sea level) that was very close to the seashore (DFS = 21.9 m) and rich in clay content (7.9%). The soils of VT (V), (VI), and (VII) have the highest values of salinity (18.1, 24.5, and 41.9 meq/l, respectively) .

Table 3.11 Mean values, standard deviation (± SD), and ANOVA F-values of the environmental variables and species richness in the stands representing the seven vegetation types (I–VII) obtained by TWINSPAN

The species–environment correlations were higher for the first three canonical axes, explaining 72.4% of the cumulative variance (Table 3.12). These results suggest a strong association between vegetation and the measured environmental parameters presented in the biplot (Jongman et al. 1987). From the intra-set correlations of the environmental variables and the first three axes of CCA, it can be inferred that CCA axis 1 was positively correlated with salinity and negatively with altitude, while CCA axis 2 was defined by landforms, distance from the seashore, altitude,` and clay. This fact becomes evident in the ordination biplot (Fig. 3.15). Contributions of salinity, landforms, altitude, and clay, which were selected by the forward selection option in the program CANOCO , to the variation in species data, were 36.8%, 17.2%, 14.4%, and 6.9%, respectively. A test for significance with an unrestricted Monte Carlo permutation test found the F-ratio for the eigenvalue of CCA axis 1 and the trace statistics to be significant (p = 0.01), indicating that the observed patterns did not arise by chance. The ordination diagram produced by CCA in Fig. 3.15 showed that the pattern of ordination was similar to that of the floristic DCA (Fig. 3.14), with most of the stands remaining in their respective TWINSPAN vegetation types . Clearly, vegetation types (V), (VI), and (VII) were highly associated with soil salinity, those of VT (I) and (III) with altitude and the distance from the seashore, and those of VT (II) and (IV) with clay and lime content .

Table 3.12 Comparison of the results of ordination for the first three axes of DCA and CCA . Intra-set correlations of the environmental variables, together with eigenvalues and species–environment correlation coefficients

Fig. 3.15

Ordination biplot yielded by canonical correspondence analysis (CCA) of the 63 stands with their TWINSPAN vegetation types and soil variables

7 Diversity Versus Environment

The effects of environmental variables on the species richness were shown in Table 3.13. The results showed that species richness was significantly correlated with the first axis (salinity–altitude gradient) of CCA ordination, but was unrelated to the second axis (landform CaCO₃ gradient). Whereas soil salinity exhibited high significant negative correlation with species richness (p = 0.001), landforms were positively correlated with it (p = 0.001).

Table 3.13 Spearman rank correlations between species richness and stand scores of the first two axes of CCA and the environmental variables

8 Concluding Remarks

• 1. The examined the vegetation–environment relationships in the different landforms along the roadside verges between El Arish and Rafah on the northeastern Mediterranean coast of Sinai. Both DCA and CCA were applied to assess the species distribution and the prevailing environmental conditions. The results of CCA showed well the relative positions of species and stands along the most important ecological gradients. 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. The distribution of the vegetation types reflects these relations, with VT (V–VII) being typical of the saline silty stands, VT (I and III) and partly VT (II) showing a gradient of increasing altitude and distance from seashore, and VT (IV) and mostly VT (II) being found on more CaCO₃ and clay contents.

• 2. The 18 groups identified by TWINSPAN were considered to represent seven vegetation types, each of definite floristic and environmental characteristics . Most of the characteristic species of the identified vegetation types were salt-tolerant species, indicating the saline nature of the study area. The application of DCA to the same set of data supports the distinction between these types. Some of the identified vegetation types have very much in common with that recorded along the western Mediterranean coastal land (Shaltout and El-Ghareeb 1992), in south Sinai region (El-Ghareeb and Shabana 1990; Abd El-Ghani and Amer 2003), in some wadis of the Eastern (Fossati et al. 1998) and Western Desert (Bornkamm and Kehl 1985; Abd El-Ghani 2000a), and in the Negev Desert of Israel (Olsvig-Whittaker et al. 1983; Tielbörger 1997). Due to the specific environment of the study area, many species with a nitrophilous (e.g. Cynodon dactylon, Cakile maritima, and Phragmites australis), psammophilous (e.g. Echinops spinosus, Cornulaca monacantha, Cyperus capitatus, and Artemisia monosperma), halophilous (e.g. Arthrocnemum macrostachyum, Halocnemum strobilaceum, Agathophora alopecuroides, Juncus rigidus, and Frankenia hirsuta), and psammohalophilous (e.g. Zygophyllum album, Ammophila arenaria, and Tamarix nilotica) occurred in the distinguished vegetation types.

