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Zeitschrift/Journal: Verhandlungen der Gesellschaft für Ökologie

Jahr/Year: 1996

Band/Volume: 25_1996

Autor(en)/Author(s): Deil Ulrich, Müller-Hohenstein Klaus

Artikel/Article: An outline of the vegetation of Dubai (UAE) 77-95 An outline of the vegetation of Dubai (UAE)

Ulrich Deil & Klaus Müller-Hohenstein*

Synopsis ignorant of the vegetation in the Arabian Peninsula«. After an introduction to the physical environment of The recently published Atlas of the United Arab Emi­ Dubai, the vegetation is described by transects and rates (= UAE) (UAE UNIVERSITY 1993) offers no tables. Plant communities are characterized by their useful information about the vegetation. The survey floristic composition. They are interpreted in the con­ by SATCHELL (1978) about the ecology of the Emi­ text of the saharo-arabian vegetation. Some general rates is in its geobotanical part based on the brief pa­ problems in the application of the phytosociological per of VESEY-FITZGERALD (1957). approach to desert vegetation are discussed. The first aim of this contribution is to give a com­ The Emirates have a hot desert climate. The com­ prehensive information about the most important ve­ bination of a tropical temperature regime and winter getation types and land units of Dubai. We concentrate rain results in a mixture of holarctic and paleotropic on the coastal region and the foreland of the Musandam elements. The endemic species belong to the omano- Mountains. These data are based on field trips by MÜL­ makranian chorotype. LER-HOHENSTEIN in 1986 and by DEIL in 1987. The pattern of the plant communities is ruled by Secondly, the vegetation of Dubai will be com­ the relief. The coastal vegetation complex is characte­ pared with other regions of the Old Wold desert belt rized by Limonium stocksii and Zygophyllum qata- and interpreted in a wider geographical context. This rense. On the dunes grows the Cornulaco monacan- comparison is based on a personel knowledge of the thae-Sphaerocometum aucheri, in silty depressions desert vegetation in the Maghreb countries and in the Halopeplidetum perfoliatae. The inland dune ve­ North Yemen and on the available literature. getation is dominated by Rhanterium epapposum. The third topic are chorological aspects. Southern The original Prosopis cineraria- woodlands there have Arabia is the transition zone from the Holarctic to the been nearly everywhere destroyed and are replaced Paleotropical Kingdom, from extratropical to tropical by the Leptadenio-Rhynchosietum schimperi. In the climate. How is this situation reflected by the plant dune valleys we find the Helianthemum lippii-Fago- communities in Dubai and do the different life forms nia ovalifolia- community. The ephemeral Chrozo- react in a different way? FREITAG (1991) demon­ phora sabulosa-c ommunity develops on the inland strated, that even the halophytes, growing quite inde­ dunes, the Frankenio-Zygophylletum simplicis on sal­ pendently from the precipitation regime and there­ ty sand. In the stony desert, the Pseudogaillonio hy- fore often regarded as »azonak, show a clear geo­ menostephanae-Euphorbietum laricae colonizes rock graphical pattern around the Arabian peninsula, outcrops. The Saccharo griffithii-Nerietum masca- mostly ruled by temperatures. tense is the wadi vegetation type of deep incised canyons. Finally a syntaxonomic survey is given. 2 Methodological and synsystematic problems Saharo-Arabian vegetation, chorology, phytosociology, desert ecology Under arid conditions and in extreme habitats like saline depressions, plant communities are often com­ posed of very few species and there exist also mono- 1 Introduction specific vegetation units like the Halopeplidetum per­ foliatae. Nevertheless, they can be associations in the There has been a good progress in the floristic know­ sense of the phytosociological approach of BRAUN- ledge of the Southeastern parts of the Arabian penin­ BLANQUET (1964). In other cases, they are named sula by the flora of MANDAVILLE (1990), the Emi­ and classified according to the dominant species and rate flora of WESTERN (1989) and the more popular are fazies of associations sensu strictu. If we have a introduction to the nature of Dubai by JONGBLOED look at the geobotanical literature of the Middle East, (1987). But detailed studies about the vegetation of there are some authors, which refer to the Braun- this part of Arabia are still missing. The statement of Blanquet approach. But indeed, they use only the ZOHARY (1973) is still up-to-date: »We are especially values proposed by BRAUN-BLANQUET to estimate the cover-abundance of the species. Their vegetation * Dedicated to Prof. Dr. Reinhard Bornkamm on the units are based on dominant species, not on the fide­ occasion of his 65th birthday. lity of the taxa in a big data set. The result is an infla- Fig. 1 Climatic Diagram of Dubai

T| = mean monthly maximum temperatures T 2 = mean monthly minimum temperatures P = mean monthly precipitation H| = mean monthly maximum of the air humidity H-> = mean monthly minimum of the air humidity

27.1°C = mean annual temperature (81°F) 83.2mm = mean annual sum-total of precipitation (3.27”) 47.3°C = absolute maximum temperature (117°F) 7.7° C = absolute minimum temperature (46°F) 231.2mm= highest amount of precipitation per year (9.1") 22.8mm = lowest amount of precipitation per year(0.89") Period of observation 1973 - 1984

Fig. 2 The natural landscapes of Dubai tion of »communities«, often documented only by a are two major problems in such studies: First, the cri­ single relevé or by a constancy column, in some cases teria of botanists for environmental homogeneity are even without any tables. These communities are not different. Secondly, we have to deal with taxonomic arranged in an hierarchical system, which would be and nomenclatural problems. Older studies often use the expression of the gradual ecological value of the collective taxa, for example in the genera Calligo- species. num , Fagonia, Stipagrostis, Helianthemum, Limo- The decision, whether the communities are a typus nium, Cyperus (Section Arenarii ) or Zygophyllum. or not, could be taken by comparative tables, like it For Zygophyllum , EL-HADIDI (1977) has clearly has been done by BORNKAMM & KEHL (1990) in shown, that a finer taxonomic treatment of an euryoe- their survey of the Western desert of Egypt. But there cious and widely distributed taxon ends up with ste- Fig-3 Phytogeographical and climatical frontiers in Arabia1 (adopted from MÜLLER-HOHENSTEIN 1988, see further references there)

1 On the left: Borderlines between the Holarctic and the Paleotropical Kingdom after DIELS 1908 (dotted line), AL HUBAISHI & MÜLLER-HOHENSTEIN 1984 (continuous) and KÜRSCHNER 1986a (intermittent)

