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Contents Title Introduction and Aim of the Work Review of Literature The Study Area Material and Methods Results Discussion Summary References Appendices
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Page 2 6 22 43 58 127 131 133 146
Introduction The Western Desert of Egypt occurs on the west side of the River Nile. It extends from the Mediterranean coast in the north to the Egyptian– Sudanian border in the south (about 1073 km), and from the Nile Valley in the east to the Egyptian–Libyan border in the west, a width between 600 and 750 km. It covers about 689.000 km2 that represents approximately two–third of Egypt`s area. In general, the interior plateau of the Western Desert is flat; there is nothing but plains or rocks, either bare or covered with sand and detrital material, broken abruptly by any conspicuous relief feature. It thus appears as a large rocky plateau of moderate altitude (mean elevation = 500 m above sea level). Except for the narrow Mediterranean coastal belt, which is the wettest region of Egypt, the whole Western Desert is one of the extremely arid parts of the world. It’s very great aridity results from its distant position from Sea, coupled with the absence of high altitudes, which may receive orographic rain (Zahran & Willis, 1992). Another salient feature, resulting from arid conditions is the uniformity of the surface compared with other parts of North Africa. The plant cover in this vast area is mainly confined to the Mediterranean coastal land and the Oases. The desert vegetation is by far the most important and characteristic type of natural plant life. It covers extensive areas and is formed mainly of xerophytic shrubs and subshrubs. Monod (1954) recognized two types of desert vegetation namely contracted and diffuse. Both types refer to permanent vegetation that can be accompanied by ephemeral (or annual) plant growth depending on the amount of precipitation in a given year. In a survey of the vegetation units in the Western Desert, outside the Oases, Bornkamm & Kehl (1990) distinguished five desert zones along a precipitation gradient. Besides the well-known semi-desert and full desert zones in the north, three zones of extreme desert show significant differentiation. On a phytogeographic basis, El Hadidi (2000) divided the Western Desert of Egypt into three main teritories: The northern part of inland Desert where Siwa, Bahariya and north Farafra Oases are situated and 2
known as Libyan Desert. The southren part where south Farafra, Dakhla, Kharga and Gebel Uweinat are situated and known as the Nubian Desert. The northren strip of the desert adjacent to the Mediterranean Sea and known as the Mareotis sector of the Mediterranean coastal land extending between Egypt-Libyan borders, eastward to Rosetta. Unlike the Eastren Desert, the Westren Desert is floristically richer and includes about 50% of the Egyptian flora. The main bulk of this flora is mainly found along the westren Mediterranean coastal land. Of the 61 endemic taxa enumerated by Boulos (1995), 4 species are endemic to the Mediterranean region and 5 species endemic to the Mediterranean and other regions in Egypt. In addition, El Hadidi et al. (1992) paid the attention to the occurrence of 24 threatened plant species in the whole Desert. According to El Hadidi (2000), the Westren Desert consists of six geomorphologic subdivisions, (1) the Mediterranean Coastal Plain, (2) the Northern Plateau, (3) the Southern Plateau, (4) the Great Sand Sea, (5) the Depressions and (6) the Mountainous area (Map 1). The Mediterranean Coastal Plain extends from Sallum eastward to Rafah for about 970 km, and is divided ecologically into three sections (Map 1), (a) westren, extends from Sallum to Abo-Qir; (b) middle, runs from Abo-Qir to Port Said; and (c) eastren, stretches from Port Said to Rafah (Zahran et al., 1985,1990). Physiographically, the westren section is distinguished into two main provinces: an Eastren Province between Alexandria and Ras ElHekma, and a Westren Province between Ras El-Hekma and Sallum (Hammouda, 1982) Map (2). Despite the wealth of studies that have been conducted in the eastern and middle sectors of the Mediterranean coastal land, little attention has been paid to the distant part of the western sector from Sidi Barrani to Sallum. This part will be referred to as Sallum area throughout this work. Apart from Zaki (1968) who studied the ecology and phytosociology of Abu Nafla sector in Sidi Barrani, the least is known about the floristic composition and the vegetation structure in the Sallum area.
3
Map (1): The main geomorphologic units of Egypt, partially after Millington (1993).
Therefore, the present study has been carried out to answer the following key questions: (1) what are the present status of the floristic composition of the vegetation in this area? (2) What are the main phytochoria, which constitute the main bulk of the recorded flora, and consequently the phytochorological affinities between them? (3) What are the major environmental gradients associated with the observed patterns of plant communities? (4) Is the distribution of plant communities adequately explained by the environmental variables considered or are other factors more important in determining species distribution? (5) What are the factors affecting the diversity of plant communities inhabiting the study area? . It is hoped that an updated floristic list and distribution maps for the perennial species of the Sallum area will be prepared.
4
5
Map (2): Location map of the western Mediterranean coastal land of Egypt, after Hammuda (1982)
Review of Literature In ecological studies of certain habitats of the Mediterranean coastal region of Egypt; variations in the distribution of vegetation type have been recognized in association with edaphic and topographic variations in various habitats. These studies were either extensive general survey, or intensive with the objective of correlating vegetational and environmental variables, all were dealing with specific types of habitat or confined to limited locations. The local distribution of communities in different habitats is linked primarily to physiographic variations. Ayyad (1973) reported that according to these variations two main sets of habitats might be distinguished in the western Mediterranean region of Egypt, one on ridges and plateaus, and the other in depressions. Ridge and plateau habitats may be further differentiated into two main types: (1) the coastal ridge is composed mainly of snow-white oolitic calcareous grains overlained by dunes in most of its parts, and the inland less calcareous ridges, and (2) the southern tableland. According to Ayyad (1973), seven main habitats may be recognized along the western Mediterranean coast: (1) coastal calcareous dunes, (2) inland siliceous deposits, (3) ridges, (4) inland plateau, (5) wadis, (6) saline and marshy depressions, (7) non-saline depressions. Each of these habitats is characterized by local variation in physiography, which result in the formation of a mosaic of micro sites with local variation in vegetation composition. El Hadidi (2000) suggested the occurrence of 8 habitats in the western Mediterranean coastal land: (1) rocky ridges, (2) inland siliceous depressions, (3) wadis (gullies), (4) littoral salt marshes, (5) coastal dunes, (6) calcareous duns at Abu Sir, (7) siliceous dunes at Abu Mandur, (8) farmland vegetation. According to Emberger’s classification system, the vegetation of the western Mediterranean coast of Egypt belongs to the groups existing under the maritime type of the Mediterranean climate (Emberger, 1971). Communities of this vegetation may not have closely similar composition to those of adjacent countries but dominant and characteristic species are often the same. Several authors; e.g. Eig (1938,1939,1946), Boyko (1949), Zohary & Feinbrun (1951), and Danin et al., (1964) in Palestine, and Brau-Blanquet (1949), Long (1949,1950,1952), LeHouerou (1969), in 6
North Africa, recognized communities dominated by Thymelaea hirsuta, Artemisia herba-alba, Asphodelus tenuifolius, Anabasis articulata, Thymus capitatus, Achillea santolina, Gymnocarpos decander, Suaeda monoica, Atriplex halimus and others. These species are also very common in the western Mediterranean coastal region of Egypt. According to geobotanical map of the Middle East (Zohary 1973), the vegetation of the northern section of the western Mediterranean coastal desert of Egypt belongs to the Mediterranean woodland climax, and that of the southern section to the Saharo-Arabian desert vegetation. It may be considered to consist of a skeleton of perennial plant life that is confined to sepecially favoured habitats and ephemeral waves of short-lived plant growth that may outflow the limits of dynamic rhythm of plant life varies in magnitude as one passes from the extremely arid (rainless) Sahara to the Mediterranean steppe to the north or the tropical steppe to the south (Kassas, 1970). Tag El-Din (1969) recognized eight plant associations representing the major vegetation types in the northwestern Mediterranean coastal land. These were: 1- The association of Salsola tetrandra - Suaeda vermiculata, occupies the saline area. 2- The association of Artemisia herba-alba - Asphodelus tenuifolius, 3- The assocation of Thymelaea hirsuta, 4- The association of Thymelaea hirsuta - Gymnocarpos decander, occupies the original desert soil. 5- The association of Haloxylon scoparium – Anabasis articulata, occupies the degraded soil. 6- The association of Plantago albicans- Echiochilon fruticosum, 7- The association of Urginea maritima. occupies the inland dunes. 8- The ecotone between the association of Artemisia herba-alba and Asphodelus tenuifolius, and the association of Haloxylon scoparium and Anabasis articulata. El-Ghonemy & Tadros (1970) recognized the vegetation of the northern section of the western Mediterranean coastal as belonging to the Thmelaeion hirsute alliance with two associations as: (1) Thymelaea hirsuta –Noaea mucronata association with two variants a wet variant dominated by Asphodelus tenuifolius and dry variant dominated by 7
Achillea santolina, (2) Anabasis articulata, Suaeda pruinosa association. The vegetation of the southern section may refered to the lithospermetum association with Linum strictum, Polycarpaea repens, Artemisia monosperma, and Convolvulus lanatus as the most faithful characteristic species. Hammouda (1982) reported that the most common perennials in the vegetation of the western Mediterranean coastal land were Thyemelaea hirsuta, Deverra tortuosa, Anabasis articulata, Gymnocarpos decander, and Salvia lanigera, and the most rare were Stipagrostis ciliata, Diplotaxis simplex, Heliotropium bacciferum, Polycarpaea repens, Sonchus oleraceaus, Atriplex semibaccata, Anchusa milleri and Polycarpon succulentum. Some species exhibited wide amplitudes of tolerance, being recorded in all habitats such as: Thymelaea hirsuta, Plantago albicans, Gymnocarpos decander, Cutandia dichotoma and Anacyclus alexandrinus, while some others had narrow amplitude of tolerance, being recorded in only one habitat. Chasmophytic species, which were more or less strictly associated with rocky substrates, were: Thymus capitatus, Globularia arabica and Dactylis glomerata. Species, which were highly associated with the most saline soils, were Halocnemum strobilaceum and Arthrocnemum macrostachyum of perennials, and Sphenopus divaricatus of annuals. Species, which were highly associated with location of the most calcareous soils, were Ammophila arenaria, Euphorbia paralias and Lotus polyphyllos. None of the species was highly associated with sites of the least calcareous soils. Most species did not exhibit high degrees of association with variations in clay percentage. Convolvulus lanatus and Euphorbia paralias were highly associated with soils of low percentage of clay. Frankenia revoluta, Halocnemum strobilaceum and Limoniastrum monopetalum were highly associated with soils of high percentage of clay. The following is short review about the vegetation of the different habitat of the western Mediterranean coast of Egypt. 1- Coastal Dunes Next to the sea shore there is a discontinuous belt of sand dunes. These dunes are formed of white coarse, pseudo-ooltic calcareous granular sand. The dunes varying in width from few meters to 2 km. These dunes are more humid and exposed to immediate effect of the northerly winds and 8
usually exposed to sea spray (Ahmed & Mounir, 1982). The dunes vegetation in the western Mediterranean coastal land of Egypt has been briefly described by Montasir (1943), Oliver (1946), Tadros (1956) and Tadros & Atta (1958) who distinguished between communities of young dunes dominated by Ammophila arenaria and Euphorbia paralias, and those of older dunes, dominated by Crucianella maritima and Ononis vaginalis. The analysis of variation in soil characters of the habitat of coastal dunes carried out by Ayyad (1973) and Ayyad & El- Bayyomi (1980) indicated that they are generally do not exhibit clear trends during the process of dune formation. Accordingly, it was concluded that the abundance of species is largely related to the physical processes of dunes stabilization rather than to changes in soil characters. At the initial stage of dune formation it is unstable, and is dominated by Ammophila arenaria. Sand shadows are co-dominated by a group of equally abundant species: Crucianella maritima, Agropyron cristatum, Echinops spinosus, Ononis vaginalis, and Thyemlaea hirsuta. The exposed coastal ridge is codominated by Crucianella maritima and Deverra tourtosa. In more advanced stages of dune stabilization, communities of Euphorbia paralias, Pancratium maritimum, Elymus farctus, Crucianella maritima, Echinops spinosus and Thymelaea hirsuta become successively more and more common. During succesion Louts polyphyllos, Euphorbia paralias, Elymus farctus and Crucianella maritima become more and more abundant until they dominate stable dunes and protected deep sand sheets. Kamal (1982) classified the vegetation of coastal dunes using multivariate techniques in relation to the depth of sand cover, and salinity: a) Ammophila arenaria, Euphorbia paralias and Lotus polyphyllos on active baby dunes near the shore; b) Ammophila arenaria and Pancratium maritimum on protected seaward slopes of active dune; c) Pancratium maritimum, Hyoseris lucida, Silene succulenta, Centaurea pumilio and Echinops spinosus on partly stabilized dunes; d) Elymus farctus, Echinopos spinosus, Crucianella maritima, Ononis vaginalis and Thymelaea hirsuta on stabilized dunes and protected deep sand shadows;
9