• 3. It has been emphasized that roadside zonation was based on structural criteria , such as vegetation height, density, and dominance structure of plant communities rather than on floristic composition only (Kopecký 1978), features that were beyond the focus of this study. The arrangement of the seven major vegetation types followed a general pattern in zones parallel to the roadway. Each type has indicator species with varying degrees of overlap between types. The zonation of these physiognomic vegetation types (VT I–VII) from the roadside inwards can be characterized according to the landform unit on which it occurred as follows:

  • (a) Coastal plain ; at the inner edge of the road verge and exposed to salt spray. Vegetation composition in this landform was dominated with Ammophila arenaria–Pancratium maritimum (VT IV) found very close to the seashore on the low-lying stands rich in fine sediments . Less frequent species include Elymus farctus and Silene succulenta .

  • (b) Saline depressions ; located on the outermost zone of the outer road verge that were relatively influenced by seawater and forming wet salt marshes . They dominated with Zygophyllum album, Arthrocnemum macrostachyum, and Arthrocnemum macrostachyum–Zygophyllum album (VT V, VI, and VII, respectively). High salinity of this landform favours the growth of some salt-tolerant species as Frankenia hirsuta, Juncus rigidus, Agathophora alopecuroides, and Cyperus laevigatus. Low species richness in the vegetation types of the coastal plain and saline depressions may be related to their high soil salinity. Our results indicated that species richness was negatively correlated with soil salinity and positively correlated with landform units. Such salinity stress on species diversity in the study area and related areas was reported (Moustafa and Klopatek 1995; Shaltout et al. 1997) .

  • (c) Sand plains : followed the saline depressions and away from the direct influence of the sea. The vegetation structure of this vegetation type occurred in two facies: (1) the farthest from the seashore and inhabiting the deep sandy soil stands with low content of CaCO₃. It is dominated with Panicum turgidum and Thymelaea hirsuta (2), the nearest to the seashore found on high soil contents of CaCO₃, pH, and fine sediments . It represents the typical vegetation type that dominated with Artemisia monosperma–Echinops spinosus (VT II). The relatively high species diversity of VT (II) may be explained in terms of the theory of substrate heterogeneity (Mellinger and McNaughton 1975), as this landform can be considered as ecotonal area that embraces the characteristics of both coastal plain and sand dunes . High species diversity due to substrate heterogeneity and local topographic variations in some Mediterranean plant communities was also confirmed (among others Kutiel et al. 1979, Behhouhou et al. 2001, Al-Sodany et al. 2003) .

  • (d) Sand dunes : represents the innermost zone of the outer road verge away from any influence of the sea and characterized with Artemisia monosperma (VT I), Artemisia monosperma–Echinops spinosus (VT II), and Cyperus capitatus–Ammophila arenaria (VT III). The vegetation composition of the coastal sand dunes in the present study has very much in common with those in Israel (Barbour et al. 1981; Tielbörger 1997) and in the western Mediterranean coast of Egypt (Ayyad 1973). The coastal sand dune system was a prominent feature in this study. However, its vegetation has been disturbed through grazing and over-exploitation for fuelwood, construction, and being burnt to clear the way for cultivation. Consequently, the high species diversity and the highest share of alien weeds of vegetation types (I) and (III) characterized sand dune vegetation in the study area may be related to the high disturbance of their substrates as a result of agriculture practising, farming processes, and other excessive human disturbances .