On the right: Borderlines between subtropical and tropical climatic zones after TROLL & PAFFEN 1965 (dotted line), VON WISSMANN 1962 (continuous) and CREUTZBURG & HABBE 1964 (intermittent)

noecious, regional vicariants: Zygophyllum qataren- wing concept: If the classification and syntaxonomic se, one of the most common species in the coastal re­ value of a unit is clear, the association is named ac­ gions of Dubai, Qatar and Northern Oman is replaced cording to the rules of the plant sociological system further to the north by Z. migahidii , to the southwest (BARKMAN et al. 1986). In other cases, the term by Z hamiense and to the west by Z. mandavillii. In »plant community« is used for a rankless vegetation other cases, different names are synonymous. unit. We use the cover-abundance values of BRAUN- Another problem is, that there exist three synta- BLANQUET (1964), sociability notes are not given. xonomical systems of quite different origin: The sy­ In the tables, the abbreviation CS stands for character stem of QUEZEL (1965) gives a survey of the vegeta­ species, DS for differential species. The nomenclature tion of the Western and Central Sahara. His system is here follows MANDAVILLE (1990), BATANOUNY inductive. He started from the association level to the (1981) and COPE (1985). The herbarium specimen higher syntaxa. In the Near and Middle East, the sy­ are stored at Bayreuth. stem of ZOHARY (1973) is widely accepted. His sys­ Another problem is, that the vegetation cover tem is deductive, he started from the classes. Both can be classified at different spatial scales and several books do not offer comparative tables and do not pay levels of homogeneity: Three common levels are the much attention to the syntaxa of medium rank (or­ synusium, the community and the vegetation com­ ders and alliances). LEONARD (1993) has shown the plex. Here we use the community and the vegetation unsharp definition of the »communities« by ZOHARY complex level. A still unsolved problem is the stra­ (1963): Within 24 units, Artemisia herba-alba is used tum built by ephemeral species: Should we handle as the naming dominant species, but Artemisia her- them as a synusium in a pluristratified community, as ba-alba s.str. does not occur at all in Southern Iran. a chronocoenose or as an independent unit? We will The third proposal is the classification of the vege­ discuss this by some examples in chapter 5 (see also tation of Eastern Africa by KNAPP (1968). It is very the discussions in BAIERLE 1993 to the wadi com­ useful for the tropical parts of Arabia, but this con­ munities in Southwest Jordan). tribution was published in a quite unknown series and therefore not taken into account by ZOHARY (1973). 3 Physical conditions of the study area The aim of this contribution is not a syntaxono- mical one. We want to characterize the vegetation of A detailed description of the environmental condition a small territory. But we also want to interpret our of the UAE is given by SATCHELL (1978) and some data in a wider context. Therefore we use the follo­ information can also be drawn from the recently Fig. 4 Climatic conditions of coastal areas in southern Arabia published Atlas (UAE UNIVERSITY 1993). We con­ Arabian Sea and th e ^ u lf of Oman are prevented centrate on those data, which are important for an from reaching the Arabian Gulf by the Oman Moun­ understanding of the spatial pattern of the flora and tains, which receive considerably higher precipita­ vegetation of Dubai. tions (BABIKIR 1985). Rainfall pattern is very va­ riable, both in time and space. Air humidity is high at night throughout the year (see Fig. 1), mean rela­ 3.1 Climate tive humidity is about 60 % in the coastal parts (UAE UNIVERSITY 1993). Water supply for plants is regu­ Dubai has a hot desert climate. The potential évapo­ larly improved by dew at night and sometimes by fog transpiration for the Emirates is more than 1000 mm in the late afternoon. per year (up to 3.4 mm/h in extreme situations). Mean annual temperature for Dubai is 27.1°C, Mean annual rainfall is less than 100 mm per year. the coastal parts of Eastern and Southern Arabia are As can be seen from the climatic diagram (Fig. 1), frostfree. According to the temperatures and air hu­ rainfall concentrates on late winter and early spring. midity, the Emirates belong to the tropical climates, Not even at this time, at the ‘humid season’, month­ according to the genesis and distribution of rainfall to ly precipitation balances the potential évapotranspi­ the extratropical ones. This unique mixture (tropical ration. The climate is arid throughout the year. The and extratropical) of climatic elements has created a winter rain maximum is of the mediterranean type special environment for plants and resulted in ende­ and origin. Erratic thunderstorms in summer are mic plant species in this part of Arabia and Southern caused by the northernmost influences of the Indian Iran as well as in a particular mixture of holarctic and summer monsoon, but most of the winds from the paleotropic phytochoria (see chapter 4). dense.microphyllous shrubs: C'ornulaca monacantha. Sphaerocoma aucheri. Heliotropium kotschyi lower succulent shrub: Halopeplis peifoliata E l sand and gravel perennial bushy grasses and leafless shrubs:Panicum turgidum,Croialaria pérsica, Taverniera spanea saline silty sand halophylic annuals:Frankenia pulverulenta. ZygophyUum simplex. Suaeda aegyptiaca annuals, p.p.salt tolerant:Arnebia hispidissima. Reichardia tingitana, Senecio glaucusssp, coronopifolius E l dune sand

Fig. 5 The coastal dune and sabcha ecosystem

3.2 Relief and substrate EC value is 0.7 mS/cm, a concentration, that already inhibits the growth of salt sensitive plants. The silty Except for higher precipitation and moderate tempe­ and haliferous sabkha soils belong to the solonchaks ratures in the mountainous area, climatic conditions or salorthids. Here gypsum crusts develop occasional­ are quite uniform in the Emirates. The great variety ly and EC values can reach 70 mS/cm in the surface of ecotopes is created by different soil types and relief horizon. The vegetation of the coastal or salt desert, features. Both factors influence water absorption and identical to the white dune and sabkha ecosystem by storage: Sandy soils show a less intensive evaporation other authors (SATCHELL 1978, BABIKIR 1984), will and higher infiltration rate than loamy or silty soils; be described in chapter 5.1 and by transect I (Fig. 5, depressions and floodplains gain run-on water from Tab. 1 and 2). steep slopes; surface layers of deep soil deposits may The inland dune system:At a distance of 10 to comprise a permanent water source for deeply roo­ 15 km from the coastline, the dunes become higher. ting perennial plants. The content of organic matter They form longitudinal dune ridges of eolian red sand in the soils is mostly less than 0.5 %. Plant growth is (torripsamments) and are separated by interdune cor­ in first line restricted by water-holding capacity and ridors and gravel plains. The latter consist of well salt content, not by nutrients. rounded and usually darker remnants of the debris of The plant species distribution and the pattern of Quarternary sediments. Phytogenetic mounds, which the plant communities clearly correlate with geomor­ develop on the lee side of tussock grasses or dwarf phology, because water availability is strictly ruled by shrubs, can be observed quite regularly in the dune the relief. BATANOUNY (1981) therefore introduced valleys and on the gravel plains. No drainage system the term phyto-eco-geomorphological units when dis­ has developed there, the numerous depressions act as cussing the vegetation pattern of Qatar. The large va­ catchments. Further inland huge mobile barchans riety of habitats in Dubai, as it can be seen from the and stellate dunes follow, which reach heights of more schematic transect in Fig. 2, is also expressed by local than 50 meters. This landscape unit includes the Red topographical terms such as Jiri and Sabkha (depres­ sands of the desert foreland sensu SATCHELL (1978). sion), Rodah (dune valley), Hazm (terrace), Jabal Its vegetation, the Red Sand associations sensu (mountain slope), Hassa (gravel plain), Erg and Bark- VESEY-FITZGERALD (1957), will be described in han (dunes). chapter 5.2 and by transect II (Fig. 6 and Tab. 3). From West to East, from the Arabian Gulf coast The stony desert: The outset of the Musandam to the Musandam Mountains, we can distinguish the Mountains is indicated by scattered rock outcrops, following geomorphological units: which consist mainly of dolomitic limestones from The coastal desert:The only natural port is the the Upper Cretaceous and Lower Jurassic. A wadi sys­ creek at Dubai City. The coast itself is fringed by tem, separating the dune fields from the mountains, white dunes, which overlay low beach ridges consi­ follows a tectonic line. The transition from this allu­ sting of coral and shell fragments. Sabkhas are inter­ vial plain to the mountains is formed by pediments calated in the coastal dune fields. In the coastal with a thin gravel layer (torrifluvent). The vegetation dunes, which contain calcareous material, the average of the stony desert is described in chapter 5.3 and is Prosopis -Lycium- community Leptadenio - Rhynchosietum scliimperi Helianthemum lippii- Scattered relict forests on lower, partly plant-fixed dunes Fagonia ovalifolia - community on fixed high dunes in dune valleys with stony surface layer