e) Launaea tenuiloba, Launaea resedifolia, Echium sericeum and Salvia lanigera on shallow sand shadows; f) Varthemia candicans, Teucrium polium and Deverra tortuosa on the exposed coastal ridge; and g) Cakile maritima, Aleuropus lagopoides, Zygophyllum album and Nitraria retusa in transitional locations between coastal and saline depressions. Abo Sitta (1981) distinguished three main ecogeomorphological units could be distinguished in Mediterranean coastal zone: (1) coastal sand dunes, (2) salines and (3) sandy plains. The distinguished plant communities were: 1) Ammophila arenaria community on the loose calcareous coastal sand dunes. Euphorbia paralias co-dominates this community. In particular parts, a few individuals of other species are recorded, e.g., Agropyrun cristatum, Hyoseris lucida and Lotus polyphyllos. 2) Lycium europaeum community on the consolidatid coastal dunes. Other common perennials include Retama retam and Euphorbia paralias. 3) Halocnemum strobilaceum community in the wet salines .The dominant plant contributes to the major of the plant cover and forms low phytogenic mounds. A few individuals of Arthrocnemum macrostachyum, Limoniastrum monopetalum and Frankenia revoluta occur as weakly presented associates. 4) Limoniastrum monopetalum community in the dry salines, Salsola tetrandra is a common associate. Both species are able to form sizeable phytogenic mounds. 5) Thymelaea hirsuta-Asphodelus tenuifolius community in the sandy plains. The density and growth of these plants differ in different sites according to the soil depth and consequently the water supply. The ephemeral growth is dense in rainy years. However, it fails to appear in dry years. Which are not uncommon, Asphodelus disappears during the dry season. 6) Anabasis articulata community in the sandy plains. The dominant plant forms phytogenic mound of considerable size. The ground surface between the mounds is usually coverd with cobbles and stones and is devoid of plant cover. 10
2- Salt marshes and Saline depressions The saline and marshy habitats are characterized by a shallow water table and/or high level of salinity. Tadros (1953) studied the vegetation of saline and marshy habitats on the western Mediterranean coast of Egypt. Tadros & Atta (1958) extended observations to the shores of lake Mariut and lake Edku and to the margins of the latter. Ayyad (1969) used an ordination technique to demonstrate relative positions of halophilous communities of Ras El-Hikma along unidimensional environmental gradients. Habitats dominated by Lygeum spartum, for instance, were found to occupy low positions on axes of soil pentrability and salinity, while those dominated by Halocnemum strobilaceum attained high positions. Intermediate positions were occupied by habitats of Salsola tetrandra, and Suaeda pruinosa. The sequence of habitat on axes of soil texture and calcium carbonate content were more or less identical on these two axes. The habitats of Suaeda fruticosa attain the lowest positions follwed by those of Salsola tetrandra, Suaeda pruinosa, Halocnemum strobilaceum and Lygaeum spartum. Saline depressions support communities dominated by: Sarcocornia fruticosa, Cressa cretica, Atriplex halimus, Juncus rigidus, Arthrocnemum macrostachyum, and Limonium echioides in sites of high salinity and very shallow water table, Suaeda monoica, Zygophyllum album, Limoniastrum monopetalum, Aeluropus lagopoides, Salsola tetrandra, and Frankenia revoluta in sites with relatively deep water-table but high salinity, Atriplex halimus, Hammada scoparia, and Anabasis articulata in sites with deep water table and relatively low salinity (Long, 1954, Le Houerou, 1959, Novikoff, 1958, 1961, Ayyad & El-Ghareeb, 1972, 1982 ). The associations belonging to these alliances with principal characteristic species, which are also common in the northren coastal area of Egypt, have been described by Braun-Blanquet (1949), LeHouerou (1969) and others in North Africa, and by Zohary (1944, 1947, 1952) in Sinai and Palestine. This may imply that the vegetation of salt marshes of the Mediterrnaen coastal desert of Egypt represents a transition from the westren communities in North Africa and those characteristics of the eastern Mediterranean. ElDemerdash (1984) recorded three groups in the salt marshes of the 11
western Mediterranean coastal region (two dominated by Juncus rigidus, and one by Arthrocnemum macrostachyum), the first groups in most of the study sites are characterized on the average by relatively higher values of total soluble salts (TSS), CaCO3 content, pH, organic carbon and fine particles 3- Plains and non-saline depressions Plains and non-saline depressions furnish the most suitable habitat for plant growth. They are protected from active erosion by wind and receive considerable amounts of downwash soil material and runoff water. Depending on the source of down-wash material and its physical and chemical properties, this habitat supports a wide variety of plant species. The vegetation of non-saline depressions belongs to the PlantaginetoAsphodeletum tenuifolius association (Tadros & Atta 1958). Four communities were recognized, Anabasis articulata community on more or less sandy soils with low contents of CaCO3, Zygophyllum album community where the soil content of CaCO3 and salinity become relatively higher, Plantago albicans community where salinity becomes lower, and Asphodelus tenuifolius-Thymelaea hirsuta community on fine-textured soils (Ayyad 1976 a). Non-saline depressions as well as catchment areas opposite to the wadis provide favourable conditions for cultivation of barley, figs and olives. Farming operations stimulate the growth of a considerable number of species, mostly therophytes. Weeds of barley fields are recognized as Achilleatum santolinae association with subassociations of Chrysanthemum coronariae and Arisaretosum vulgares (Tadros & Atta, 1958). A phytosociological analysis of the non- saline depression by (Ayyad, 1976 b) indicates that Asphodelus tenuifolius and Plantago albicans generally predominate. These are characterized by soil properties which provide to the possible links between the habitat of nonsaline depression and other common habitats in the same region .It is suggested that species distribution in these depressions is largely a product of a long history of human disturbance and it is affected by soil texture and CaCO3 content. Ayyad (1976 b) and Kamal (1982, 1988) recognized the following communities: (a) Anabasis articulata, Echiochilon fruticosum, Helianthemum lippii, Lycium europaeum and Ornithogalum trichophyllum 12
on sandy soils with low content of CaCO3; (b) Zygophllum album, on sandy soils with relatively high content of CaCO3 and salinity; (c) Plantago albicans, on sandy soils of low salinity; (d) Asphodelus tenuifolius and Thymelaea hirsuta on soils of relatively fine texture; and (e) Asphodelus tenuifolius on soils which are intermediate in texture. 4- Rocky ridges The extreme hostility of the habitats of rocky substrates and shallow soils to the vegetation of the Egyptian Desert has been expressed by several ecological studies. Kassas (1952, 1953) and Kassas & Imam (1954) in their studies on the land forms, habitats and plant communities in the Egyptian desert pointed out that rocky substrates provide little possibility for plant growth and that this may further be reduced by exposure and extreme aridity. Habitats with such substrates are inhabited only by plants, which can send their roots into rock crevices. These plants are mainly chasmophytes of genuine affinity to the rocky habitat. The micro-relief may, however, allow for the accumulation of water and soil in notches and depressions. In these, ephemarals may find the possibility to grow during the favorable season. Montasir (1943), gives an account about the life forms of the common species in the rocky habitat at King Mariut and Burg El-Arab areas. Migahid et al. (1955) described the vegetation on the limestone rock at different stages of weathering at the area of Ras El-Hikma. Tadros & Atta (1958) were able to abstract three types of associations in habitats of rock substrates and shallow soils of uncultivated desert areas of Mariut. A Thymelaetum hirsutea was recognized on rocky ridges, a Plantgineto- Asphodeletum tenuifolius on shallow pebbly soils overlying limestone hills, and an Anabasidetum articulatae on gravelly high plateaus which were previously disturbed by cultivation. Important characteristic species of the first association were Thymelaea hirsuta, Gymnocarpos decander, Helianthemum ellipticum, Lotus corniculatus, Herniaria hemistemon, Scorzonera alexandrina, Plantago notata and Stipa capensis. In the second association, the main characteristic species were Plantago albicans, Asphodelus tenuifolius, Linaria haelava, Papaver rhoeas, Centaurea glomerata, Convolvulus althaeoides, Carthamus glaucus and Lolium perenne. The third association 13
is characterized by Anabasis articulata, Haloxylon scoparium, Salsola tetrandra, Suaeda pruinosa and Sarcocornia fruticosa. Transitional communities in binary and tertiary combinations of species were also distinguished. Binary mixtures are Gymnocarpos–Plantago, Plantagosalsola, Plantago-Anabasis and Ononis –Salsosla. Tertiary mixtures are Gymnocarpos–Salsola–Anabasis and Plantago- Salsosla-Anabasis. Migahid & Ayyad (1959) in Ras El-Hikma area distinguished three types of rocky habitat. The first is represented by rocky ridges affected by salt spray from the Sea. These are inhabited by species, which are chasmophytic nature and in the meantime salt tolerant such as Inula crithmoides, Limonium pruinosum and Varthemia candicans. The second type is represented by the inland rocky elevations and is codominated by Thymelaea hirsuta and Gymnocarpos decander. The sites with shallow soils and relicts of human settlements form the third type of rocky habitat. These are occupied by Suaeda pruinosa, Suaeda fruticosa, Gymnocarpos decander, Herniaria hemistemon and Deverra tortuosa as the soil accumulates on slopes, other species may share dominance. On slopes with shallow sandy soil, for instance, Plantago albicans and Asphodelus tenuifolius become common. In their phytosociological study of Maktala sector of Sidi Barrani Migahid et al. (1963) showed that, the distribution of the association depends on elevation, salinity, and soil depth and soil penetrability. Elevation factor may be most important in controlling the distribution of the communities. Its effect is both direct and indirect. Rocky ridges and elevated areas represent a type of habitat, which is unfavorable to plant growth in general for several reasons. In a sector of the Mediterranean coastal region at Abu Nafla west of Mersa Matruh, Zaki (1968) distinguished six vegetation groups: Sasloletum tetrandrae association, Anabasidetum articulatae association, Artemesitum herbaalba association, Association of Plantago albicans and Echiochilon fruticosum, Association of Gymnocarpos decander, sand dune communities (Ammophila arenaria, Ononis vaginalis, Atriplex coriacea). Ayyad (1969) ordinates different types of habitats at Ras El-Hikma area along unidimensional gradients of several edaphic factors. Inland rocky habitats were found to occupy very low positions on the axis of soluble salts, medium positions on the axes of CaCO3, water-holding capacity, and 14
pH, and high positions on the axis of texture. As compared to the inland rocky habitats, the maritime rocky habitats occupy high positions on the axes of soluble salts, texture and CaCO3, a lower position on the axis of water-holding capacity, and a similar position on the pH axis. Ayyad & Ammar (1974) indicates that the vegetation of the inland ridges in the western Mediterranean coast is codominated by Thymus capitatus, Thymelaea hirsuta and Asphodelus tenuifolius, and that the species of this habitats showed no distinct associations. The sites with the lowest moisture availability are dominated by communities of Thymus capitatus and Globularia arabica, while sites with more or less deep soils and high moisture availability are dominated by communities of Asphodelus tenuifolius, Herniaria hemistemon, Plantago albicans, and Thymelaea hirsuta. In sites of intermediate rockiness and moisture availability, Noaea mucronata, Echinops spinosus, Helianthemum ellipticum, Scorzonera alexandrina and Deverra tortuosa. 5- The Wadis Wadis of the western Mediterranean region of Egypt are shallow. According to Kassas & Girgis (1964). These shallow wadis differ from mature great wadis of the Eastern Desert in several aspects. The later are characterized by wide deep and well-defined channels cutting older limestone formations of the Eocene. In shallow wadis, the main channels are comparatively shallow and narrow. This is presumably due to the fact that these wadis are geologically more recent. Most of the species recorded from different habitats of wadis are Mediterranean species, which do not occur in other parts of Egypt (El Hadidi & Ayyad 1975). These Mediterranean species include perennials; mostly woody shrublets, which form the permanent framework of the vegetation; the rest are annuals, which appear after winter rain. The wadi ecosystem may be distinguished into upper, middle and lower positions of slopes and the wadi beds .The upper position of slopes are usually steep and almost completely devoid of soil cover, they support a typical cliff vegetation dominated by Ephedra aphylla, Umbilicus horizontalis, Periploca aphylla, Phlomis floccosa, Lycium europaeum and Asparagus stipularia. The middle slopes are less steep and covered by a shallow soil with mixed stones; the vegetation is 15
dominated by shrubby species of chasmophytic nature as, Limonium sinuatum, Limonium tubiflorum, Gymnocarpos decander, Artemisia inculata and some grasses as: Hyparrhenia hirta and Stipa capensis. The lower position of slopes are gentle where deep soil accumulates and supports meadow-like vegetation of annual species, the most common are: Picris spriengerana, Astragalus hamosus, Medicago truncatula, Hippocrepis bicontorta, Spergularia fallax, Medicago litoralis. In wadi bed the fine soil material has a little chance to settle down due to high velocity of water stream during the rainy season, it is filled up mainly with large boulders and supports sparse vegetation, which is restricted more or less, to shallow soil accumulations between rock fragments. Common perennials in the wadi bed are Echium sericeum, Salvia lanigera, Euphorbia terracina, Cynara sibthorbiana and Allium erdelii and common annuals were Astragalus boeticus, Pisum sativum, Erodium hirtum and Erodium gruinum. Kamal (1988) indicates that the vegetation on the tops and slopes of the wadi sides is similar to that on inland ridges, but the upper positions of the steep slopes support typical cliff vegetation dominanted by Phlomis fluccosa, and Ephedra alata. In the relatively drier inland wadis a community of Zilla spinosa-Lycium shawii, dominates the upper slopes and a community of Atriplex halimus- Salsola tetrandra dominates the wadi bed. Another community was recognized in the cultivated wadi bed, which is dominated by Convolvulus arvensis with a dense cover of weeds. Kamal & El-Kady (1993) studied the vegetation in wadi Washka and wadi Nethely in the western Mediterranean coastal land west of Mersa Matruh. Four vegetation groups were recognized, (A) Haloxylon scoparium-Plantago albicans, (B) Scorzonera alexandrinaHaloxylon scoparium, (C) Scorzonera alexandrina-Launaea resedifolia, (D) Suaeda pruinosa-Salsola tertrandra in wadi Washka, and five in wadi Nethely (ǿ: Gymnocarpos decander-Helianthemum stipulatum, ǿǿ: Scorzonera alexandrina-Plantago albicans, ǿǿǿ: Arisarum vulgareThymelaea hirsuta, ǿV: Anabasis oropediorum - Scorzonera alexandrina, V: Salsola tetragona-Pancratium maritimum. Two phytosociological groups were recognized in addition to those identified in the previous studies. The first is codominated by Anabasis oropediorum and Scorzonera alexandrina and characterizes the plateau of wadi Nethely and the second 16