8.1 A Coastal Plain in South Sinai (El-Qaa Plain)

El-Qaa plain (33° 20′–34° 10′E and 27° 47′ – 28° 41′N) occupies the southwestern corner of Sinai Peninsula (Zahran and Willis 2009). It is a depression of about 1,125 km², extending for about 100 km along the southern section of the eastern coast of the Gulf of Suez (Fig. 3.16). To the east, it is bounded by the outskirts of the rugged montane area of south Sinai and to the north by wadi Feiran. The plain rises up to 200 m above sea level (ASL) , sloping gently towards the south east of the Peninsula. It is characterized by young tertiary and quaternary alluvial sediments, sandstone, gypsum, and limestone. Much of the alluvial sediments originate from the hills to the east. Alluvial fans derived from magmatic and metamorphic parent rocks are common in the southern part of Sinai Massif. Limestone derived from local weathering and transported by wind mixes with the alluvium or forms individual dunes (Danin 1983). The plain is divided into six geomorphologic units : terraces , alluvial plains , wadi channels, alluvial fans , playas , and coastal shore . The climate of El-Qaa plain does not differ greatly from that of southern Sinai, which is hot, with low rainfall and high relative humidity . Ayyad et al. (1983) considered the area to be one of the driest parts of Egypt. It belongs to the hyperarid bioclimatic province with precipitation less than 30 mm year⁻¹. Comparing climatic characteristics of three meteorological stations in Sinai Peninsula , El-Tor station, the nearest to El-Qaa plain, with the other two is shown in Table 3.14. Obviously, a rainfall gradient along the N–S direction (from El-Arish in the north to El-Tor in the south) can be detected.

Fig. 3.16

Location map of El-Qaa plain showing the distribution of the studied sites (1–19) within the six geomorphologic units . A, b, and c are three climatic stations at El-Arish, Suez, and El-Tor, respectively

Table 3.14 Climatic characteristics (average 1975–1985; Meteorological authority 1989) of three stations: El-Tor (within the study area), Suez to the north, and El-Arish (on the Mediterranean coast) for comparison

Zahran and Willis (2009) reported that scanty rainfall on the mountains is one of the main water resources in southern Sinai, which runs over the slopes and collects in narrow deep wadis forming perpetual streams and rivulets. In rainy years, the excess water percolates and is stored in rock crevices. It may be obtained by digging wells within an average water table ranging between 17–25 m in old wells and 35–40 m in the new ones. Since permanent watercourses are devoid, cultivation therefore depends on groundwater supplies that are extracted by motor-driven pumps. Agriculture is mainly practised in the middle sector of El-Qaa plain near El-Tor City on the Red Sea coast, where parts of the plain are recently cultivated. Among the main cultivated plants are wheat (Triticum aestivum), alfa-alfa (Medicago sativa), maize (Zea mays), date palm (Phoenix dactylifera), and various vegetables. The lack of good drainage system has resulted in the salinization of several cultivated parts of the plain.

9 Floristic Relations

In total, 203 species representing 129 genera and 29 families are collected and identified in this study. Grasses constitute only 9% of the recorded species, while the woody perennials (shrubs and subshrubs) are highly dominated (46%). The largest families are Asteraceae (n = 24), Fabaceae (n = 23), Chenopodiaceae (n = 19), Poaceae (n = 18), and Zygophyllaceae (n = 11), representing 12%, 11%, 9%, 8%, and 5% of the total flora, respectively. The best represented genera are Astragalus (7), Fagonia (6), Stipagrostis (5), Atriplex, Lotus, Plantago, and Zygophyllum (4 for each).