with Prosopis cineraria (tree) Lycium shawii (spiny shrub) Ephedra foliata (climber)

high leafless shrubs: Leptadema pyrotechmca .Calligonum comosum y perennial bushy grasses:Panicum turgidum,Pennisetum divisum ' ■ ■ □ sand perennial tufted sedge: Cyperus aucheri EZ3 sand and gravel weak tufted grasses: Stipagrostis plumosa, Arisrida adscensioms.Coelachyrum piercei stout shrubs and herbs: Rhanterium epapposum. Rhynchosia schimperi, Heliotropium digynum. Tribulus arabicus, Moitkiopsis ciliaia, Ceniaurea pseudosinaica dwarf shrubs with trufTels: Helianthemum lippii procumbent herb: Fagonia ovalifolia short-lived annuals: Silene villosa.Eremobium aegyptiacum, Neurada procumbens

Fig. 6 The inland dune ecosystem illustrated by transect III, the plant community on analyse the flora as a whole, the Emirates show a bar rock by Tab. 4. The vegetation of the Musandam clear majority of saharo-arabian elements. This is due Mountains, which are rising steeply from the plains, mainly to the numerous therophytes. A more detailed is not discussed here, because we have only insuffi­ analysis was carried out by KÜRSCHNER (1986b), cient information about this relief unit form the terri­ who compared the chorological spectra of the Acacia- tory of Dubai. Prosopis-c ommunity in Mascat separately for each The Wadi systems: The wadi systems are stratum: The result is, that in each layer different phyto-eco-geomorphological units of their own. Some chorotypes are predominant. The tree species are of remarks on this vegetation type are given in chapter the nubo-sindian type, the higher shrubs of the saha­ 5.4 and by Tab. 5.4 ro-arabian type, the therophytes are a mixture of both geo-elements. A precise information can also be gained by com­ 4. The phytogeographic position of Dubai paring the chorospectra of communities in the same environment, as it has been done by MÜLLER-HO­ The flora of the UAE is quite heterogenous in the HENSTEIN (1988) for the dune-communities of Du­ chorological sense due to the fact, that two principal bai and Yemen. The comparison of a single habitat floristic frontiers are meeting there (Fig. 3): a sou­ type shows clearer than a comparison of the whole thern, subtropical flora of paleotropic origin (nubo- flora of both territories the shifting from tropical ele­ sindian elements) and a northern, extratropical flora ments in Yemen to extratropical ones in Dubai. of holarctic origin (saharo-arabian elements). The cli­ Dubai belongs to the Northern Oman center of matic background of this situation is the transition endemism in Arabia (MILLER & NYBERG 1991). It from subtropical summer rain (monsoon type) to ex­ has very strong links to Southern Iran and Afghani­ tratropical winter rain (mediterranean type). This is stan. The coastal lowlands and foothills bordering the illustrated by the climatic graphs of coastal stations in Strait of Hormuz contain a large number of species Southern Arabia (compare especially the climato- that exist only in this part of the world. KÜRSCHNER grams of Wadi Zabid and Sharjah, Fig. 4). The ther­ (1986a) has underlined this by separating an eastern mal conditions in Dubai are tropical, like in the subprovince from the nubo-sindian region, the oma- Yemeni Tihama. no-makranian region. These elements (for example The phytogeographical division of Southern Ara­ Nerium mascatense, Dyerophytum indicum, Saccha- bia has been discussed by many authors (MANDA- rum griffithii, Cometes surattensis, Limonium stock- VILLE 1984, ZOHARY 1973, KURSCHNER 1986a, sii, Sphaerocoma aucheri , Jaubertia aucheri, Pseudo- MULLER-HOHENSTEIN 1988 and others), a synthe­ gaillonia hymenostephana, Euphorbia larica, Proso­ sis is given by WHITE & LEONARD (1991). If we pis cineraria ) play an important role in the characte- umbrella-shaped treesAcacia tortilis trees at wadi marginsProsopis cineraria V high shrubs Euphorbia larica Ziziphus spina-christi Lycium shawii Ficus salicifolia Hammada salicornica shrubs at wadi marginsNerium mascatense Aerva javanica Rhazya stricta A low shrubs Jaubertia aucheri Calotropis procera Pseudogaillonia hymenostephana y shrubs in runnels Ochradenus aucheri '$■ perennial grasses Cymbopogon commutatus Physorrhynchus chamaerapistrum V annuals as Arnebia hispidissima shrubs on gravel plains Cassia italica Sclerocephalus arabicus Tephrosia apollinea Cometes surattensis Pulicaria glutinosa Piantago ciliata Hammada salicornica Rumex vesicarius f perennial grasses Saccharum griffithii Aristida abnormis Juncus acutus Y annuals as Morettia parviflora Tribulus arabicus