is co-dominated by Arisarum vulgare and Thymelaea hirsuta and characterizes the lower position near the cultivated bed of the wadi. Among soil factors affecting the distribution of vegetation groups are moisture content, clay, CaCO3, Ca++ and K+. Heneidy & Bidak (1998) reported in some wadis at Matrouh region, the most wide spread vegetation group was that dominated by Salsola tetrandra, while the least spread one was that dominated by Periploca aphylla. Some perennial species have high presence percentage in most the vegetation groups, (e.g. Atractylis carduus and Helianthemum kahiricum), while some other species were restricted to certain vegetation groups, (e.g. Artemisia herba-alba and Zilla spinosa ). Most of the diversity indices were negatively correlated with some soil variables, but have positive correlation with soil texture, CaCO3, salinity, and some nutrients particularly during summer. During spring Haloxylon scoparium group have the highest species richness of perennials (27.2spp/stand), while Carthamus lanatus have the lowest (19.8 spp/stand). Bromus rubens group have the highest species richness of annuals (22.3 spp/satand), while Centaurea glomerata group have the lowest (15.5 spp/stand). The total cover of perennial species was low in vegetation groups characterized by high species richness. For example, the Carthamus lanatus group has low species richness and total cover, which may be partially due to high grazing pressure. 6- Farmland vegetation The farming operations in the barley fields and orchards of fruit tress in the western Mediterranean coastal land of Egypt has stimulated the apperance of a considerable number of species that form the weed flora of these fields. Most of the species are therophytes that flower mainly in spring and dry up with harvesting the crops in May (Oliver, 1938, 1946). The phytosociology of these weeds in their habitat was studied by Tadros & Atta (1958). They concluded that the weed flora is farily homogeneous and form quite a definte association: Achileatum santolinae mareotcum, with two sub associations: 1) Chrysanthemum coronarium (Chrysanthemetosum), and 2) Arisarum vulgare (Arisaretosum). The study of Kamal (1982) indicated that the therophytic species, which dominate the cultivated fields, occupy one end of the primary ordination axis of the 17
correspondance analysis with no clear grouping of species. The main dominants were: Chrysanthemum coronarium, Achillea santolina, Convolvulus arvensis, Enarthrocarpus strangatulus and Avena fatua. Common annuals in the barley fields were, Trigonella maritima, Picris sprengeriana, and Lolium rigidum. Where soil is more compact and relatively saline, Reseda decursiva, Asphodelus tenuitolius, and Launaea resedifolia become more common (El Hadidi & Ayyad 1975). Floristic composition of the western Mediterranean coast The analysis of the flora of the Mediterranean and the categorization of the phytogeographical subdivisions of the flora of North Africa (Quezel, 1978) indicated that the flora of the western Mediterranean coastal of Egypt belongs to the “steppic Eastern – African domain, of the East Mediterranean sub region”. The Mediterranean region is classified, as a part of the “Mesogean subkingdom” of the “Holarctic kingdom”. The western Mediterranean coastal belt is by far the richest part of Egypt in its floristic composition owing to its relatively high rainfall. The number of species in this belt makes up about 50% of total Egyptian flora that is estimated to Boulos (1995). Most of these species are therophytes that flourish during the rainy season, giving the coastal belt a temporary showy grassland desert. During the longer dry period, only the characteristic woody shrubs and perennial herbs are evident; these constitute the scrub vegetation of the area, scattered sparsely in parts and grouped in denser more distinct patches in others (Tadros, 1956). Hassib (1951) describes the percentage distribution of both annual and perennial species among the life–forms in this coastal belt. Maquis vegetation that characterizes the other Mediterranean countries is not represented in Egypt .The prevailing life form of the perennials was chamaephytes; nanophanerophytes are less abundant. The floristic elements of the western Mediterranean coastal belt enjoy better climatic condition than those of the other parts of Egypt. There are more species and great numbers of individual plants and the vegetation is more or less continuous, not like that in the inland desert areas where the plant communities are separated by large stretches of barren ground. In the autumn numerous geophytes make an attractive show of flowers and in 18
late spring grasses and members of the Leguminosae, Compositae and Cruciferae are particularly abundant. Zahran & Willis (1992) reported that, xerophytes make up about (90%) of the total number of species in this coastal belt; most are therophytes (67%), followed by geophytes (11%), halophytes and helophytes (11%), chamaephytes (6.6%), micro and nanophanerophytes (3 %), parasites (1.2%) and stem scculents (0.1%). The common xerophytes include: Achillea santolina, Ammophila arenaria, Anabasis articulata, Euphorbia paralias, Gymnocarpos decander, Haloxylon scoparium, Helianthemum lippii, Retama raetam, Ononis vaginalis, Pancratium maritimum, Plantago albicans, Thymelaea hirsuta and Thymus capiitatus. Terrestrial halophytes include Arthrocnemum macrostachyum, Atriplex spp., Atriplex portulacoides, Halocnemum strobilaceum, Inula crithmoides, Juncus rigidus, Limoniastrum momopetalum, Nitraria retusa, Salicornia fruticosa, Suaeda fruticosa, Sueada pruinosa Tamarix nilotica, and Zygophyllum album. The helophytes and freshwater hydrophytes represent about (4%) of the total species of this coastal belt. They include: submerged species, e.g. Ceratophyllum demersum and Potamogeton crispus, floating species, e.g. Eichhorinia crassipes and Lemna spp, reed-like plants, e.g. Phragmites australis and Typha domingensis, and sedges, e.g. Cyperus spp, and Scirpus spp. El-Ghareeb & Rezk (1989) at a belt transect, 5 km broad and about 7 km long, extending from the Alexandria-Rosetta railroad at Bousseli town to the seashore reported a fourty-two perennial species, the most common perennial species are Echium sericeum, Echinops spinosus, Artemisia monosperma and Lotus creticus (recurrence> 60%). However, these species are not necessarily the most abundant in their stands. Less common perennials (recurrence>30%) is Launaea nudicaulis. The number of annuals encountered in this study was fifty-two, of which Rumex pictus, Plantago squarrosa var. brachystachys, and Daucus litoralis are recorded in at least 83% of the stands. Senecio belbeysius Reichardia tingitana and Mesembryanthemum crystallinum are recorded in at least 60% of the stands. Less common annuals are Aegilops bicornis, Centaurea glomerata, Conyza linifolia, Cutandia memphitica, Erodium gruinum, Erodium laciniaium, Ifloga spicata, Cakile maritima, Sonchus oleraceus and Salsola kali; each attains a recurrence of not less than 40%. The Life-form 19
spectrum of the study area reflects a typical desert flora. The majority of species are either therophytes (55.3%) or cryptophytes (perennial ephemerid herbs) (27.6%). The majority of other perennials in the study area are evergreen shrubs or sub-shrubs (chamaephytes, 11.7%). Hemicryptophytes (3.2%) and Nano-phanerophytes (2.1%). Abd ElSalam (1994) in her study at Omayed, El-Hammam, Burg-El Arab, Fuka and Maktella recorded 316 species 165 perennials, 151 annuals were distributed in the different habitats. The floristic surveys carried out in this study and in previous studies, indicated that the most striking observation is that the highest richness is recorded in non-saline depressions (113 prennial species and 111 annual species), and on ridges (102 prennial species and 104 annual species). This may be attributed to the remarkable heterogeneity in these two habitats. The study also reveals that the high species richness and diversity in these two habitats is again exhibited in the species richness and diversity of their communities. On the other hand the flora of salt marshes is very poor( 21 perennials and 9 annuals) since only a few species are adapted to physiological drought particularly where salinity is a limiting factor. Kamal & El-Darier (1995) recorded 91 species (52 perennials and 39 annuals) in the part of the western Mediterranean desert at about 65 km west of Alexandria. The most common perennials were Thymelaea hirsuta, Noaea mucronata, Deverra tortuosa, Echinops spinosus, Anabasis articulata and Anabasis oropediorum. The most common annual species were Lobularia arabica, Adonis dentatus,Filago desertorum, Picris radicata and Cutandia dichotoma. On the other hand there are some annual species of a very rare occurrence, e.g. Barassica nigra, Hypecoum aegyptiacum and Plantago notata. El Hadidi & Hosni (1996) recorded 1083 species from the Mediterranean coast. 255 species (including 18 endemics) with high percentage of annual (145 species or 57%). It has been noticed that 144 species are monogerial taxa to Mediterranean (120 species), SaharoSindian (14 species) and Irano-Turanian (10 species) elements, and another 80 species are Mediterranean taxa. Heneidy (2002) recorded eighty-two species (39 perennial and 43 annual) in the west of Alexandria, the most abundant life-form is the chamaephytes. The woody species Atriplex halimus is the most frequent indicator species (found in 59% of the sites) 20
in the study area. It followed by Asphodelus ramosus and Salsola tetrundra in 56 and 50% of the total sites respectively. EL-Dakak (2002) found in her study at rocky ridges in the western Mediterranean coastal desert 112 species (61 perennials and 51 annuals). In the same study she recorded the life forms; Nanophanerophytes, 6 species (5.3%), chamaephytes 20 species, (17.86%), hemicrptophytes, 24 species (21.42%)cryptophytes, 11 species (9.82%), therophytes 51 species (45.54). Hammouda et al. (2003) recorded 95 species (41 perennials 54 annuals) in the west Marsa Matruh area belonged to 30 families 75 genera and the life-form; therophytes (58%), chamaephytes (19%), hemicrptophytes (9%), geophytes (9%), and phanerophytes (5%). Heneidy (2004) recorded two hundred and thirty species belonging to 48 families in the western Mediterranean coastal land of Egypt. The families of high representation are Compositae (17%), Leguminosae (11.4%), Gramineae and Chenopodiaceae (10.5%) and (7.9%). 62 % of the studied species are common and about 24.9% are occasional, while 13% are rare. 60 % of the studied species are perennials (includes 1.8 and 12.7%, phanerophytes and geophytes, respectively) and 2.2% are biennials while, 40.2% are annuals. Plant Species mapping Studies on vegetation mapping in Egypt have characteristically been few e.g. Ayyad & Hilmy ( 1974) on parts of the Mediterranean costal belt. This lack of interest in vegetation mapping has been felt recently and a flurry of activity is currently surging among ecologists and plant geographers in Egypt. This is clearly evident by the recent activities of various researches in Egypt and their published scientific output Marri (2000) using the GIS techniques for vegetation mapping in Isthmic Desert at Sinai.
21
The Study Area 1- Location and Geomorphology The area selected for the present study lies between 25º 07ǯ – 26º 17ǯ of the Eastern Longitudes and 31º 36ǯ –31º 14ǯ of the Northern Latitudes (Map 3), and extends for about 121.5 km from Sallum on the Egyptian– Libyan frontier to El Bisri east Sidi Barrani on the Mediterranean coast with an average width varies between 2-36 km north-south direction. It thus comprises a total area about 4374 km2. Apart from the limited basement complex outcrops (gneisses and granites) in the southwest corner and in the southern parts along Latitudes 23º N, the western desert is mainly a sedimentary plain with Nubia Sandstones occupying the southern stretches. Cretaceous and Eocene limestone in the middle and Miocene-Pliocene limestone in northern stretches. As reported by Selim (1969), the entire northern region of the Western Desert is covered by sedimentary formations that range in age from lower Miocene to Holocene. The Holocene formations comprise lagoon and loamy deposits, sand dune accumulations, wadi fillings and limestone cists. Older formation (Pleistocene-Miocene) is of limestone or dolomite (dolostone). Taha (1973) distinguishes four major geomorphologic units in the landscape of the western province (between Ras El-Hekma and Sallum) of the western Mediterranean coastal land as follows: (1) narrow coastal plain (few meters to 1 km) of one oolitic limestone ridge, slightly dissected by drainage lines; (2) the narrow piedmont that merge gradually through the tableland and covered by a relatively thin mantle of alluvial deposits; (3) the tableland that tilting gradually toward the north and facing the Mediterranean Sea; and (4) the shallow simple drainage basins with slight meanders.
22
23
Map (3): Location map of the study area showing the different geomorphological units
In the study area, which lies between Sallum to Sidi Barrani; the cliff of the Diffa Plateau (southern table land) starts very close to the Sea at the western extremity of the area (Photo 1). A flat coastal land 2-4 km wide is found behind the ridge of dunes, starting some 10 km east of Sallum. The area between the coastal land and the plateau has rather pronounced relief with several terraces. There are a few large depressions along the edge of the plateau. One of the major physiographic features of western province is the presence of numerous wadis with peculiar physical features, and a characteristic plant cover. They have been scarcely explored. Each wadi may be physiographically distinguished into a plateau, slopes and wadi bed. The major feature of the plateau is the rocky surface. The upper positions of slopes are steep and completely devoid of soil cover. The middle position of slopes are less steep and covered by shallow soil mixed with fragments of different sizes, while the lower positions are gentle where deep soil accumulates by run-off water. 2- Soils The soils of the western Mediterranean coastal land of Egypt are young, and essentially alluvial. Diagnostic horizons are characteristically absent (Harga, 1967). They are derived from two main sources: (a) the Mariut tableland (inland plateau) composed essentially of limestone alternating with strata of limestone and shale, and (b) beach deposits composed of calcareous oolitic grains.