None of the 203 species occurs at all the 19 sites. Some of the recorded species have a wide ecological and sociological range of distribution, e.g. Deverra tortuosa and Zygophyllum coccineum, with ten records and the highest species occurrence (P = 53%), while Zygophyllum simplex recorded in seven sites and showed the highest occurrence among annuals (P = 37%). One hundred fifty-six species or 77% of the total recorded species demonstrated a certain degree of fidelity , where they exclusively recorded in or confined to a certain geomorphologic unit and do not penetrate elsewhere. These species are distributed as follows: 20 in the terraces (e.g. Stachys aegyptiaca, Varthemia montana, Otostegia fruticosa, and Launaea spinosa), 47 in the alluvial plains (e.g. Anabasis setifera, Echiochilon fruticosum, Asteriscus graveolens, Traganum nudatum, Limonium axillare, and Salsola schweinfurthii), 62 in the wadi channels (e.g. Pulicaria arabica, Teucrium leucocladum, Cleome droserifolia, Gymnocarpos decanter, Salvia aegyptiaca, Blepharis ciliaris, and Haplophyllum tuberculatum), 7 in the alluvial fans (e.g. Astragalus camelorum, Launaea tenuiloba, and Pulicaria crispa), and 20 in the coastal shore and playas (e.g. Haloxylon salicornicum, Salsola tetrandra, Haloxylon persicum, Juncus rigidus, and Suaeda vermiculata). Floristic composition in the different geomorphologic landscape units showed differences in species richness. The highest mean species richness of 19.7 ± 1.7 is recorded in the wadi channels, whereas the lowest species richness values are recorded in the coastal shore and playas (6.0 ± 1.4) and in the alluvial fans (mean of 8.4 ± 1.6 species). Terraces and alluvial plains demonstrated intermediate species richness value of 14.8 ± 2.5 and 14.3 ± 1.5, respectively . Therophytes are the predominant life form and constituted 50% of the total flora, followed by chamaephytes (26%), hemicryptophytes (21%), and phanerophytes (18%). Apart from the playas and the coastal shore , preponderance of therophytes upon the other life forms in the geomorphologic units is remarkable (Fig. 3.17).

Fig. 3.17

Life-form spectrum within each geomorphologic unit of El-Qaa plain. Ph phanerophytes, CH chamaephytes , Hc hemicryptophytes, G geophytes, He helophytes, and Th therophytes

Results of the total chorological analysis of the surveyed flora presented in Table 3.15 revealed that 46% of the studied species are uniregional, of which 41% being native to the Saharo–Arabian chorotype. Typical Mediterranean and Sudano–Zambezian chorotypes are very modestly represented. About 50% of the recorded species are biregional and pluriregional, extending their distribution all over the Saharo–Arabian, Sudano–Zambezian, Irano–Turanian , and Mediterranean chorotypes . The biregional Saharo–Arabian and Mediterranean, the Saharo–Arabian and Irano–Turanian, and the Saharo–Arabian and Sudano–Zambezian chorotypes constituted the highest values (13%, 12%, and 11%, respectively), while Cosmopolitan and endemic taxa rarely occurred.

Table 3.15 Chorotype analysis of the species examined as numbers and percentages of the total species recorded

9.1 Classification of the Vegetation

The TWINSPAN classification of the 19 sites resulted in five site groups (A–E, Table 3.16, Fig. 3.18), each of which could easily be linked to a geomorphologic unit presented in Fig. 17. Each site group will be referred here to as TWINSPAN vegetation group and named after the leading dominant species that exerts local dominance or is distinctly important in a certain group of sites. Sørensen’s coefficients of floristic similarity (CCs) between the five vegetation groups are generally low (Table 3.17). Among the significant relations are those between groups A, B, and C and between groups B and E. However, groups D and E have the lowest similarities with other groups.