Fig. 7 Ecotope pattern and vegetation structure of rock outcrops and gravel plains. rization of the plant communities described here (see landscape unit has been named the ‘salt desert’ by chapter 5). other authors. It is identical with the coastal salt- The late Tertiary migration road to the Horn of bush-associations sensu VESEY-FITZGERALD (1957). Africa is still reflected in the distribution pattern of Plants growing there can tolerate salt, some of them some genera like Ochradenus, Taverniera and Pulica­ are even obligate halophytes like the representatives ria (LEONARD 1988/1989). In recent geologicial of the families Chenopodiaceae, Frankeniaceae and times (still during the Pleistocene period), a low sea Plumbaginaceae. level brought a drying up of most parts of the Arabian This coastal ecosystem has been destroyed nearly Gulf and allowed a free migration of terrestrial orga­ everywhere in Dubai by urbanization, but between nisms (MANDAVILLE 1984). The present conditions Jabal Ali and Jumairah it could still be studied in have prevailed for the last five to six thousand years 1987. All relevés in Tab. 1 and 2 have been taken BEUG (1971).5 there on 15.3.1987. The relevés might be already hi­ storical, because the dunes between Dubai City and Jabal Ali are one of the most important development 5 The landscape units and their vegetation axes (see plate 95 in the UAE Atlas). cover A universal characteristic feature of littoral salt- marshes and dunes is zonation (ZAHRAN 1977). The 5.1 The coastal ecosystem vegetation sampling was carried out along a transect from the coast to the landward side. The relevés in A mosaic of flat white sand dunes and silty depressions Tab. 1 are arranged in this way. A scheme of the zo­ (sabkhas) formerly covered the Arabian Gulf coast. In nation is also given by Fig. 5. both habitats (coastal dunes and sabkhas), salt has a The coastal ecosystem as a whole is characte­ considerable influence on plant life. Therefore this rized by two dwarf shrubs, which give the name to Tab. 1 Limonium stocksii-Zygophyllum qatarense vegetation complex (Transect I in the coastal ecosystem)

Releve N°.

CS of the coastal vegetation complex and PS of omano-makranian variants Limonium stocksii 2 2 3 3 2 2 2 Zygophyllum qatarense + 1 + 1 + 1 2 2 2 1 CS Sphaerocometum aucheri and PS of subassociations Sphaerocoma aucheri + 1 2 2 1 2 Cyperus arenarius 1 + 2 2 Halopyrum mucronatum 1 Aeluropus lagopoides Lotus garcinii + + Crotalaria pérsica + + + + Taverniera spartea 1 2 Indigofera intricata + 1 CS of Halopeplidetum perfoliatae Halopeplis perfoliata .... 1 1 CS Salsolo-Suaedetalia and Halopyro-Sporoboletea Cornulaca monacantha 1 1 2 2 1 1 1 1 Suaeda fruticosa Suaeda aegyptiaca Salsola imbricata 1 Salsola nitraria 1 Heliotropium kotschyi 1111 Atriplex leucoclada 1 1 Sporobolus arabicus Cistanche phelypaea Senecio glaucuscoronopif. Companions Panicum turgidum + + Moltkiopsis ciliata 1 + Launaea mucronata 1 + Launaea capitata Launaea nudicaulis Arnebia hispidissima 2 2 Helianthemum lippii 1 1