24
Photo (1): Sallum area.
Soils of the coastal ridge and dunes were loose or moderately consolidated calcareous grains of sand dimensions. They consist of about 90% or more of CaCO3, and are almost free from salts. On the slopes, the soils are pale brown and loamy in texture. On upper and middle parts, they are mixed with cobbles and gravels of various sizes throughout the profile. On lower parts, the surface is covered with relatively thick layers (2-5 m) of loamy soils washed down from higher levels. Soils of non-saline depressions are highly variable. In some parts, they are mainly calcareous, being derived from oolitic beach deposits. In other areas, alluvial loamy soils dominate. Near the seashore, low-lying soils may be mixed with latchstring saline silts and clays. Soils of lagoon salt marshes are of very shallow profiles usually covered with thin salt crusts. Transitional areas between ridges and depressions are covered with deep layers of down wash materials transported during the rainy season. In the southern part of the coastal plain, three main types of soils are recognized, belonging to the calcisols of a zonal soil groups. In one of these types, soils are moderately 25
affected by salts, and of pH values between 7.8 and 7.9. The CaCO3 content is 30-35%. In the second type, soils are characterized by the presence of gypsum together with lime accumulations. They are moderately affected by salts, and attain pH values between 8.0 and 8.2. The CaCO3 content is also 30-35%. The third type includes soils characterized by deep profiles with definite zones of lime accumulations at certain depths. The soils are fine textured, and are moderately affected by salts. Values of pH range between 7.9 and 8.1, and the CaCO3 content is little lower. The fourth main soils group distinguished in the area on the basis of geomorphologic features are the wind blown soils, the soils of beach plains and dune depressions, the soils of alluvial fans and outwash plain, and the rocky lands (Ghabbour, 1983). The winds blown soils are either coastal or inland dunes. The coastal dunes are composed mainly of oolitic sand and about 90% or more CaCO3, while the inland dunes consist mainly of quartz sand. The costal dunes consist of shifting oolitic sand and cemented oolitic sand. The shifting oolitic sand is predominantly deep and very loose, and forms the younger dunes. The cemented oolitic sand is composed of small grains of CaCO3 and forms the older dunes. Inland dunes are composed of oolitic sand and quartz sand. They are fixed by the vegetation, and have rather high values as rangeland and are probably suitable for a forestation. The Soils of beach plains and dune depression: These soils are found inland of oolitic sand dunes. They are well drained and deep, and their texture is sandy loam. In some areas, the beach plains are filled with weathered, loamy (oolitic) sand. They are areas of poorly drained, very saline soils. The well-drained soils are non-saline and are rather permeable. In general, they are suitable for cultivation of all crops. The poorly drained soils have a high ground water table (0-70cm), and are not suitable for agriculture. Soils of alluvial fans and outwash plains: have a very slightly sloping topography, and found mainly on the plateau and on the slopes of the Miocene rock. They may be classified as shallow, moderately deep and deep soils. The soils of the rocky land are less than 30 cm in depth, and are loamy sand to sandy loam over caliches layer or rock. They are not suitable for agriculture and are used as rangelands.
26
3- Water Resources The main water resources of the study area include rainwater and ground water. Water resources of surface runoff, and the runoff wadis are both products of rainfall and depend on its annual distribution and intensity (Photo 2, 3 and 4). Runoff water is utilized in three forms. The first takes place in depressions, where the topographical situation favors the accumulation of runoff of wadis or surface runoff from elevations. It is estimated that only 20% of total runoff of all wadis of the northwestern coast (about 11 million m3 / year) is utilized. The second form is achieved by constructing (a) dykes to prevent the flow of runoff of wadis to the sea, (b) dykes in the spreading zones, diverting the runoff of wadis, (c) transversal earth barrages to facilitate sedimentation and create terraces, which in general receive abundant runoff from wadis, and (d) small dykes parallel to the contour lines to retain the surface runoff. More than 3000 cisterns dating back to the Roman period exist along the western Mediterranean coastal of Egypt. Several hundreds of additional new cisterns have also been built during the last few decades. They provide the main drinking supply for the people and animals. Desalinization of seawater may become a major source in the future. Irrigation water is confined to the eastern part (Burg El Arab and El Hamam) and is brought by Bahig canal, and more water will be brought by the much larger Naser canal (27-37km south of the seashore). The ground water resources of the coastal zone were classified into 2 types by Paver and Pretorius (1954): (a) Structural perched water tables; located in certain small areas along the coastal zone. The intercalated limestone and clays are folded into gentle synclinal basins. Where the floors of such synclinal basins are overlain by limestone and where the fold has a closure above sea level, the conditions favors the development of self-contained perched water tables held above the main saline water table. Such basins are recharged by rainfall, which percolates through a lesser overall thickness of limestone, and consequently the salinity of the water in the basins will be lower than that of the underlying main water table in which the water has percolated through greater thickness of limestone. (b) The coastal dune water table; which have been drawn from the costal galleries suggest that water of these galleries owes its existence to some other features in addition to the proximity of the main 27
water table to the surface. The water supplies of the galleries owe their existence to a ground water mound in the main water table. 4- Human Activities In the study area, land use and grazing represent the most pronounced human activities. Two main types of agriculture are practiced rain-fed and pastoral. The principal crop cultivated by rain-fed farming is barley (Photo 5), tree crops of olives and figs are also grown without the aid of irrigation. The Bedouins who are settling permanently along the coastal tract cultivate both the cereal and tree crops. In good years when yields are sufficient to produce a surplus of grain, the surplus is stored under mounds of earth. Conversely in dry years when the rain is not sufficient to produce a crop, animals are allowed to graze on the shoots that emerge.
Photo (2)
28
Photo (3)
Photo (3-4): Torrent water in the delta of wadi Riqeit in Sallum area
Photo (4) : Surface runoff water in Sallum area.
29
The Bedouins of the coastal strip are famous for their pastoral way of life. Even though many Bedouins gave up their nomadic way of life and became sedentary, many still retain their flocks of camels (Photo 5 and 6), goods and sheep. Bedouins believe that the principal comicality, and form of status, and wealth has traditionally been the Bedouin’s herds of livestock. The result has been an increase in the number of livestock coupled with a decrease in the quality and area of the rangeland through the pressures of overgrazing, and the increased area of irrigated and reclaimed lands. FAO (1970) estimates that in the northwestern coastal region of Egypt, 70% of the population is involved in pastoral activity. These people are therefore very dependent upon the economic and ecological well being of the region. FAO (1970) estimates that a suitable carrying capacity for the region would be 25 fedden/animal, while the Egyptian Agricultural Department estimates that 50 feddens/animal would be more appropriate.
Photo (5): Barley fields in Sidi Barrani
30
Photo (6)
Photo (7)
Photo (6-7): Poor grazing potential in Sallum area. 31
5- Climate The western Mediterranean coast of Egypt lies in Meig’s ‘‘warm coastal deserts” (Meigs, 1973): summer’s warmest month with mean temperature less than 30 ºC, and winter’s coldest month with mean temperature above 10 ºC; though occasional short rain storms occur in winter, but most of the days are sunny and mild. From the map of the world distribution of arid regions (UNESCO, 1977) the climatic conditions are: warm summer (20 ºC to 30 ºC), mild winter (10 ºC to 20 ºC), and P/E+P less than 0.03 (where P is annual precipitation and E is annual evaporation). It is suggested that three main factors contribute to make up the climate: A-The situation with regard to the general circulation of the atmospheres; B-The proximity of the Mediterranean Sea; and C- The orientation of the coast. The first factor is the most important. In general, the weather is controlled in summer by the subtropical high-pressure belt, and in winter by the cyclones moving eastwards with the waster lines. The proximity of the sea has a direct effect on temperature and humidity, and consequently on evaporation and condensation, but not on the amount of rainfall. The orientation of the coast with regard to the prevailing wind probably provides the explanation for differences in the distribution of rainfall along the coast. The general feature of the climate of the study area may be approximated from the data obtained from the Egyptian Meteorological Authority. These climatic data were collected at Sallum and Sidi Barrani Stations, and at Mersa Matruh and Alexandria for comparison. 5-a. Rainfall The local orientation of the northwestern coast relative to the direction of the moist air currents affects largely the amount of rainfall to such an extent that it may in one place exceed double the amount in another place very close to it. The monthly rainfall varies greatly. At any station on the western Mediterranean coast the rainfall is heaviest in the months of November to February while the months June, July and August are virtually dry. The 32
maximum amount is received during either January or December and varies considerably between different station (Table 1). At Sallum, it amounts to 21.6 mm in January and 18.4mm in December, while at Sidi Barrani it is 42.4 mm in January and 37.4 mm in December. Similarly, the total amount of annual rainfall varies between different stations with a maximum of 199.4 mm at Alexandria and a minimum of 101.1 mm at Sallum Fig (1). 5-b. Air Temperature It is clear from data in Fig (2) that the annual mean air temperature decreases from the west at Sallum (26.6 ºC) to the east up to Mersa Matruh (19.4 ºC), and then increases again towards Dekheila (20.2 ºC). The mean maximum air temperature varies from 17.7 ºC in January at Dekheila and Sidi Barrani to 31.2 ºC in August at Sallum. Also, the mean minima are not so low to inhibit growth or prevent germination Table (2). The lowest mean minimum ranges between 8.4 ºC in January at Sidi Barrani and Mersa Matruh to 23.5 ºC in August at Dekheila. Such noticeable variability between the mean maximum and minimum degrees of temperature will have certain biotic impacts on plant and animal life and certain a biotic impacts on erosion of rocks and geo-pedological processes. The differences between monthly means of air temperature are of narrow range as compared with those in inland western desert, e.g. in Bahariya Oasis it ranges from 0 ºC in January to 47.5 ºC in August. 5-c. Relative Humidity This factor has its paramount effect on the conditions of the vegetation, through its effect on the water economy of plants. Generally, as it is evident from Table (3), the weather is very humid and the plants are subjected to high values of atmospheric humidity all the year round. The monthly mean relative humidity is usually higher in the summer months (June- August) than in the winter months (December-March). It ranges between 51% in November at Dekheila and 75% in July at Sidi Barrani. Regarding the mean annual, records of Sallum was the lowest (61.2 % and at Sidi Barrani was the highest (67.6 %) Fig. (3). A remarkable feature of the relative humidity in the study area, and in the Mediterranean Coast 33
region of Egypt, is that it ten do to be higher in summer than in winter (Migahid et al., 1955, 1963 and 1975). 5-d. Wind Speed and Direction Winds in the western Mediterranean coast of Egypt are generally light, but violent dust storms and sand pillars are not rare. Dry hot dust-laden winds from the south known as khamasin blow occasionally for about 50 days during spring and early summer. At Mersa Matruh and Sidi Barrni, wind strongly during winter and early spring, with an average velocity of about 18.68 to 22.57 km/hr. (Table 4). The end of summer recorded many calm days and the average speed drops to 15 km/hr. The wind speed at Alexandria and Sallum is about 25% lower than in Mersa Matruh and Sidi Barani. Figures (4 and 5) showed that the prevailing wind direction is the northwest to west at Sallum and Sidi Barrani.
34
Jan
15.6
21.6
30.5
42.4
27.10
33.2
48.3
54.9
Station
Sallum(1946-1960)
Sallum (1968-2002)
Sidi Barrani (1952-1960)
Sidi Barrani (1968-2002)
Mersa Matruh (19471960)
Mersa Matruh (19481975)
Alexandria (1942-1960)
Alexandria (1946-1975)
26.6
28.4
15.1
16.4
18.1
7.4
13.0
7.1
Feb
12.9
14.0
12.0
13.7
14.8
11.4
8.8
13.6
Mar
4.2
2.7
2.8
2.3
6.2
1.3
4.0
0.6
Apr
35
1.5
1.5
2.6
3.2
3.0
5,2
2.9
4.3
May
Tr.
Tr.
2.0
Tr.
0.2
Tr.
0.4
Tr.
Jun
Tr.
Tr.
Zero
Zero
Tr.
Tr.
Tr.
Tr.
Jul
0.3
0.5
0.6
Zero
0.2
0.4
Zero
Zero
Aug
1.0
0.4
1.1
0.6
1.4
0.1
1.7
0.9
Sep
9.3
7.9
15.6
15.4
21.5
19.0
13.2
17.5
Oct
33.1
32.2
22.5
26.7
20.5
23.2
17.1
39.7
Nov
55.6
56.2
30.2
38.7
37.4
40.0
18.4
20.4
Dec
199.4
192.1
137.7
144,1
165.7
138.5
101.1
119.7
Total
Table (1): Monthly averages of rainfall (mm) at Sallum and Sidi Barrani stations on the Mediterranean coast, together with another two stations for comparison. Tr = Traces.