Table 3.16 Synoptic table of the indicator and preferential species of the five TWINSPAN groups (A–E) with their presence estimates

Fig. 3.18

TWINSPAN classification of the 19 sites of EL-Qaa plain. A–E are the five separated vegetation groups

Table 3.17 Sørensen’s coefficient of floristic similarity (CCs) between the TWINSPAN vegetation groups

Group A. Capparis spinosa var. spinosa Group

The four plots in this group are sampled from one site (15) that was accessible to us. On highly saline, gravel, and fertile soils with the lowest amount of calcium carbonate (Table 3.18), terraces of Capparis spinosa var. spinosa are found. Apart from Calotropis procera, shrubs and subshrubs of Gomphocarpus sinaicus, Varthemea montana, Launaea spinosa, Stachys aegyptiaca, Echinops glaberrimus, and Deverra triradiata are also recorded. The herb layer is relatively sparse and characterized by Euphorbia granulata, Hyparrhenia hirta, Andrachne hispida, Stipa capensis, Anchusa hispida, and Plantago afra .

Table 3.18 Mean values , standard deviation errors, and ANOVA F-values of the soil variables in the sites representing the five vegetation groups obtained by TWINSPAN

Group B. Cornulaca monacantha–Convolvulus lanatus Group

This group is characterized by a combination of Cornulaca monacantha and Convolvulus lanatus found on the alluvial plains , somewhat fertile, with high soil content of sand and gypsum. It is differentiated by a number of woody species (Artemisia monosperma, Halogeton alopecuroides, Salsola schweinfurthii, Anabasis setifera, Farsetia aegyptiaca, Zygophyllum dumosum, Deverra tortuosa, Heliotropium arbainense, and Acacia tortilis subsp. tortilis) and herbs (Trigonella stellata, Rumex vesicarius, Diplotaxis acris, Lotus glinoides, and Morettia parviflora). This vegetation group includes the most common xerophytic species in the Egyptian Deserts, Sinai, and in the neighbouring arid environments as well (Zohary 1973; Batanouny 1979a; Abd El-Ghani 1998). It is noteworthy that due to the relatively high soil salinity, some salt-tolerant and moist-loving species are recorded and include Halopeplis perfoliata, Spergularia diandra, Limonium axillare, Limoniastrum pruinosum, and Atriplex dimorphestegia. Since the alluvial plains form the main geomorphologic landscape unit in El-Qaa plain, this vegetation group includes the most widespread species in the study area .

Group C. Cotula cinerea–Filago desertorum–Launaea nudicaulis Group

This is the largest group of sample plots (30) and the most diversified among the other vegetation groups. It inhabits the wadi channels on the alkaline soils (pH=8.4) with the lowest levels of soil salinity, gypsum, and organic matter. Ziziphus spina-christi is the only tree species recorded, whereas Cassia italica, Iphiona scabra, Hyoscyamus muticus, Pulicaria arabica, Convolvulus hystrix, and Artemisia judaica constitute the shrub and subshrub layer. This group had the largest share (46) of annual species. Shortly after rainfall, the soil surface supporting the sites of this group is covered with a dense vegetation of annual species, especially Trigonella stellata, Oligomeris linifolia, Parietaria alsinifolia, Sonchus oleraceus, Silene villosa, Aristida adscensionis, Plantago ciliata, Schismus arabicus, Medicago laciniata, and Matthiola livida .

Group D. Acacia tortilis subsp. raddiana–Leptadenia pyrotechnica Group

This group dominates the highly elevated alluvial fans with comparable physical soil properties to those of group C. The nine sample plots studied in this group are characterized by the growth of Acacia tortilis subsp. raddiana and Leptadenia pyrotechnica. In addition, Ziziphus spina-christi, Tamarix nilotica, Tamarix aphylla, and Phoenix dactylifera are occasionally recorded. The shrub and subshrub layer comprise Ficus pseudo-sycomorus, Launaea tenuiloba, Pulicaria crispa, and Deverra tortuosa. The lowest number of annuals is recorded in this group, of which Astragalus camelorum, Anastatica hierochuntica, Ifloga spicata, Zygophyllum simplex, and Filago desertorum are occurred .