Further rare species: in 4: Coelachyrum pierceiv, in 7: Cyperus aff. conglomeratus +; in 12: Halocnemum strobilaceum 1; in 19: Prosopis cineraria (juvenile) +. this vegetation complex: The mound forming Limonium in the plant communities of the Arabian Gulf coast, stocksii and the succulent Zygophyllum qatarense. from Qatar to the UAE and also in the Mascat area in Both species are associated to each other from Qatar Oman. It abounds in shallow depressions with silty- (BATANOUNY 1981, BATANOUNY & TURKI 1983) loamy soils and on the flat coastal dunes. In the in­ to the UAE (see here) and further to Northern Oman land of the UAE it is less common. The germination (BATANOUNY & ISMAIL 1985, KÜRSCHNER 1986b). of Zygophyllum qatarense is inhibited by high tempe­ Limonium stocksii (pp. L. axillare of older publica­ ratures and high salt content (ISMAIL 1990, ISMAIL tions) is a salt-secreting halophyte of omano-makra­ & EL-GHAZALY 1990). It takes place in winter and nian distribution. It colonizes the flat coastal dunes spring, when salts are temporarily washed out from and is also fringing the coastal and inland sabkhas, the topsoil. not inundated by sea water. It is a very effective Within the Limonium-Zygophyllum-complex , we sandbinder. Zygophyllum qatarense (pp. Z. hamiense can distinguish four vegetation units and habitat types, of some authors) is one of the most common species which will be discussed separately: 1 The seaward dunes (Tab. 1, rel. 1-9) are colo­ Sphaerocoma auc/îen-association sensu ZOHARY nized by Sphaerocoma aucheri and Cornulaca mona- (1963), which is a mosaic of several vegetation units. cantha. They are differentiated from the landward The edaphic conditions and the position in the micro­ dunes by Halopyrum mucronatum, Atriplex leucocla- relief of the dunes of the Lotus garcinii-Cyperus con- da and Suaeda aegyptiaca. glomeratus- association (KÜRSCHNER 1986b) is very 2 The landward dunes (Tab. 1, rel. 15-20) are also similar to the subass. typicum, but in Dubai some dominated by Sphaerocoma and Cornulaca. On more species of omano-makranian distribution occur these dunes, away from the influence of sea spray, in this community type ( Crotalaria persica, Taver­ appear Lotus garcinii, Crotalaria persica, Taverniera niera spartea, Indigofera intricata). If more observati­ spartea and Indigofera intricata and some species of ons were available from southern Iran, this subasso­ the inland dune system like Panicum turgidum. ciation might become the rank of an association with­ 3. The salty depressions (Tab. 1, rel. 10-14), tem­ in an alliance, characterized by Sphaerocoma porarily inundated at high spring tide, are characte­ aucheri. Character species of syntaxa of higher rank rized by Halopeplis perfoliata. (class and order) are Cornulaca monacantha, Suaeda 4. An ephemeral salt tolerating plant community, spp., Salsoia spp., Heliotropium kotschyi , Sporobolus the Frankenio-Zygophylletum simplicis, grows on flat arabicus , Atriplex leucoclada and others. These sandy overlays in the depressions (Tab. 2). species are mentioned by KNAPP (1968) as Salsolo- Suaedetalia- and Halopyro-Sporoboletea- CS, by ZO­ C ornulaco monacanthae-Sphaerocometum au­HARY (1973) as Suaedetea fruticosae deserta- CS. cheri ass. nov. These syntaxa have to be described more precisely in Tab. 1, rel. 1-9 and 15-20 the future. For the moment, the Cornulaco-Sphaero- cometum aucheri is included in the Salsolo-Suaede- KÜRSCHNER (1986b) was the first who studied talia (Halopepli-Suaedetea ). more precisely the ecology of Sphaerocoma aucheri. In the Estuary of the Qurm Nature reserve near Mas­ Halopeplidetum perfoliatae ass. nov. ex KAS­ kat this species colonizes, like in Dubai, the coastal SAS 1957 white sand dunes, which are calcareous and of mari­ Tab. 1, rel. 10-14 ne origin. Sphaerocoma ranges, always on coastal dunes, from Bahrain, the UAE and Northern Oman Halopeplis perfoliata is a semi-woody succulent to Balutschistan. In the normal form Subass. typi- shrub. It forms monospecific stands or dominates the cum (Tab. 2, rel. 15-20, type relevé N°. 19), the vegetation in depressions with salorthids in the sou­ omano-makranian endemics Crotalaria persica, Ta­ thern part of the Arabian-Persian Gulf, along the Gulf verniera spartea , the sokotro-makranian Indigofera of Oman and on both coastlines of the Red Sea (for intricata and the eastafrican-makranian Lotus garcinii the distribution see FREITAG 1991, for edaphic con­ are associated with Sphaerocoma. A similar species ditions see KASSAS 1957, KÜRSCHNER 1986b and composition was noted by KÜRSCHNER (1986b) YOUNES et al. 1983). This hygrohalophyte with C3 near Mascat: In small wind protected pockets, he ob­ photosynthetic pathway (FREY et al. 1984) germi­ served a Lotus garcinii-Cyperus conglomeratus-com- nates after rainfall, when salt content is low munity with Heliotropium kotschyi and Suaeda fruti- (MAHMOUD et al. 1983). cosa. Synsystematics: The Halopeplidetum perfolia­ On the seaward side of mobile embryonic dunes, tae is mentioned very often, but has never been pu­ Halopyrum mucronatum is stabilizing the sand. Ha­ blished validly. Most publications do not give single lopyrum stands have been described as communities relevés, the syntaxon is not included into higher syn­ by KASSAS & ZAHRAN (1967), BATANOUNY (1981), taxa. The validation is made here by selecting a re­ BATANOUNY & TURKI (1983), BATANOUNY & IS­ levé from KASSAS (1957), who gives a table of a Ha­ MAIL (1985) and KÜRSCHNER (1986b). In our data lopeplidetum from the Red Sea coast in Sudan. (Tab. 2), this différenciation can also be seen, but this Lectotypus rel. 11 from KASSAS (1957): unit is treated here as a subassociation, because Ha­ Halopeplis perfoliata 2.2 Suaeda fruticosa +. 1 lopyrum is transgressive from its main hygrohaline Arthrocnemum glaucum +.3Aeluropus lagopoides +.2 habitat. The Subass. halopyretosum mucronati The Halopeplidetum has been recorded from the (Tab. 1, rel. 3 -9 , type relevé N°. 6) is more influen­ following regions: Southern Egypt (KASSAS & ZAH­ ced by the sea spray. At the coastline itself (rel. 1 -2), RAN 1967), Sudan (KASSAS 1957), Eritrea (HEM­ an unusual form of Suaeda fruticosa formes a facies MING 1961), Saudi Arabia around Jeddah (VESEY- of its own. FITZGERALD 1955, MAHMOUD et al. 1982, YOU­ Synsystematics: The Cornulaco-Sphaerocome- NES et al. 1983, FREY et al. 1984), the northern Ti- tum includes the Sphaerocoma-d^soc\dX\on sensu hamah in the Asir foreland (KÖNIG 1987), around KÜRSCHNER (1986b), but not the Euphorbia larica- Aden (AL-GIFRI, pers. comm.), the Mascat area in Tab. 2 phyllum simplex is missing in the northern Sahara Frankenio-Zygophylletum simplicis and the mediterranean area. It grows in the central parts and on the southern fringes of the Old World Releve N°. 