Dekheil a (1461975)
Mersa Matruh (19461975)
Sidi Barrani (19682002)
Sallum (19682002)
Station
M
M
18.5
17.7
18.0
17.7
13.60
9.6
13.20
8.4
13.05
8.4
13.95
9.4
Jun
m
M
19.4
14.40
18.6
13.70
18.8
13.70
18.5
14.65
10.3
8.6
8.9
9.9
Feb
m
19.8
20.4
20.7
16.20
12.0
15.40
10.2
15.51
10.5
M
21.1
16.2
11.3
Mar
m
M 23.8
22.1
22.7
23.1
18.2
14.5
17.40
12.1
17.50
12.9
18.75
13.7
Apr
M
M 26.5
24.2
25.4
25.1
21.00
16.9
20.00
14.7
19.95
15.7
21.60
16.7
May
m
M 30.4
27.1
28.1
27.8
24.2
20.7
23.20
18.4
23.20
19.3
25.15
19.9
Jun
m
28.1
29.1
28.1
25.40
22.7
24.80
20.4
24.95
21.8
36
M 31.1
26.35
21.6
Jul
m
M 31.2
28.9
28.7
29.5
26.50
23.5
29.40
21.1
25.50
22.1
26.60
22.0
Aug
m
M 29.7
28.0
28.6
28.8
25.50
22.2
24.20
19.7
24.15
20.3
25.20
20.7
Sep
m
M 27.4
26.3
26.9
26.1 22.40
18.7
21.90
16.9
21.75
17.2
23.30
18.2
Oct
m
M 24.1
22.9
23,2
23.4 19.40
15.4
18.30
13.4
18.25
13.6
19.49
14.7
Nov
m
M 20.1
19.2
23.2
19.9 15.60
11.3
14.80
10.1
14.60
10.0
15.65
11.2
Des
20.20
19.69
19.34
20.57
Annua l
Table (2): Monthly mean minimum (m) and mean maximum (M) air temperature (°C) at Sallum and Sidi Barrani on the western Mediterranean coast, together with another two stations for comparison.
0
20
40
Sallum
Barrani
Matruh Alex.
Stations
Alexandria (1946-1975)
(1948-1975)
Alexandria (1942-1960)
60
(1947-1960)
Mersa Matruh
Mersa Matruh
Sidi Barrani (1968-2002)
Sidi Barrani (1952-1960)
Sallum (1968-2002)
Sallum (1946-1960)
80
100
120
160 140
180
200
37
Fig. (1): Annual rainfall (mm) at Sallum and Sidi Barrani stations on the Mediterranean coast, together with another two stations for comparison.
Annual rainfall (mm)
Fig. (2):
Annual mean temperature ( °C)
Barrani
Stations
Matruh
Sallum
Dekheila (146 -1975 )
Mersa Matruh (1946 -1975 )
Sidi Barrani (1968 -2002 )
Sallum (1968 -2002 )
38
Annual mean air temperature (°C) at Sallum and Sidi Barrani on the western Mediterranean coast, together with another two stations for comparison.
18.6
18.8
19
19.2
19.4
19.6
19.8
20
20.2
20.4
20.6
Dekheila
65
63
68
Sidi Barrani (1968-2002)
Mersa Matryh (1946-1975)
Dekheila (1946-1975)
64
63
62
59
Feb
63
61
63
58
Mar
64
63
63
58
Apr
67
67
70
60
May
69
69
71
60
Jun
72
73
75
64
Jul
69
70
74
66
Aug
65
68
69
65
Sep
68
65
68
63
Oct
51
66
66
61
Nov
65
64
65
60
Des
65.42
66.00
67.58
61.25
Annual
15.72 18.68 20.72
15.72
22.01
15.91
Sidi Barrani (1946-1975)
Mersa Matruh (19461975)
Alexandria (1946-1975)
Feb
22.20
Jun
18.13
Month
Sallum (1946-1975)
Station
16.83
21.27
21.45
16.65
Mar
15.35
19.39
22.57
14.98
Apr
14.61
17.20
18.50
13.50
May
39
14.98
18.50
17.02
15.54
Jun
15.72
18.31
20.72
16.65
Jul
15.24
18,65
15.54
16.09
Aug
12.58
15.91
14.80
13.87
Sep
11.28
15.17
15.54
12.21
Oct
12.21
17.30
19.42
14.06
Nov
13.87
20.53
21.46
16.61
Des
14.53
18.75
18.99
15.33
Annual
Table (4) : Monthly mean wind speed (km/hr) at Sallum and Sidi Barrani on the Mediterranean coast, together with another two stations for comparison.
61
Jan
Sallum (1968-2002)
Station
Month
Table (3) : Monthly mean of relative humidty (%) at Sallum and Sidi Barrani on the westren Mediterranean coast, together with another two station for comparison.
58
59
60
61
62
63
64
65
66
67
Barrani
Stations
Matruh
Sallum
(1946-1975)
Dekheila (1946-1975)
Mersa Matryh
Sidi Barrani (1968-2002)
Sallum (1968-2002)
40
Fig. (3): Annual mean of relative humidity (%) at Sallum and Sidi Barrani on the western Mediterranean coast, together with another two stations for comparison.
Annual mean relative humidity (%)
68
Dekheila
41
Fig. (4): Winds Rosa of the Sallum area showing the wind speed and direction for 34 years ago (1968 – 1994, 1982 – 2002).
Annual mean wind speed = 15.33 km / hr
42
Fig. (5): Winds Rosa of the Sidi Barrani area showing the wind speed and direction for 34 years ago (1968 – 1994, 1982 – 2002).
Annual mean wind speed = 18.99 km / hr
Material and Methods 1- Selection and distribution of stands Having a reasonable degree of plysiognomic homogeneity in topography and vegetation type, low levels of vegetation disturbance, and changes in habitat types and plant communities were the main criteria in selection of stands. Therefore, stands in the study area were randomly distributed. After a reconnaissance survey, that was conducted between 2002 and 2003, 133 stands were selected to represent as much as possible the variation in the vegetation and georeferenced using GPS model Trimble SCOUTm. Location and co-ordinates of these stands, together with their geomorphologic landscape units were presentend in (Table 5 ), Map (4)
Table (5): Location and co-ordinates of stands, and their geomorphologic landscape Stand number
North
East
Degrees Minutes Seconds Degrees Minutes Seconds
Geomorphologic landscape
1
31
31
89
25
10
26
Salt marsh
2
31
31
86
25
10
25
Rocky land
3
31
30
98
25
11
79
Sand sheets
4
31
30
96
25
12
63
Salt marsh
5
31
30
99
25
12
64
Salt marsh
6
31
30
71
25
14
52
Coastal rocky ridge
7
31
28
59
25
13
98
Desert plains
8
31
28
62
25
17
16
Rocky ridge
9
31
28
13
25
19
2
Rocky plain
10
31
27
95
25
21
2
Sand sheets
11
31
27
58
25
20
75
Rocky plain
12
31
26
0
25
20
0
Desert plain
13
31
25
0
25
18
0
Rocky ridge
14
31
23
50
25
19
37
Sand plain
15
31
29
50
25
22
0
Salt marshes
16
31
27
68
25
24
78
Rocky ridge
17
31
27
82
25
24
91
Gravel desert
43
18
31
28
13
25
25
10
Salt marsh
19
31
30
0
25
25
0
Salt marsh
20
31
28
6
25
24
15
Costal rocky ridge
21
31
30
50
25
24
0
Salt marsh
22
31
27
42
25
24
90
Rocky plain
23
31
25
93
25
25
11
Gravel desert
24
31
25
50
25
24
50
Gravel desert
25
31
26
30
25
25
63
Sand plain
26
31
25
47
25
25
77
Sand plain
27
31
25
27
25
25
78
Gravel desert
28
31
18
46
25
25
68
Gravel desert
29
31
19
50
25
22
0
Shallow wadi
30
31
18
50
25
21
0
Shallow wadi
31
31
19
50
25
21
0
Slope of ridge
32
31
20
0
25
20
50
Sand soil
33
31
28
0
25
27
0
Desert plaines
34
31
27
0
25
28
0
Gravel desert
35
31
24
50
25
30
0
Gravel desert
36
31
23
50
25
26
50
Gravel desert
37
31
21
0
25
30
0
Gravel desert
38
31
20
50
25
29
0
Gravel desert
39
31
20
0
25
28
0
Sand plain
40
31
21
50
25
25
50
Sand plain
41
31
20
50
25
25
0
Rocky land
42
31
19
50
25
27
0
Rocky land
43
31
19
0
25
27
0
Slope of ridge
44
31
18
0
25
26
50
Rocky land
45
31
18
50
25
25
0
Shallow wadi
46
31
29
50
25
28
50
Salt marsh
47
31
30
0
25
27
50
Salt marsh
48
31
30
50
25
27
0
Salt marsh
49
31
29
50
25
33
0
Desert plain
50
31
27
0
25
33
0
Gravel desert
51
31
26
0
25
33
50
Gravel desert
52
31
25
0
25
32
0
Gravel desert
53
31
24
0
25
33
0
Gravel desert
44
54
31
24
0
25
34
0
Rocky land
55
31
22
0
25
32
50
Gravel desert
56
31
19
0
25
31
0
Gravel desert
57
31
16
50
25
28
50
Shallow wadi
58
31
16
0
25
28
50
Wadi delta
59
31
17
50
25
28
0
Gravel desert
60
31
19
50
25
28
0
Gravel desert
61
31
30
57
25
31
68
Salt marsh
62
31
31
19
25
31
37
Sand dunes
63
31
35
0
25
54
0
Waste land
64
31
34
0
25
53
0
Waste land
65
31
33
30
25
52
88
Waste land
66
31
31
57
25
51
11
Waste land
67
31
30
93
25
49
35
Sandy hills
68
31
28
79
25
46
48
Sandy hills
69
31
28
13
25
45
80
Gravel desert
70
31
35
96
25
58
19
Gravel desert
71
31
36
69
25
59
16
White sand dunes
72
31
36
9
26
0
45
Salt marsh
73
31
36
36
26
0
81
White sand dunes
74
31
35
19
25
59
32
Sand sheets
75
31
33
36
25
47
71
Sand sheets
76
31
31
22
25
48
0
Sand sheets
77
31
29
87
25
48
21
Sand sheets
78
31
28
82
25
48
63
Gravel desert
79
31
28
9
25
45
59
Sand plain
80
31
27
86
25
43
74
Sand plain
81
31
26
69
45
41
65
Gravel desert
82
31
24
48
25
41
2
Gravel desert
83
31
20
37
25
39
68
Gravel desert
84
31
15
24
25
38
14
Gravel desert
85
31
14
10
25
38
53
Shallow wadi
86
31
34
96
25
46
44
Salt marsh
87
31
35
78
25
46
29
Salt marsh
88
31
35
94
25
46
34
Coastal ridge
89
31
32
64
25
42
22
Sand plain
45
90
31
33
82
25
42
10
Salt marsh
91
31
34
9
25
41
88
Salt marsh
92
31
34
47
25
41
89
Rocky ridge
93
31
34
31
25
9
2
Rocky ridge
94
31
34
26
25
7
95
Rocky ridge
95
31
34
26
25
7
95
Rocky ridge
96
31
28
97
25
15
40
Rocky land
97
31
29
85
25
38
31
Sand sheet
98
31
29
30
25
36
89
Sand sheet
99
31
28
6
25
36
23
Gravel desert
100
31
26
7
25
35
43
Rocky land
101
31
22
66
25
33
39
Rocky land
102
31
20
80
25
30
2
Rocky land
103
31
17
2
25
28
89
Shallow wadi
104
31
33
17
26
4
94
Waste land
105
31
31
58
26
4
80
Waste land
106
31
30
7
26
5
83
Sand dunes
107
31
29
26
26
4
25
Sand dunes
108
31
25
99
26
3
78
Salt marsh
109
31
21
66
26
5
65
Gravel desert
110
31
20
36
26
6
29
Rocky land
111
31
22
9
26
7
23
Gravel desert
112
31
30
80
26
13
7
Sand dunes
113
31
33
12
26
14
56
White sand dunes
114
31
26
32
25
49
7
Sandy rocky land
115
31
26
50
25
48
56
Sand sheets
116
31
25
27
45
49
0
Sandy gravel land
117
31
23
0
25
49
46
Sandy rocky land
118
31
22
56
25
50
24
Gravel desert
119
31
20
3
25
51
39
Rocky land
120
31
20
52
25
54
0
Rocky land
121
31
22
58
25
54
57
Rocky land
122
31
23
12
25
55
30
Rocky land
123
31
25
4
25
54
13
Gravel desert
124
31
27
33
25
54
58
Rocky land
125
31
28
52
25
55
59
Rocky land
46
126
31
32
9
26
6
30
Waste land
127
31
30
4
26
6
39
Waste land
128
31
26
31
26
6
13
Rocky land
129
31
25
18
26
7
43
Gravel desert
130
31
24
50
26
7
22
Gravel desert
131
31
21
56
26
9
2
Rocky land
132
31
25
24
26
15
35
Rocky land
133
31
28
17
26
15
46
Rocky land
2- Floristic features The floristic composition of a community is an indication of species coexistance. In each of the studied stands, ecological notes, presence or absence of plant species were recorded. The recorded taxa were classified according to the life-form system that proposed by Raunkiaer (1937) and Hassib (1951). The number of species within each life form category was expressed as a percentage of total number of species in the study area. Analysis of phytogeographical ranges was caried out using Zohary (19661972), Abd El-Ghani (1981 & 1985) and Khedr (1999). Taxonomic nomenclature was according to Tăckholm (1974), Cope & Hosni (1991), Boulos (1995, 1999, 2000, 2002) and El Hadidi & Fayed (1978,1995). Voucher specimens of each species were collected, and identified at the Herbaria of Cairo University (CAI) and Assiut University (ASI), where they were deposited. A complete checklist of the recorded species, together with their life formes and phytochoria were presented in the appendices. Vegetation sampling A quantitative survey of the vegetation of the study area that located between Sallum on the Egyptian-Libyan frontier and El Bisri east of Sidi Barrani (25º 07’-26º 17’ E- 31º 36’- 31º 14’ N ) on the Mediterranean coast was undertaken. It extands for a distance of about 121.5 km, and a total of 4374 km2. A reasonable distance (100-150 m) away from the high way was ensured in each stand to eliminate any distrubance which may have been caused to the vegetation. 133 stands (20 X 30 m) were selected for this analysis Fig (6). Stratified random sampling method was employed ( Greig - Smith, 1983;Ludwing & Keywords, 1988). 47
Map (4): Location map for 133 investigated stands in the study area.