Group E. Nitraria retusa–Tamarix nilotica–Zygophyllum album Group

On muddy fertile sites with high calcium carbonate and saline soils, the coastal shore and playas with vegetation characterized by the complex Nitraria retusa, Tamarix nilotica, and Zygophyllum album are found, indicating the saline nature of this geomorphologic landscape unit. It represents the least diversified among the other recognized groups. Notably, several halophytic species are recorded, e.g. Suaeda monoica, Halocnemum strobilaceum, Haloxylon persicum, Atriplex halimus, and Reaumuria negavensis. The herb layer is modestly represented and includes Frankenia pulverulenta, Cressa cretica, Spergularia marina, and Lotus peregrinus, among others .

10 Soil Characteristics of the Vegetation Groups

Soil characteristics of each of the five vegetation groups are summarized in Table 3.18. Of the measured soil parameters, pH, calcium carbonate, gravel, fine soil fraction, and soil saturation show highly significant differences between groups. It can be also noted that soil saturation and calcium carbonate attain their highest levels in the group of playas and coastal shore , the electric conductivity, and gypsum on the terraces and on the alluvial plains .

11 Ordination of Stands

Figure 3.19 shows the ordination results of the DCA analysis of the floristic data set. The 19 site scores are plotted along axes 1 and 2 and tend to cluster into five groups that resulted from TWINSPAN analysis described above. The sites are spread out 7.34 SD units along the first axis (eigenvalue = 0.82), expressing the high floristic variation among vegetation groups and indicating a complete turnover in species composition that took place (Hill 1979). The ordination diagram displays graphically that site groups C and D are transitional in their composition between the other groups. Sites of group E are separated towards the positive end of DCA axis 1, while those of groups A and B are separated out along the other end. DCA axis 2 with an eigenvalue of 0.65 and a gradient length of 5.46 is less important. The species–environment correlation is also high: 0.93 and 0.84 for DCA axes 1 and 2 showing that the species data are strongly related to the measured environmental variables. Significant correlations of soil variables with the first three DCA axes revealed greater correlations along axis 1 than the higher-order axes. DCA axis 1 showed significant positive correlations with CaCO₃, pH, soil saturation, and organic matter (Table 3.18). We interpreted DCA axis 1 as a calcium carbonate–soil saturation gradient. Axis 2 is significantly correlated with pH, electric conductivity, and gypsum. We interpreted axis 2 as an electric conductivity–gypsum gradient .

Fig. 3.19

The floristic DCA ordination of the 19 sites with the TWINSPAN groups superimposed

12 Vegetation and Soil Factors

The eigenvalues (Table 3.19) are somewhat lower than for the DCA axes, indicating that important explanatory site variables are not measured and included in the analysis or some of the variation is not explained by environmental variables (Franklin and Merlin 1992; McDonald et al. 1996). However, the species–environment correlations are higher for the first three canonical axes, explaining 67% of the cumulative variance. These results suggest a strong association between vegetation and the measured soil parameters presented in the biplot (Jongman et al. 1987). From the intra-set correlations of the soil factors with the first three axes of CCA, it can be noted that CCA axis 1 is correlated to soil reaction, calcium carbonate, organic matter, and soil saturation (Fig. 3.20). A test for significance with an unrestricted Monte Carlo permutation test (99 permutations) found the F-ratio for the eigenvalue of axis 1 and the trace statistics to be significant (P < 0.001), indicating that observed patterns did not arise by chance. It is worthwhile to note that the results of DCA demonstrated patterns very similar to those of CCA, suggesting that there might be no other important environmental variables missed in sampling. CCA axis 2 is clearly related to pH, gypsum, organic matter, soil salinity, and gravel. As a result of the significant differences between groups in relation to certain soil factors, their species and space have been arranged along axes 1 and 2 of the CCA scatter diagram .