1 2 3 4 5 6 7 deserts from Senegal to Punjab. Where both species overlap, for example in the central Sahara, in the Si­ CS Frankenio-ZvaoDhvlletum nai, in Qatar and in the UAE, they are associated and Frankenia pulverulenta 2 1 2 2 2 2 V characterize an ephemeral, salt tolerant community. Zygophyllum simplex 1 1 2 2 2 2 1 In Dubai, they have been noted in coastal depressi­ Cyperus aff. tanganyicanus 1 1 1 1 1 2 2 ons between Jabal Ali and Jumairah. The releves CS Cutandietea have been taken on 15.3.87 in the coastal vegetation Oligomeris subulata + 1 1 1 1 1 complex (Fig. 5). Within the Halopeplidetum perfo­ Arnebia hispidissima 1 2 2 2 1 liatae -, the shortliving Frankenio-Zygophylletum Hippocrepis bicontorta + + covers after rainfall flat sandy overlays of the silty de­ Seedlinas of Derennials pressions. Further associated species are the seedlings Zygophyllum qatarense 1 1 + + of the surrounding perennial vegetation and annuals Suaeda aegyptiaca 1 1 1 + 1 1 of the sandy dunes like Arnebia hispidissima. The ta­ Helianthemum lippii + 1 1 + xonomic position of an annual Cyperus, which has Salsola nitraria + + + been found only in this community, is still unclear. It Lotus garcinii + + 2 looks very similar to C. tanganyicanus, endemic in Sphaerocoma aucheri + + Tanzania. Synsystematics: In other studies, the salt tole­ Further rare species: rant ephemeral flora has been treated as an element in 1: Sporobolus arabicus +; of the perennial halophytic communities, for example in 3: Hemiaria hemistemon +, Atriplex leucoclada +; by ZOHARY (1973) within the Suaedetea fruticosae in 6: Ifloga spicata +, Dichanthium foveolatum +; deserta or as a differential species of subassociations, in 7: Limonium stocksii +, Heliotropium kotschyi 1. for example by QUEZEL (1965) in the Salsolo siebe- ri-Zygophylletum cornuti frankenietosum pulveru­ lentae or by BORNKAMM & KEHL (1990) in the Zy- Northern Oman (BATANOUNY & ISMAIL 1985, gophyllo coccinei-Schouwietum thebaicae zygophyl- KÜRSCHNER 1986b), UAE (this contribution) and letosum simplicis. Because the annuals are submit­ Qatar (BATANOUNY & TURKI 1983, BABIKIR 1984). ted exclusively to the edaphic conditions of the top Within this area, we can distinguish several geogra­ soil (independent from the water content in the de­ phical races, characterized by vicarious Limonium pressions, lower salt concentration in the sandy layer and Zygophyllum species. In the omano-makranian after rainfall etc.), this unit can enter several peren­ race occur Zygophyllum qatarense and Limonium nial halophyte communities. It can also grow inde­ stocksii. pendently from perennial vegetation (both character The Halopeplidetum is up to now the only asso­ species enter silinated, abandonned fields). There­ ciation of the Halopeplidetalia perfoliatae Knapp fore, it must be treated as an independent plant 1968 and belongs to the Halopeplidi-Suaedetea community, which may also be a temporal therophy- Knapp 1968, a class mostly synonymous with the tic synusium or chronocoenose within perennial ve­ Suaedetea fruticosae deserta Zohary 1973. getation types. The Frankenio-Zygophylletum can be interpreted Frankenio pulverulentae-Zygophylletum simpli­as the southernmost outpost of the class Frankenietea cis ass. nov. pulverulentae. From the character species of higher Tab. 2, type relevé N°. 2 rank (see the revision of the class by BRULLO 1988), only Frankenia pulverulenta, Sphenopus divaricatus In the central parts of the Sahara and in southern and Spergularia marina go to southern Arabia. Des- Arabia, the distribution of two salt tolerant thero- mazeria spp., Parapholis spp. and other character phytes is overlapping: Frankenia pulverulenta and Zy­ species are restricted to the extra-tropical parts of gophyllum simplex. The first one is to be found from Arabia. If more observations of those short-lived com­ the western Sahara throughout the mediterranean munities were available, the delimination of a south- area to Arabia and in the Indian deserts, the synan- saharo-sindian alliance (Zygophyllion simplicis all. thropic area has been expanded to South Africa, Aus­ nov. prov.) would become more clear. tralia and to mediterranean region of the Neotropis. In the settlements of the UAE, a subnitrophilous The species is almost everywhere restricted to win- association of the Frankenietea has been observed, terrain climate (JÄGER 1992). It is a characteristic the Cressetum creticae Brullo & Furnari 79. Detailed species of the class Frankenietea pulverulentae. Zygo- observations are missing. 5.2 The inland dune ecosystem Releve N°. 1 2 3 4 5 6 7 8 9 1 1 1 1 1 Most parts of the territory of Dubai are covered by 0 1 2 3 4 the inland dune ecosystem, the sandy desert. From Dubai City to Tawi al Hibab we find parallel dunes CS of the Leotadenio-Rhvnchosietum schimperi with intermittent dune valleys and between Tawi al Rhynchosia schimperi ..++++...... Hibab and Wadi Yudayyah irregular higher dunes. Leptadenia pyrotechnica 1 + . . + 1 1 1 1 ...... The low dunes are more or less consolidated and Calligonum comosum + 2 + .+ 1 1 1 1 1 1 . . . . consist of white, calcareous sand of marine origin, Tribulus arabicus 1121+ + + + + + +. . . the high mobile dunes are composed of red silicate Coelachyrum piercei 11111 +...... sand of terrestrial origin. Within this area, habitat va­ PsammoDhilous shrubs of unknow svntaxonomic rank riability is evoked by different grain size and mobility Heliotropium digynum 1 2 + 1 . + ...... of the sand, by the amount of run-on water in the Dipterygium glaucum 1 + + . . 1 . . 1 ...... dune valleys and by grazing intensity. Crotalaria aegyptiaca . . 1 + . ... + ... + . The sandy desert ecosystem has been studied clo­ Polycarpaea repens .. + . . + 1+ . + .+ .. ser in the area around Nakhalai Palace: Some plots CS of Hammadetea and Acacietea (incl. Acacio-Panicion) there are sheltered from grazing. Fig. 6 illustrates life Rhanterium epapposum . . + .1122122121 forms and structure of this vegetation complex. The Stipagrostis plumosa + 1 1 1 ...... 1111 dwarf shrub Rhanterium epapposum is a common Lycium shawii + ... + .+ + ...... grazing plant on lower sand dunes and in dune val­ Ephedra foliata + ...... + ...... leys, characterizing the inland dune system. The spe­ Panicum turgidum 1 1 3 2 2 1 1 1 1 1.... cies is confined to the hot deserts around the Arabian Pennisetum divisum 11111+ + +11.... Gulf, occupying enormous areas in Central and North­ Cyperus aucheri 2 1 + 1 ...... eastern Arabia. VESEY-FITZGERALD (1957) has CS and DS of Helianthemo-Farsetietea and Aervo-Faaonion stated there a Rhanterium-be\t between the central Helianthemum lippii ...... 1111 red-sand associations and the Stipa- steppe (Rhanterie- Farsetia stylosa ...... 2 1 1 1 tum s.l. sensu ZOHARY 1973). Rhanterium is an oli- Monsonia nivea ...... 2222 gospecific genus of saharo-arabian distribution. Be­ Fagonia ovalifolia ...... 2 + 2 1 sides the east-arabian Rhanterium epapposum , we Atractylis carduus ...... + + + 1 + + find the vicarious Rhanterium suaveolens in the Nor­ thern Sahara of Algeria and Morocco in Zillion CS ChrozoDhora sabulosa-comm. and Cutandietea macropterae- communities. Chrozophora sabulosa .++.+1++1 + . . . . The second common species is Panicum turgi- dum, a grass of sub-saharo-sindian distribution. It is Cutandia memphitica 1112212111.... also an effective sandbinder as well as an important Eremobium aegyptiacum 1 + .+ + 11 + + + . + . . forage plant. Reproduction is mainly vegetative. Like Silene villosa ...+222222+... in Qatar (BATANOUNY 1981), it is associated in Du­ Moltkiopsis ciliata + . 2 1 1 1 . . 1 ...... bai with Pennisetum divisum. Arnebia hispidísima ...... +2222 Within the inland dune ecosystem, we can distin­ Plantago boissieri . .++.22221 + .+ + guish at least three different habitats: High dunes, Hippocrepis bicontorta ..1. +11111++.. low dunes and dune valleys. Neurada procumbens . + 1.1+ + +1.+1.1 The high red dunes, mostly fixed, have relicts of Lotus halophilus . . . .+ + 11 + 1+ + .+ the original Prosopis- forest. Prosopis cineraria is a Gisekia pharnaceoides . + . . + + + . + ...... phreatophyte, concentrated at the margins of large Schismus barbatus ....+ + ...... + Comoanions Tab. 3 Aristida adscensionis 11121111 1 1+ + 1 + Panicum turgidum-Rhanterium epapposum-vegetation Centaurea pseudosinaica . + .1+21112 + 1.1 complex Launaea mucronata . + .+ +.+1 . 1 +1+ + (Transect II in the inland dune ecosystem) Launaea capitata . + . . .++.+ + +.1 + Heliotropium kotschyi . . + + ...... Further rare species: Bassia muricata ....+...++. ... in 2: Phoenix dactylifera (seedling) +; Paronychia arabica .++.+ + + 1+1++1. in 4: Astragalus biabauensis +; in 5: Hammada salicornia +; Tragus racemosus ..++1 . + +. . + ... in 9: Zygophyllum simplex +; in 12: Hippocrepis constricta +; Cenchrus ciliaris .. + . .. + ...... in 14: Chenopodium murale +. Asphodelus fistulosus ...... + . 1 Locality: All relevés taken in fenced area near Nakhali-Palace Polygala cf. irregularis ...... + . + east of Dubai City, 17.3.1987. Tab. 4 Releve N°. 1 2 3 4 5 6 7 8 Pseudogaillonio-Euphorbietum laricae