For each stand, a floristic- count list was taken from five 25 m2 each quadrat. In each quadrate, the occurrence and the number of individuals of each presented species were recorded, and then used to calculate absolute density and frequency of the encountered perennial species. In each stand, the plant relative cover was determined using line-intercept method (Canfield, 1941). For this purpose, five parallel lines (20 m each) were laid across the stand and the intercept lengths (cm) of each perenninal species were summed. The lengths of intercept of each presented species in a stand were measured to the nearest cm along the five line transects. These lengths were then summed and expressed as a relative value of the total lengths of the five transects. The annual plant species were also recorded within each stand, but excluded from the analysis (See Photos in the appendices). The following formulas were used for vegetation determinants (see Müller-Dombois & Ellenberg, 1974) : % Frequency of each species = Total number of quadrats in species occurrence / All number of studied quadrats x 100 Relative frequency = % frequency of species / Sum of frequency precentages of all species x 100 Absolute density = Total number of individuals of species / All numbers of quadrats studied 48
Relative denisty = Denisty of species / summation of denisty of all species x 100 Cover = Total of intercept lengths for a species / Total transect length x 100 Relative cover = Total intercept lengths for a species / Total of intercept lengths for all species x 100 Importance Value = Relative frequncy + Relative denisty +Relative cover 30 m
5
5 m 5
20 m
5
5 m 5
5 5 m
5 5 m
Fig (6): Diagram of minimal area in which five samples five intercept lines represented.
4- Soil analysis Three soil samples were collected in each stand to (0-30 cm) depth or the parent rock level for shallow soil. The three samples of each stand were mixed together. Part of soil sample was used to determine its total moisture content; soil was weighed in altared aluminum container placed in an oven dried to constant weight at 105 ºc. Then the sample was reweighed and the content of moisture was expressed as a precentage of the oven dry weight (Allen et al., 1974 ). Soil moisture content (MC) was calculated as percentage according to the follwing equation: MC = Loss in wt on drying (g) / Initial sample wt (g) x 100 49
Another part of soil samples were air-dried (spreaded over sheets of paper and left to dry in air). Dried soils were passed through 2mm sieve and packed in plastic bags till analysis. 4-1 . Soil physical characters 4-1-1 . Soil texture Soil texture was determined by the pipette method , where percentages of sand, silt and clay were calculated. The air dried fine soil generally includes structural aggregates as well as altimate particles, and dispereal of aggregates was made by adding 1N sodium hexamelaphosphata (Calgon solution) as a dispersing agent (Jackson, 1967). The objective was to ensure that all primary particles were dispersed in the suspension but without too vigorous handling which could break those down from their original size to smaller size during the treatment. Pipette samples were taken after 40 seconds and 2 hours providing data on the content of sand, silt and clay fractions. 4-2 Soil chemical analysis Soil extracts were prepared 1:5 (W/V) soil / distilled water to meet the requirement for different determinations. 4-2-1 Determination of soil reaction (pH) pH value of the soil extract were determined by an electric pH meter with a glass electrod in a soil / distilled water suspension ( 1: 5 ). The pH meter was calibrated before each measurement. 4-2-2 Electric conductivity and total dissolved salts The specific conductivity (Ec), was measured in an conductivity cell by a low voltage A.C. wheatstone dridge Ec meter as described by Allen et al., 1974). The total Dissolved salts colculated as percentage according to the following equation: T.D.S = Ec x 0.32 =…% 4-2-3 Determination of total carbonate Total carbonates were estimated according to Jackson (1967). Five grams of soil were placed im 200 ml- conical flask. A 100 ml 1N HCl were added. The flask was covered and stirred vigorously several times during a peroid of 1h. Twenty ml of the supernatent liquid were taken and few drops of ph.ph indicator added. The mixture was titrated against 1N 50
NaOH. 20 ml of 1N HCl were titrated against 1N Na OH (V blank) Data were calculated and expressed as g % ( Allison & Moodie, 1965 ). 4-2-4 Determination of Sodium and Potassium Na+ and K+ were estimated by a Drlang M 7 D Flame photometer with acetylene or propane burner. 4-2-5 Determination of Calcium and Magnesium Ca++ and Mg++ were estimated using a Buck Scientifi model 210 VGP atomic absorption spectrophotometer. 4-2-6 Determination of Organic matter Organic matter was estimated by the Walkly –Black titration method wet combustion method (Tan, 1996) using K2Cr2 O7 and H2SO4 to estimate the decomposed fraction of soil organic matter . 5-Data analysis: Multivariate analysis 5-1 Calssification of stands The basic purposes of multivariate analysis are (1) summarizing large complex data sets, (2) aiding the environmental interpretation and hypothesis generation about community variation and elucidating the phytosociological behavior of the common species, and (3) refining models of community structures. ( Moustafa, 1990 and Ward et al. 1993). In order to obtain an effective analysis of the vegetation and related environmental factors, both classification and ordination tecniques were employed. Unicates of the total flora were eliminated from the data set to avoid noise and summarize redundancy (Gauch, 1982 ).Three data matrix were used: (1) in Sallum area; 55 species and 53 stands. (2) in Sidi Barrani area; 31 species and 65 stands. (3) in the whole study area; 51 species and 133 stands. Each floristic matrix was then subjected to classification by Two Way Indicator Species Analysis (TWINSPAN) using the default settings of the computer program PC-ORD for windows version 4.14 ( McCune & Mefford, 1999). 51
TWINSPAN is a FORTRAN program for arranging multivariate data in an ordered two-way table by classification of the samples and species. It is a robust technique because it is fairly impearmeable to sample errors or noise ( Gauch & Whittaker, 1981). The samples are ordered first by divisive hierarchical clustering, and then the species are clustered based on the classification of samples. An ordered two-way table that expresses succinctly the relationships of the samples and species within the data set is constructed (Hill, 1979). In the output, the hierarchy is shown in binary notation along the right-hand and bottom margins numbers and names of species, and numbers of samples, are shown along the left- hand top margins. Values denote categories of abundance defined by the pseudospecies cut levels. TWINSPAN also identifies “ indicator species” which differntiate the sample- groupings at each level of division. The resulting dendrogram was interpreted with respect to field observations and measured environmental variables, with described groups being derived from several levels in the hierarchy. 5-2. Ordination The basic goal of ordination is to summarize the community patterns, and to compare these with the environmental information in order to produce an environmental information. In this study, the default option of the computer program CANOCO software version 3.12 (Ter Braak, 1987a, 1990 ) was used for all ordinations. Two types of ordination were used: 5-2-1 Indirect gradient analysis The indirect gradient analysis was undertaken using Detrended Corresponding Analaysis (DCA; Whittaker, 1967 ). DCA ordinates both samples in terms of species and species in terms of samples in which they occur from the same two-way data matrix and plots the same results on the same set of axes. Four principal axes are given of which any two or three can be used to produce the ordination plane. Usually, the first two axes represent the highest proportion of the variabilty in the data set, expressed in terms of eigenvalues. It can produce overlays of environmental data relevant to the sampling plots to look for trends of variation in the 52
vegetation and environmental. (Samples = stands in this study ) that are more similar in vegetation structure (species composition and abundance) were depicted as being closer together in the ordination diagrame. Stands that differ by four standred deviations (4.5.D., the axes units) in score can be expected to have no species in common (Ter Braak, 1987 b). Preliminary analyses were made by applying the default options of the DCA (Hill & Gauch, 1980 ) in the CANOCO program, to check the mangnitude of change in species composition along the first ordination axis (i.e., gradient length in standard divation units ). DCA estimated the compositional gradient in the vegetation data of the present study to be larger than 6.0 S.D units for all subset analysis, thus Canonical Corrspondence Analysis (CCA) is the appropriate ordination method to perform direct gradient analysis (Ter Braak & Prentice, 1988). 5-2-2. Direct ( constrained) gradient analysis Økland (1996 ) summarized the advantages of using constrained ordination analysis as follows: 1) Easy access via the programe package CANOCO. 2) Growing awareness of defects in an available ordination techniques. 3) Its intuitive appeal by relating vegetational variation directly to environmental factors. 4) Circumvention of the tedious interpretation process necessary with ordination. 5) Easy access to joint plots (with species and / or samples and vectors representing the direction of maximum change in each external variable ) in CANODRAW, a plotting program issued with CANOCO. Canonical Correspondunce Analysis (CCA) is a multivariate analysis technique developed to relate community composition to known variation in the environment. It is a correspondence analysis which the axes were chose in the light of the environmental variables (Ter Braak, 1986). In CANOCO, ordination axes chosen in the light of known environmental variables by imposing the extra restriction that the axes be linear combinations of environmental variables, i.e. direct gradient analysis (Ter Braak, 1986). Direct gradient analysis is that species composition is directly and immediately related to measured environmental variables. The most common algorithm for CCA involves the addition of steps to CA. 53
The new steps are added to take advantage of supplemental data in the form of environmental variable. A multiple linear least-squares regression is performed with the site scores (determined from weighted averages of species) as the dependent variables, and the environmental variables as the independent variables. New site scores are then assigned as the value predicted using the regression equation. The relationships between vegetation gradients and the studied environmental variables can be indicated on the ordination diagram produced by CCA ( biplot or controids). The variables in the CCA biplots are represented by arrows pointing in the direction of maximum variation, with their length proportional to the rate of change (Ter Braak, 1986). Each arrow determines an axis on which the species point can be projected. When plot points are projected perpendicularly to the (prolonged) arrows, their order represents approximately the ranking of weighted averages with respect to the values of the factores involved. Ter Braak (1986) suggests using DCA and CCA together to see how much of the variation in species data is accounted for by the environmental data. A Monte Carlo permulation test (99 permutations; Ter Braak,1990) is used to test for significance of the eigenvalues of the first canonical axis. The use of canonical coefficients in determining the significance of environmental variable is undesirable because they can be unstable. Intra – set correlation from the CCA,s are therefore used to assess the importance of the environmental variables. All data variables are assessed for normality (SPSS for windows ver. 10.0), and appropriate transformations are performed. Fourteen environmental variables are included: sand, silt, clay, soil reaction (pH), organic mattter (OM), electric conductivity (EC), total soluble salts(TSS), moisture content (MC), total carbonate(CaCO3), Sodium (Na+) Potassium (K+) , Calcium (Ca++), Magnesium (Mg++) and alitude (Alt). The TWINSPAN vegetation groups are subjected to an ANOVA (OneWay Analysis of Variance ) based on soil variables to find out whether these are significant variations among groups. Analysis of variance provides an insight into the nature of variation of natural events, which is possibly of even greater value than the knowledge of the method as such (Sokal& Rohlfs, 1981). Pearson’s product-moment correlation coefficient is calculated to evaluate the relationship between the environmental parameters, and Sorensen’s coefficient of floristic similarity (CCs) 54
between the TWINSPAN vegetation groups is also determined. The latter analysis are calculated with the GLM (General Linear Model) procedure available in the program SPSS for windows version 10.0 . Schematic presentation of the methodology that followed in this study is given in fig. 7.
Floristic List
Life Form
Phytochoria
Distribution of species in units
Final Floristic List Table (6)
Fig. (7): Diagrammatic sketch for the stages of the data analysis.
(1) List of field Cover
List of field Density + Frequency (quadraits)
(line intercept method)
Calculated
Sp. ----------
Relative Frequancy -------------------------------
Relative Denisty ------------------------------¦
Cont. Fig. (7): Vegetation Analysis 55
Relative Cover ----------------------------------------
= IV (Importance value)
(2)
IV Enter data to Excel:
Sp.
St 1
----------
IV
---------
St 3
St 4
------ ---------- ---------- -----
St 2
-------------
Enter data to the P C-O rd program :
O utput of TW INS P AN (Tw o W ays Indicator Species Analysis)
(3)
S am ples of so il:
D raw in g diagram
Soil analysis
T W IN S P AN group s
Locate grou ps in the stud y area m ap
S t. S o il variab le G rou p s ----------------
Cont. Fig. (7)
56
---------------------
----------------
-----------
A C A D F
(4) SPSS Program
CANOCO Program
Table of groups / soil variable
CCA
DCA
(Canonical Correspondence Analysis)
(Detrended Corresponding Analysis)
Table
Diagram
Table
Diagram
Cont. Fig. (7)
Plant species mapping Among the recent advances in geographical methodology and mapping is the technique of geographical information system, shortly known as GIS. It is not the intention of this study it develop into the technicalities of this system, sufficient here to refer to the recent treatise by Worboys (1995). However, it might be desirable here to give some remark about such specification of this technique that might be pertinent to the purposes of this study. A Geographical Information System (GIS) is a computerbased information system that enables capture, modeling, manipulation, retrieval, analysis and presentation of geographically referenced data. Other definition : GIS is a powerful set of tools for collecting, storing, retrieving as will, transforming and disply spatial data from the real world for a particular set of purposes. This system employs a number of satellites orbiting the earth and covering its entire surface area. Each of these satellites is provided with a data base and appropriate software so that 57
when a signal emanates from a certain point on earth it is received by a number of these satellites, and the geographical coordinates of that point are computed and retransmitted to that same point where it can be received by a small electronic unit know as the Global Positioning System (GPS). The global positioning system (GPS) is a set of satellites in geostationary earth orbits used to help determine geographical location anywhere on the earth by means of portable electronic receivers. The study of GIS has emerged in the last decads as an exciting multidisciplinary endeavor, 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 (Peter & Rachael, 1998).