Table 3.19 Comparison of the results of ordination for the first three axes of DCA and CCA . Intra-set correlations of the soil variables , together with eigenvalues and species–environment correlation coefficients

Fig. 3.20

CCA ordination biplot of the first two axes showing the distribution of the 19 sites with their TWINSPAN groups (A–E) and the examined soil variables

13 Concluding Remarks

• 1. The present study examined the environmental correlates of species distribution in different geomorphologic units of El-Qaa plain along the southwestern coast of the Gulf of Suez, southern Sinai. Both DCA and CCA assess the soil–vegetation relationships. The results of CCA analysis showed well the relative positions of species and sites along the most important ecological gradients. Both ordination techniques clearly indicated that soil surface sediments, calcium carbonate, soil reaction, organic matter, and soil saturation percentage are the most important factors for the distribution of the vegetation pattern in El-Qaa plain. The soil texture gradient that exists from the upland terraces to fine-textured flats in the alluvial plains and wadi channels in arid desert environments resulted in gradients of available soil moisture. The organic matter content plays an important role as a key element in soil fertility, as shown for other desert ecosystems in Egypt by Sharaf El Din and Shaltout (1985) and Abd El-Ghani (1998, 2000b) and in Saudi Arabia by El-Demerdash et al. (1994).

• 2. The plant life in the study area is restricted to microenvironments (as in wadis, runnels, and depressions) where runoff water collects and provides sufficient moisture for plant growth. This is described by Monod (1954) as végétation contracté, runoff desert (Zohary 1962), and restricted desert (Walter 1963). The vegetation is characterized by sparseness of plant cover (does not exceed 5% on the average; Kassas 1966), a limited number of plant species (16 on the average in each site), and paucity of trees (5% of the recorded species). The vegetation structure is relatively simple, in which the species have to withstand the harsh environmental conditions . This is not only reflected by the preponderance of annuals but also by the presence of several highly adapted, drought-resistant species (Abdel-Razik et al. 1984). Monodominant plots in the study area are not as common as those dominated by more than one species. Monotypic stands dominated by Artemisia judaica are recorded in wadi El-Sheikh of south Sinai (El-Ghareeb and Shabana 1990), whereas in gorges of Gebel Uweinat and in Gilf Kebir (SW corner of Egypt) are dominated by Cornulaca monacantha and Zygophyllum coccineum (Boulos 1982; Bornkamm 1986).

• 3. The importance of the study area from a phytogeographical point of view may be due to its position on the Sinai Peninsula , which is located in the intersection of the four phytogeographic regions: Mediterranean, Irano–Turanian , Sudano–Zambezian , and the Saharo–Arabian region. This may reflect the relatively rich floristic diversity of the Sinai Peninsula. Chorological analysis of the floristic data revealed that the Saharo–Arabian chorotype (46%) forms the major component of the floristic structure along El-Qaa plain. This is in accordance with the results obtained by Danin and Plitman (1987) on the phytogeographical analysis of the flora of Israel and Sinai. The presence of the monoregional Saharo–Arabian chorotype in a higher percentage than the interregional chorotypes (bi- and pluriregionals) is not in accordance with Zohary (1973). The Saharo–Arabian chorotype decreased northwards and replaced by Mediterranean and Irano–Turanian chorotype (Hegazy and Amer 2001; Danin and Plitman 1987). This may be attributed to the fact that plants of the Saharo–Arabian species are good indicators for desert environmental conditions, while Mediterranean species stand for more mesic environment. The low percentage of the endemic species is remarkable. Wickens (1977) and Boulos (1997) mentioned that the Saharo–Arabian region is characterized by the presence of few endemic species and genera and absence of endemic families. Most of the endemic species in Sinai is confined to the mountain region (El Hadidi 1967).