CS of the association and higher units Further rare species: Pseudogaillonia hymenostephana 1 1 + + . . . . in 2: Polygala erioptera +, Cyperus jemenicus +, Savigna Jaubertia aucheri .1.21. + . parviflora +; in 4: Crotalaria aegyptiaca 1, Blepharis ciliaris 1, Euphorbia larica 2 1 1 ++ 1 1 2 Capparis cartilaginea 1; in 5: Grewia tenax +, Ochradenus Perennial herbs and grasses of rockv environment arabicus +, Vernonica arabica +, Senecio flavus +; in 7: Chenopodium murale 1. Stipagrostis foexiana 1 + . . . + . + Locality: Relevé 1 -3 , 6 -8: Quarn Nazwa, 18.3.1987; Rel. 4 -5 : Viola cinerea . . . 1 + 1 . . Jabal Buhays, 19.3.1987. Morettia parviflora . . . 1 + . . . PS of ruderal variant Aizoon canariense ...... 1 + dune fields and along wadis. It ranges from Hadra- Atractylis carduus ...... + + maut and Mascat to the Sind desert, forming mixed CS of Anabasetea. Hammadetea and Acacietea open woodlands with Acacia tortilis and other Aca­ Gymnocarpos decander 1 + 1 + + + 1 1 cias. Some dense relict stands in the Central Desert Hammada salicornica . + 2 + + 1 1 1 of the Emirates are endangered by grazing and cut­ ting and by the dramatic decline of the groundwater Rhanterium epapposum + + . + . . . . table over the last two decades (see Plate 54 in the Reseda aucheri . . + + . + . . UAE Atlas). Like in Dubai, also in the Wahiba Sands Haplophyllum tuberculatum . . . + + . . . in Oman no regeneration can be registered outside Acacia tortilis + + . 1 1 + + 1 protected areas (BROWN 1988). From this habitat Lycium shawii . + .++. 1 1 type, no relevés are available. Cymbopogon commutatus 1 + . 1 + . . + The floristic composition of the lower dunes and Companions (perennial) of the dune valleys has been documented by relevés Aerva javanica 1 1 + 1 1 1 + + (Tab. 3) and their vegetation will be discussed in de­ tail. Reichardia tingitana + 1 1 + + + 1 + Forsskaolea tenacissima .. + ..11 + Leptadenio-Rhynchosietum schimperi ass. nov. . + . + .... Salvia aegyptiaca Tab. 3, rel. 1-10, type relevé N°. 6 Leucas inflata ...11... Fagonia bruguieri ...11... The lower, partly fixed dunes are colonized by Companions (annual) the shrubs Leptadenia pyrotechnica, Calligonum co- Sclerocephalus arabicus 1 1 1 + + 1 1 + mosum and Rhynchosia schimperi, by the tussock Cenchrus pennisetiformis .+211121 grasses Panicum turgidum and Pennisetum divisum Seetzenia lanata . + + + + . + and by psammophilou« annuals (Cutandia memphi- tica , Silene villosa, Eremobium aegyptiacum and Arnebia hispidissima + . + + . 1 + . others). This Leptadenia-Rhynchosia-Panicum- com­ Cometes surratensis . . 1 + + 1 + . munity replaces the original Prosopis woodlands, Aristida abnormis . . 1 + + 1 1 . which have been almost everywhere destroyed by Ifloga spicata . . + . + + 11 grazing and wood cutting. Character species of the Plantago ciliata . .++ + +.+ new association descibed here are Rhynchosia schim­ Rumex vesicarius + . . + + + . . peri, Tribu lus arabicus and Coelachyrum piercei. Enneapogon desvauxii 1 + . + .+ . . Rhynchosia is a densely grey villous shrub. As it is a Tetrapogon villosus 11 ..++.. high palatable species, it is nowadays difficult to find good specimens and near Nakhila Palace it has been Hippocrepis constricta . . 1 . + 1 . + found only inside the fenced area. The species is also Argyrolobium roseum . .+ ..+ .+ known from dune fields south of Jeddah, from the Astragalus eremophilus + + + . . . . . Wahiba Sands in Oman and is restricted in the UAE Plantago ovata 1 . . + . 1 . . to the inland dune field. Tribulus arabicus is endemic Dactyloctenium scindicum in Southeastern Arabia, from Bahrain to Oman. Co­ Notoceras bicorne elachyrum piercei occurs in Southern Arabia and in Oligomeris subulata + + . . . Makran. Both are psammophytes. Character species Medicago laciniata + + . . . of a high rank syntaxon are Leptadenia pyrotechnica Erucaria hispánica ...11 and Calligonum comosum. Leptadenia is of south- saharo-sindian distribution. In the Sahara, it dif- ferenciates the southern form of the Calligonum como- poverished outlier of the Aervo-Fagonion. This synta­ sum-Aristida pungens-c ommunity Quezel 1965 and xon has a transitional position between the subtropi­ enters also into Acacio-Panicion- communities sensu cal class Boerhavio-Tephrosietea (BARRY et al. 1986) BARRY et al. (1981, 1986). The richly branched and the extratropical class Helianthemo-Farsetietea leafless shrub Calligonum comosum is distributed (FOUCAULT 1993). A Helianthemum //pph-commu- from Iran to Morocco, always colonizing deep sand. nity with more saharo-arabian elements is reported Further character species might by found among the from southern Jordan by BAIERLE (1993). psammophilous shrubs (Heliotropium digynum to Po- Ivcarpaea repens ), but more information about the The ephemeral Chrozophora sabulosa-commu­ ecology and sociology of those species is necessary. nity Synsystematics: In a very broad community After rainfall, mostly in spring, short-lived annuals concept, like that of VESEY-FITZGERALD (1957), the build a green carpet (the »acheb«) on dunes and in v/hole vegetation complex of the inland dune fields sandy depressions. They finish their life cycle, when of Dubai would be included in the Rhanterium-steppe- the sand is drying out. Some authors, for example type. In a community concept, based on dominant ZOHARY (1973), interpret this group as a stratum of species, this would be split up in numerous units. the perennial sand community. But GUINOCHET BATANOUNY & TURKI (1983) for example described (1951) has already realized in his studies in the Mau­ from Qatar different communities with the following retanian Sahara, that this unit is quite independent species: Rhanterium epapposum, Panicum turgidum, from the perennials. It can enter different shrub com­ Pennisetum divisum, Leptadenia pyrotechnica, Aca­ munities, even halophytic groups, as a short-lived cia tcrtilis, Lycium shawii. We follow a concept in overlay if the sand is thick enough (10 cm and more) between the two previous ones. We interpret the ca­ to »isolate« them from the substrate of the deep roo­ tena of Fig. 6 and