Results Floristic diversity A total of 219 species (116 annuals and 103 perennials), belonging to 154 genera and 47 families were recorded. The largest families were Asteraceae (36 species), Fabaceae (32 species), Brassicaceae and Poaceae (17 species for each), Chenopodiaceae (16 species), Boraginaceae (9 species) and Caryophyllaceae (7 species). They constituted about two-third (61.19%) of the recorded species, and represent most of the floristic structure in the Mediterranean North African flora (Quézel, 1978). Nineteen families were represented by only one species, and eight families were represented by two. Five families were represented by three species (Cistaceae, Malvaceae, Plantaginaceae, Polygonaceae, Solanaceae), and five families were represented by four species, (Apiaceae, Euphorbiaceae, Lamiaceae, Plumbaginaceae, Scrophulariceae). Three families were represented by five species (Geraniaceae, Liliaceae, and Zygophyllaceae,). These families altogether constituted (22.83 %) of the recorded species. The largest genera include Astragalus (10 species), Centaurea, and Erodium (5 species for each), Euphorbia and Lotus (4 species for each). Nine genera were represented by three species, twenty-four genera were 58
represented by two species, and one hundred and sixteen genera were represented by only one species. Though floristic similarities prevail among the different stands of the study area, the floristic composition and vegetation structure showed perceptible variations within each stand (Appendices). Boulos (1995) cited 1095 species recorded along the Mediterranean coastal region of Egypt. In the present study, the recorded species represent 20% of the total flora of the region. It was also noted that the generic index 219/154 was 1.42. Locally this ratio is in accordance with the observation of Zohary (1973) “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 in floral accumulation and differentiation centers. Five main geomorphologic 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, (Map, 5). These includes, Sallum plateau (U1), Coastal saline depressions (U2), Inland sandy plains (U3), Inland rocky plains (U4), and Shallow wadis (U5). Table (6) showed the numbers and percentages of the families, genera and species that recorded in each of the five geomorphologic units in the study area. The largest percentages were recorded in the inland sandy plains (U3), Inland rocky plains (U4), Coastal saline depressions (U2) and Shallow wadis (U5), respectively. The largest families (Asteraceae, Fabaceae, Brassicaceae, Poaceae, Boraginaceae, Chenopodiaceae, Caryophyllaceae) constituted high percentages (47.49%) of the total species in the study area (Tables, 6 and 7). Plant life forms result from evolved adaptations to climate and other environmental factors (Kassas, 1955). The life-form spectrum of the whole study area (Table 8; Fig. 8) showed that the proportion of therophytes (52.97%) is higher than that of other life forms, while the percentage of chamaephytes and hemicryptophytes (16.89%).
59
Map (5): Location of the five geomorphologic units in the study area. U1=Sallum plateau, U2=Coastal Saline depressions, U3=Inland sandy plains, U4=Inland rocky plains and U5=Shallow wadis.
Table (6): Number and percentage (%) of the families, genera and species recorded in five geomorphologic units in the study area, (N = number of species recorded, U1 = Sallum plateau; U2 = Coastal saline depressions; U3 = Inland sandy plains; U4 = Inland rocky plains and U5 = Shallow wadis U1 N
%
U2 N
%
Families 13 27.66 19 40.43
U3
U4 %
N 35
N
U5 %
N
%
74.47 21 44.68 19 40.43
Total 47
Genera
21 13.64 43 27.92 115 74.68 46 29.87 41 26.62
154
Species
25 11.42 58 26.48 163 74.43 63 28.77 52 23.74
219
60
Table (7): Number of genera and species of the largest families in the five geomorphologic units. for Abbreviation of units, see Table (6).
Geomorphologic units Families
G
U1 SP
G
U2 SP
G
U3 SP
G
SP
G
SP
Asteraceae
4
4
3
4
27
32
8
6
6
Fabaceae
-
-
3
7
13
28
2
1 4 5
5
9
Brassicaceae
-
-
1
1
11
16
3
3
4
4
Poaceae
1
1
4
4
11
13
3
3
4
4
1 1 -
1 5 -
3
3
8
4
5
6
9
2
1 1 3
-
-
4
6
2
2
3
3
75
10 7 16 3
2 8 4 6
4 1 6 3
2 6 4 1
3 1 5 2
Chenopodiaceae
3
4
Boraginaceae
-
-
Caryophyllaceae
1
1
-
-
Total
9
Total of all G ,SP recorded in units
2 1
1 0 2 5
2 2 4 3
3 1 5 8
11 5
U4
U5
The dominance of cryptophytes, therophytes and hemicryptophytes were much less coincides 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 & Kehl, 1985 and Pignatti & Pignatti, 1989). The high contribution of annuals may be related to their short life cycles (sometimes few weeks) that enable them to avoid the arid desert ecosystem of the study area. They also have the ability to set seeds without the need of 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 “ therophytes climate” for the Mediterranean climate where a high percentage (>50% of total species) of therophytes is noteworthy. Raven (1971) pointed out that several Mediterranean floras follow this trend: Cain (1950) in Palestine and Quézel (1978) in North Africa.
Table (8): Spectrum of life-forms of the study area. 61
Life-forms
Abberviations
N0.of species
%
Th Ch He Cr N-Ph P
116 37 37 19 7 3 219
52.97 16.89 16.89 8.68 3.20 1.37 100
Therophytes Chamaephytes Hemicryptophytes Cryptophytes= Geophytes Nano-Phanerophytes Parasites Total number of species rcorded
62
37
37
19
7
3
219
Ch
He
Cr
N-Ph.
P
Tot. 100
1.37
3.20
8.68
16.89
16.89
52.97
%
Th
Ch
He
Cr
Ch
N-Ph.
P N-Ph.
Cr
P
He
63
Fig. (8): Life-forms analysis of the species examined as numbers and percentages of the total species recorded
116
N0. of species
Th
Lifeforms
Th
The distribution of the different life forms in the five geomorphologic landscape units was shown in (Table 9). Clearly, the inland sandy plains and shallow wadis had the highest share of annuals, (67.48%, 61.54%, respectively). El-Ghareeb & Rezk (1989) provided evidence that therophytes acquire dominance in less saline and sandy habitat, whereas cryptophytes and chamaephytes 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 (Table 8). 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 (28.84%) in the shallow wadis and (76.00%, 75.86%, and 74.60%) in the Sallum plateau, Coastal saline depressions, and Inland rocky plains, respectively. They seem to play an important role in the process of sand accumulation and succession of vegetation in the study area. Plants of the latter 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 buds from their buried organs and to replace them when they die. This also has been noted along the Mediterranean coast of Egypt (Batanouny, 1973; Khedr, 1993).
64
3 10 4 5 3 25
Chamaephytes
Hemicryptophytes
Cryptophytes
Nano-phanerophytes
Parasites
Total number of species recorded
N
Therophytes
Life-form
U1
100
-
12.00
20.00
16.00
40.00
12.00
% 7
58
3
4
9
14
21
N
U2
65
100
5.17
6.90
15.51
24.14
36.21
12.07
%
163
-
2
12
19
20
110
N
U3
100
-
1.23
7.36
11.66
12.27
67.48
%
63
-
5
9
13
25
11
N
U4
100
-
7.94
14.29
20.63
39.68
17.46
%
52
-
5
1
7
7
32
N
U5
100
-
9.62
1.92
13.46
13.46
61.54
%
Table (9): Numbers and precentages of the life-forms represented in the geomorphologic landscape units in the study area. For Abbreviation of units, see Table (6).
Species distribution ranges Four of the recorded species were ubiquitous (have a wide ecological range of distribution) and represented in all the five geomorphologic units, e.g., Deverra tortuosa. Thymelaea hirsuta, Haloxylon salicorincum and Anabasis articulata. Ten species were recorded in the units (Peganum harmala, Echinops spinosus, Gymnocarpos decander, Atriplex halimus, Lygeum spartum, Asphodelus ramosus, Asparagus stipularis, Asparagus aphyllus and Carduncellus mareoticus). Sixteen species were recorded in three units (e.g. Periploca angustifolia, Lycium shawii, Salsola imbricata, Salsola tetrandra, Helianthemum kahiricum, Salvia lanigera and Carrichtera annua. Sixty seven species were recorded in two units (e.g. Nitraria retusa, Artemisia judaica, Heliotropium bacciferum, Ononis vaginalis, Suaeda pruinosa, Launaea nudicaulis, Convolvulus arvensis, Citrullus colocynthis, Lotus creticus, Lotus angustissimus, Silene vivianii, Medicago laciniata, Trigonella stellata, Erodium chium, Astragallus schimperi. One hundred and twenty two species or about 55.70% of the total recorded species demonstrated a certain degree of constancy (Table 10). They exclusively recorded in or confined to a certain geomorphologic unit, and do not penetrate elsewhere. Table (10) : Number and perecentages of species and their distribution in the different geomorphologic land scape units of the study area.
No.of species recorded NO. of species One unit Two units Three units Four units Five units Total
122 67 16 10 4 219
% 55.71 30.59 7.31 4.57 1.82 100
In the Sallum plateau, Euphorbia dendroides and Erodium crassifolium were recorded. The former species was 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 66
that confined to the Marmarica district of the Mediterranean coastal land of Egypt (El Hadidi & Fayed, 1978). El Garf (2003) reported that wadi Halazeen (west of Mersa Matruh) supports a dense growth of Euphorbia dendroides. Urgent conservation measures should be taken for this species in its natural habitat. In the coastal saline depression, where halophytic vegetation dominates, Arthrocnemum macrostachyum, Halocnemum strobilaceum, Frankenia hirsuta, Ammophila arenaria and Limoniastrum monopetalum were the dominant. These species comprise the common salt marsh plant communities in the western Mediterranean region of Egypt (Shaltout & 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. One hundred and sixty three species are confined to the inland sandy plains of which 110 are annuals. This landform is known to be the richest among the others. In the inland rocky plains sixty-three species were recorded, one species is threatened, Zilla spinosa sub sp. biparmata. Three species from the inland sand plains and six from the inland rocky plains were recorded. The latter landscape unit favors the growth of certain chasmophytes, e.g. Globularia arabica, and Noaea mucronata. Seven species were common in both landscape units: Heliotropium lasiocarpum, Heliotropium bacciferum, Echiochilon fruticosum, Erucaria microcarpa, Convolvulus arvensis, Convolvulus althaeoides and Gynandriris sisyrinchium. Fifty-two species are confined to the shallow wadis of which 32 were annual. This landform is 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 vegetationaly and floristically rich, and used mainly as rangelands (Kamal, 1988). The phytosociology and vegetation analysis of some these wadis were the subject of El Hadidi & Ayyad (1975), and extended by El-Kady & Sadek (1992) and Kamal & El-Kady (1993). Among the recorded species Retama raetam, Citrullus colocynthis, Anthemis microsperma, Trigonella stellatta, Malva parviflora, Reichardia tingitana, and Cutandia dichotoma, were included. Chorological affinities Results of the total chorological analysis of the surveyed flora presented in Table (11) revealed that (41.55%) of the studied species were 67
monoriginal, of which (20.55%) being native to the Saharo-Arabian phytochoria. Typical Mediterranean ranked second (19.63%), while Sudano-Zambezian and Irano-Turanian phytochorias were very modestly represented. About (53.88%) of the recorded species were biregional or pluriregional, extending their distribution all over the Saharo-Arabian, Sudano-Zambezian, Irano-Turanian, Mediterranean and Euro-Siberian phytochorias. Being part of the Mediterranean region, the Mediterranean phytocoria (uni, bi, and pluri) constituted (57.53%) of the recorded species, whereas the Saharo-Arabian constitutes (36.53%). Thus they form together the major components (94.06%) of the floristic composition in this study. The biregional Mediterranean-Saharo-Arabian, Mediterranean-IranoTuranian, Sahro-Arabian-Irano- Turanian chorotypes constitute the highest values (9.13%, 9.59%, 9.13%), respectively (Table, 12). The results obtained are in agreement with the findings of White (1993), who reported 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. Distribution of the major phytochoria in the five geomorphologic units displayed in Table (12), Fig (9). The decrease in the numbers of the Mediterranean species in the Sallum plateau and coastal saline depressions, and the increase of the Saharo-Arabian species in the Inland rocky plains and Shallow wadis was noticeable. 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 recorded species occurring in the study area, together with their distribution in the different geomorphologic units and chorotypes is given in the appendices.
68
Table (11): Chorological analysis of the species examined as numbers and percentages of the total species recorded. (MED = Mediterranean, SA = SaharoArabian, IT = Irano-Turanian, ES = Euro-Siberian, SZ = SudanoZambezian ).