• 4. Spatial distribution of plant species and communities over a small geographic area in desert ecosystems is related to heterogeneous topography and landform pattern (Kassas and Batanouny 1984). The heterogeneity of local topography, edaphic factors, and microclimatic conditions leads to variation of the distributional behaviour of the plant associations of the study area. In terms of classification, the vegetation that characterizes the study area can be divided into five vegetation groups. Most of the identified vegetation groups have very much in common with that recorded in some wadis of the Eastern Desert (Kassas and Zahran 1965; Abd El-Ghani 1998), Western Desert (Bornkamm and Kehl 1990; Abd El-Ghani 2000a, b), along the eastern (El-Demerdash et al. 1994) and western Mediterranean region (Ayyad and El-Ghareeb 1982), in south Sinai region (El-Ghareeb and Shabana 1990; Moustafa and Zaghloul 1996; El-Kady et al. 1998), and in northwestern Negev, Israel (Tielbörger 1997). The members of each pair of groups are, in some cases, linked together by having one of the dominant species in common. Group E comprises a number of salt-tolerant species , e.g. Tamarix nilotica, Zygophyllum album, and Nitraria retusa, occupying the playas and the coastal shores . According to Kassas and Girgis (1965), the growth of the desert scrub Nitraria retusa represents the highest tolerance to soil salinity conditions and a penultimate stage in the successional development . The plant reaches its northernmost limit of distribution around Qara Oasis on the southwestern edge of Qattara Depression (Abd El-Ghani 1992) as well as in Bahariya Oasis (Abd El-Ghani 1981). Suaeda monoica is among the tropical species which extends northwards to south Sinai. It grows in a pure community or mixed with Nitraria retusa forming sand hillocks in littoral and inland salinized parts in the studied area. The presence of Suaeda monoica in El-Qaa plain forms a tropical corridor that represents the extreme northern limit of the species distribution in Egypt (Hegazy and Amer 2001). Further studies on the biogeography and conservation biology of the aforementioned plants in the country are strongly recommended. Group A includes Capparis spinosa var. spinosa that occupied the terraces . Since the alluvial plains form the main geomorphologic landscape unit in El-Qaa plain, group B includes the most widespread species in the study area. It is dominated by the xero-psammophytes Cornulaca monacantha, Convolvulus lanatus, and Deverra tortuosa, inhabited the alluvial dry nonsaline plains where infiltration is higher and water accumulated in deeper layers. This group of species is more widely distributed in Egypt and neighbouring countries (Batanouny 1979b; Zahran and Willis 1992; Frankenburg and Klaus 1980). Calculation of Søensen’s coefficient of floristic similarity (CC) between the TWINSPAN groups indicates significant differences of the species compositional changes between the wadi channels and both the terraces and the alluvial plains . This may be related to the comparable soil characters of these landforms.

• 5. Under the conditions of low and irregular rainfall which prevail in the study area, local topography is one of the overriding factors controlling sedimentation and water redistribution within the local landscape (Zohary 1962). Therefore, topographic variations usually translate into high habitat heterogeneity and corresponding species diversity (Kassas and El-Abyad 1962). In extreme conditions notably high aridity and high salinity, Danin (1976) summarized that low diversities of vascular plants are expected in extreme deserts, high Arctic and high alpine habitats, salt marshes , and mangrove swamps. The present study reveals that the lowland wadi channels (group C) that receive considerable amounts of runoff water have the highest species richness (19.7 species ±1.7). The agricultural processes practised in this area may also contribute to the high share of annuals recorded . The highly salinized soil with deep fine sediments (group E) dominated by Tamarix nilotica, Zygophyllum album, and Nitraria retusa have the lowest species richness (6.0 species ±1.6).

Photo Gallery

Photo 3.1

Euphorbia dendroides growing on Sallum Pateaux along the Egyptian–Libyan borders

Photo 3.2

The limestone plateaux along the Mediterranean western coastal desert showing sparse vegetation

Photo 3.3

Shrubs of Thymelaea hirsuta dominating the desert vegetation in Sallum area

Photo 3.4

Cistanche phelypaea ; a desert parasite in the Sallum area

Photo 3.5

Vigor growth of Chrysanthemum coronarium growing in the limestone plateaux of the Sallum area

Photo 3.6

Inland desert vegetation of Haloxylon salicornicum in the Sallum area. Note the coastal sand dunes in the background