Phytochoria
Number of species
%
MED
43
19.63
SA
45
20.55
IT
2
0.91
SZ
1
0.46
Total
91
41.55
MED+SA
20
9.13
MED+IT
21
9.59
MED+ES
4
1.83
SA+IT
20
9.13
SA+SZ
11
5.o2
Total
76
34.70
MED+SA+IT
12
5.48
MED+IT+ES
20
9.13
MED+SA+SZ
4
1.83
MED+SA+ES
2
0.91
SA+SZ+IT
4
1.83
Total
42
19.18
Cosm
9
4.11
Pal
1
0.46
Total
10
4.57
Total of all species
219
100
Total of MED
126
57.53
Total of SA
80
36.53
Total of MED+SA
206
94.06
Monoregional
Biregional
Pluriregional
69
Table (12): Distribution (%) of the major phytochorias in the five geomorphologic units in the study area. For Abbreviation of units, see Table (6). Geomorphologic landscape units
U1
U2
U3
U4
U5
Phytochoria Mediterranean
24.00 27.59 16.56 19.05 13.46
Saharo-Arabian
16.00 12.07 22.70 22.22 26.92
Mediterranean + Saharo-Arabian
24.00 10.43
8.59
15.87
9.62
Mediterranean +Irano-Turanian
4.00
8.62
9.20
6.35
11.54
Saharo-Arabian +Irano-Turanian
4.00
6.90
11.66
3.17
11.54
Saharo-Arabian + SudanoZambezian
8.00
6.90
3.07
11.11
5.77
70
0
5
10
15
20
25
30
U1
U2
Units
U3
U4
U5
SA & SZ
SA & IT
MED & IT
SA MED & SA
MED
71
Fig. (9): Distribution of the major Phytochoria in the five geomorphologic units in the study area.
Phytochoria (%)
Mapping of the perennial species The GIS technology revealed that the perennial species of the study area are distributed under four main types namely littoral distribution , inland distribution , scattered distribution and specific distribution. I: Littoral distribution In this type, plant distribution is confined and restrected to the coastal belt of the Meditrranean Sea and the species do not penetrate westward to the inland part. This type could be distinguished into three sub types: a) General littoral distribution along the Mediterranean coast (eg. Zygophyllm album, Lygeum spartum, Asparagus aphyllus and Limoniastrum monopetallum). b) Westren littoral distribution in which the species were confined to the westren part (e.g. Halocnemum strobilaceum, Arthrocnemum macrostachyum, Sporobolus spicatus and Limonium pruinosum). c) Eastern littoral distribution in which the species were confined to the eastern part (e.g. Ononis vaginalis and Pancratium maritimum). II: Inland distribution: in which the species distributed along the foot of El-Diffa platuea; some of them are inhabiting the western part of the study area (e.g. Retama raetam, Euphorbia retusa and Citrullus colocynths). III: Scattered distribution: in which the species distribution recorded wher allover the study area (e.g. Thymelaea hirsuta, Haloxylon sallicorincum, Anabasis articulata, Asphodelus ramosus, Deverra tortuosa, Salsola tetrandra, Gymnocarpos decander, Lycium shawii, Suaeda pruinosa, Atriplex portylacoides, Noaea mucronata). IV- Species with specific distribution: Some other species exhibit specific distribution pattern, where the species were recorded in 1-3 stands scatered in the study area. Some of them are very important (e.g. Euphorbia dendroides which represent the pure Meditrranean element in the study area, Zilla spinosa sub sp. biparmata represent indegenous plant and Artemisia judaica, Urgina maritima, represent the medical plants).
72
General Littoral Distribution
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
Vegetation Analysis of Sallum Area Floristic composition A total of 111 species (36 annuals and 75 perennials) belonging to 92 genera and 34 families of the vascular plants were 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 more than two-thirds (64%) of the recorded species, and represent most of the floristic structure in the Mediterranean North African flora (Quézel, 1978). The largest genera include Astragalus (7), Lotus and Erodium (3 for each), Launaea, Atriplex, Silene, Medicago, Limonium, Asparagus and Asphodelus (2 for each). The most common perennials recorded were Haloxylon salicornicum, Thymelaea hirsuta, Asphodelus ramosus, Anabasis articulata, Atriplex portulacoides, Limoniastrum monopetalum and Salsola tetrandra. Each of these species attains a maximum importance value (IV) of more than 140 (out of 300 for all species in a stand), and a mean of more than 60 (Table, 13). Common but less important perennials were Retama raetam, Deverra tortuosa, Lycium shawii, Arthrocnemum macrostachyum, Halocnemum strobilaceum, Periploca angustifolia and Zygophyllum album. Common annuals include Trigonella stellata, Senecio glaucus, Cotula cinerea, Eremobium aegyptiacum, Arnebia decumbens, Calendula arvensis, Aizoon hispanicum, Schismus barbatus, Erodium laciniatum and Bassia muricata. Classification of vegetation The application of TWINSPAN on the importance values (IV) of the 55 perennial species recorded in 53 sampled stands helped to distinguish five vegetation groups (Table 13, Fig.10). These groups were named after their leading dominant species (those have the highest relative IV) as follows: (A) Haloxylon salicornicum, (B) Haloxylon salicornicumThymelaea hirsuta, (C) Thymelaea hirsuta-Anabasis articulata, (D) Haloxylon salicornicum-Atriplex portulacoides, and (E) Salsola tetrandraLimoniastrum monopetalum. Each of these groups could easily be linked to a habitat type: foot of the Diffa plateau, sand plains, non-saline depressions, saline depressions and the coastal salt marshes, respectively Map (6). 103
Fig. (10): TWINSPAN dendrogram of the 53 studied stands of the Sallum area based on their importance values. A-E are the five separated vegetation groups.
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, inhabited the coastal saline depression was separated on the right side of the dendrogram (Fig. 10), while the left side is still heterogeneous. 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.
104
Table (13): Species composition of the 53 stands in Sallum area, 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. Entries in bold are indicator species in each group. See text for explanation. TWINSPAN group
A
B
C
D
E
Group size
9
8
11
13
12
Total number of perennial species
13
12
14
16
9
Total number of annuals Haloxylon salicornicum Retama raetam Astragalus sieberi Carthamus glaucus Hyoscyamus muticus Lycium shawii Farsetia aegyptiaca Periploca angustifolia Citrullus colocynthis Euphorbia retusa Marrubium alysson Thymelaea hirsuta Deverra tortuosa Lygeum spartaum Globularia arabica Zilla spinoa subsp. biparmata
23
7
9
155 49 4 5 8 17 9 7 7 10 6 5 5 -
78 2 2 16 75 50 1 10 15 15 24 1 1 -
4 36 8 1 1 1 100 2 82 46 1 2 7 3 3 1 -
9 6 1 7 7 15 31 66 65 64 13 15 9 14 8 8
Anabasis articulate Asphodelus ramosus Carduncellus mareoticus Echinops spinosus Gymnocarpos decander Atriplex portulacoides Helianthemum lippii Nitraria retusa Noaea mucronata Verbascum letourneuxii Salsola tetrandra Limoniastrum monopetalum Halocnemum strobilaceum Suaeda proinosa Arthrocnemum macrostachyum Sporobolus spicatus Zygophyllum album Frankenia hirsute Limonium pruinosum
105
94 1 10 4 25 26 26 3 1 64 4 3 2 2 26 1 1 1 1 2 -
Group A. Haloxylon salicornicum The 9 stands of this group were sampled from the foot of the Diffa plateau [Fig, (10), Map, (6)]. On the highly elevated and gravely calcareous soil with moderate moisture content and the least amounts of organic matter and salinity (Table, 14), sand sheets inhabited by Haloxylon salicornicum were found. It was associated with the growth of shrubs of Retama raetam, Lycium shawii, and Farsetia aegyptia, and occupied parts of the drainage channels of the southern parts 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 A combination of Haloxylon salicornicum and Thymelaea hirsuta found on the sand plains with deep loose soil and the lowest levels of moisture content characterized the landscape of this group. It represents a transitional zone between the non-saline and saline depression vegetation groups. This group was characterised 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 pereginus. The most common xerophytic species in the Egyptian Desert, Sinai, and the neighboring arid environments were included in this group (Zohary, 1973; Batanonuny, 1979, Salama & Fayed, 1990, and Abd El-Ghani & Amer, 2003).
106
A-Haloxylon salicornicum. B- Haloxylon salicornicum – Thymelaea hirsuta. C- Thymelaea hirsura – Anabsis articulata. D- Haloxylon salicornicum – Atriplex portulacoides. E- Salsolo tetrandra – Limoniastrum monopetalum.
Map (6): Location map of the Sallum area showing the distribution of the TWINSPAN groups.
Group C. Thymelaea hirsuta-Anabasis articulata This vegetation group dominated the non-saline depressions with soils of the highest pH values and the lowest levels of carbonate content (Table 14). Other physical soil properties were comparable to those of group B. Gymnocarpos decander, Asphodelus ramosus and Astragalus siberii were common perennial , the annual herbes included Centaurea glomerata, Lotus angustissimus, Asphodelus tenuifolius and Hordeum leporinum. Group D. Haloxylon salicornicum-Atriplex portulacoides This group exhibited the largest number of stands (14), 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 107
and clay) (Table 14). Relatively high soil salinity favoured the growth of some salt-tolerant species as Atriplex portulacoides, Salsola tetrandra and Nitraria retusa. The shrub layer was characterised by the growth of Carthamus glaucus, Anabasis articulata, Carduncellus mareoticus and Deverra tortousa. 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 This vegetation predominates the salt marshes with saline soil characterised by Na+, K+ and Mg++. The common associates were three halophytes namely Halocnemum strobilaceum, Salsola tetrandra and Limoniastrum monopetalum (12 stands). Notably, other 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, Brassica tournefortii, Centaurea glomerata, Astragalus hispidulus and Hordeum leporinum. Soil characteristics of the five vegetation groups were summarised in Table 14. Of the measured soil 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. Ordination of stands Figure 11 showed the ordination results of the Detrended Corresponding Analysis (DCA) 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 S.D units along the first axis (eigenvalue= 0.81), expressing the high 108
floristic variations among vegetation groups, and indicating a complete turnover in species composition took place (Hill, 1979). This diagram displayed graphically that group B was transitional in its composition between the other groups. Stands of group E were separated towards 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 S.D was less important. The species-environment correlation (Table 15) 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. From Table 15, 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. We interpreted DCA axis 1 as an altitude-soil salinity gradient. As axis 2 was significantly correlated with total carbonates and altitude, DCA axis 2 was interpreted as an altitude-carbonate gradient
109
Table (14): Mean values and standard deviations (±) of the soil variables in the stands representing the vegetation groups obtained by TWINSPAN in Sallum area. MC = Moisture content, OM = Organic matter, EC = Electric conductivity and Alt = Altitude, * = Differences significant at P < 0.05. Soil variabl e
Mean ± SD
TWINSPAN vegetation groups
Frati o
A
B
C
D
E
Sand %
99.9 ± 0.08
99.7 ± 0.02
99.9 ± 0.04
99.8 ± 0.07
99.8 ± 0.07
99.9 ± 0.1
2.1
Silt %
0.07 ± 0.07
0.01 ± 0.02
0.07 ± 0.03
0.08 ± 0.06
0.1 ± 0.06
0.06 ± 0.09
2.5
Clay %
0.02 ± 0.02
0.01 ± 0.03
0.02 ± 0.01
0.01 ± 0.01
0.02 ± 0.01
0.04 ± 0.03
3.8*
MC %
3.4 ± 4.6
3.16 ± 3.4
2.12 ± 0.09
2.2 ± 1.70
2.5 ± 1.6
6.7 ± 8.3
2.2
OM %
0.2 ± 0.01
0.08 ± 0.09
0.19 ± 0.13
0.2 ± 0.14
0.3 ± 0.14
0.2 ± 0.2
3.9*
CaCO3 %
5.8 ± 2.4
6.9 ± 2.2
5.7 ± 2.30
4.5 ± 1.90
6.0 ± 2.1
5.90 ± 3.1
1.3
pH
9.1 ± 0.03
9.2 ± 0.4
9.2 ± 0.15
9.4 ± 0.20
9.3 ± 0.2
8.70 ± 0.1
7.0*
EC (mS Cm1)
1.1 ± 1.80
0.36 ± 0.03
0.45 ± 0.10
0.41 ± 0.06
0.6 ± 0.2
3.30 ± 3.0
8.9*
Na+(m eq/l)
0.4 ± 0.08
0.04 ± 0.01
0.11 ± 0.08
0.08 ± 0.05
0.2 ±0.15
1.5 ± 1.1
15.7*
K+ (m eq/l)
0.06 ± 0.05
0.03 ± .007
0.04 ± 0.02
0.04 ± 0.01
0.06 ± 0.02
0.12 ± 0.07
8.4*
Mg++(me q/1)
0.01 ± 0.006
0.005 ± 0.009
0.008 ± 0.003
0.008 ± 0.003
0.009 ± 0.004
0.02 ± 0.008
7.3*
Alt (m)
25.6 ± 27.3
62.0 ± 28.2
31.0 ± 21.8
21 ± 15.3
23.1 ± 21.4
2.0 ± 12.7
12.1*
Soil-vegetation-diversity relationships The successive decrease of the eignvalues of the first three CCA axes (Table 15), suggesting a well-structured data set. These eignvalues 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 was not explained by environmental variables (Franklin & 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 intraset correlation of the soil factors with the first three axes of CCA shown in Table 15, it can be noted that CCA axis 1 was correlated to clay, moisture 110
+
content, pH, EC, K , and altitude. This fact becomes more clearly in the biplot (Fig. 12). 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