the sampling-transect of Tab. 3 as a ting perennials. These species grow in an environ­ repetitive pattern of the ecotopes: dune ridges, dune ment which is quite different from that of the peren­ slopes and dune valleys. The whole forms a vegeta­ nials. They do hardly interact with them. They are an tion complex of three communities (the stratum of independent plant community. The species group the annuals will be discussed separately). They can from Cutandia memphitica to Schismus barbatus also be found in another combination of communities (Tab. 3) is provisionally named Chrozophora sabu- and can be elements of other contact series. /asa-community. It is the corresponding unit to the The Leptadenio-Rhynchosietum is the south­ salt-tolerating Frankenio-Zygophylletum. eastern outpost of a saharo-arabian class of perennial Synsystematics: GUINOCHET (1951) proposed vegetation on mobile, non saline dunes with Calligo­ the name Cutandietea for a class of ephemeral sand num comosum . This syntaxon has still to be defined vegetation in the Saharo-Arabian desert belt. From by comparative studies with the Aristidetalia pun- his class characteristics, Cutandia memphitica , Ere- gentis Guinochet 1951 from the northwestern Sahara mobium aegyptiacum (= Malcolmia a.), Hippocrepis and the Haloxylo-Retametalia Zohary 1973 from Nor­ bicontorta, Neurada procumbens, Lotus halophilus thern Arabia and Sinai. Further syntaxa, which have and Moltkiopsis ciliata occur in Dubai. The east-sa- also to be taken into account are: The Hammadetea haro-arabian and nubo-sindian Arnebia hispidissima salicornicae Zohary 1973, the Acacio-Panicion (BARRY is replaced in the Mauretanian Sahara by A. decum- et al. 1981), the Cassio-Panicion Foucault 1993 and bens, in the sand deserts of Southern Iran by A. late- the Pseudosavannas with Acacia tortilis and Panicum bracteata (FREITAG 1986). The night-flowering Si- turgidum sensu ZOHARY (1973). For the moment, lene villosa is also the naming species of the south- there exist more names for high rank syntaxa than moroccan Echio-Silenion villosae (LEMEE 1954). detailed studies. The association in Dubai is differentiated from this alliance by subtropical and eastern elements like Helianthemum lippii-Fagonia ovalifolia-com- Chrozophora sabulosa (omano-makranian-irano-tura- munity nian) and Gisekia pharnaceoides. Further studies Tab. 3, rel. 11-14 are necessary to clear the differences between the Cutandietea and the following groups: Notoceretea The dune valleys with a stony surface layer are bicornis Nègre 1956 em. Foucault 1993 (the un­ colonized by low shrubs. Helianthemum lippii, Mon- named order 3 there!), Schismo-Crithopsietea sonia nivea, Fagonia ovalifolia and Farsetia stylosa (BRULLO & FURNARI 1978) and the therophytes of occur there. They are mentioned by BARRY et al. the Haloxylo-Retametalia Zohary 1973. Northern (1986) as characteristic species of the Aervo-Fagoni- outposts of an ephemeral psammophytic vegetation on , an alliance, which occupies similar relief units in unit with Eremobium aegyptiacum and Silene villo­ the Southern Central Sahara. The rankless Helianthe­ sa in the Wadi Araba are mentioned by BAIERLE mum lippii-Fagonia ovalifolia- community is an im­ (1993). 5.3 The stony desert nia] aucheri. Both species have an omano-makranian area. Pseudogaillonia is found on bare rocks from The stony ecosystems in Dubai comprise very diffe­ Mascat to the Punjab, Jaubertia on stony foothills and rent ecotopes like gravel plains, rock outcrops and rocky slopes from the Musadam mountains to the the mountain area itself. Differenciating ecological coastal mountains of southern Iran, Afghanistan and factors in the stony environment are inclination and Baluchistan. The Pseudogaillonio-Euphorbietum is exposure of slopes, altitude, gravel size and depth of very similar to the variety 3 of the Commiphora myr- the sediment layer. We will go into details only for a rha-Euphorbia larica-c ommunity sensu FREY & community on bare rock. The vegetation of the gravel KÜRSCHNER (1986), growing on karstic limestone at plains and of the mountainous areas will be outlined lower altitude of the mountain ranges south of Mas- very briefly. cat. On rocky slopes with a layer of boulders and mo­ re sandy material in the fissures (relevé 5-8), Pseudo­ Pseudogaillonio hymenostephanae-Euphorbie- gaillonia is missing. tum laricae ass. nov. The two Rubiacee are associated with Euphorbia Tab. 4, type relevé N°. 1 larica , an almost leafless, much-branched shrub with smooth, fleshy stems. It colonizes rocky slopes at low Within the inland dune system and also within and medium altitudes in the Musadam peninsula and the stony pediment, we find some rock outcrops like in southern Iran, limestone as well as schists. In South­ Qarn Nazwa near the Hatta road and Jabal Buhays. west Arabia this species is replaced by Euphorbia At those localities the relevés of Tab. 4 have been ta­ schimperi , on Masirah-Islands by Euphorbia masiha- ken. The outcrops are built by compact limestone rensis, both members of the section Tirucalli within and boulders and are partly covered by a thin sand the genus Euphorbia. layer (Fig. 7). The rock surface shows microerosion, a Further species of high constancy are Gymnocar- form of karst weathering caused by frequent dew and pos decander, Hammada salicornica (= Haloxylon s.) fog. This is also indicated by epilithic lichens. and the tufted grasses Cymbopogon commutatus and On bare rock (relevé 1-4), with sparce vege­ Stipagrostis foexiana. Gymnocarpos is widespread in tation cover and in southern and western exposure, stony deserts of the saharo-arabian region (Anabase- two Rubiacee are growing in rock fissures: Pseudo- tea-communities in Egypt and Palestine, Gymnocar- gaillonia hymenostephana and Jaubertia (= Gaillo- po-Atractyletalia Quezel 1965 in the Northwestern Sahara), Hammada is confined to the hot sand de­ Tab. 5 serts in the Middle East and characterizes psammo- Saccharo-Nerietum mascatense philous plant communities (Hammadetea salicorni- cae Zohary 1973). In the UAE, this leafless shrub is

Releve N°. 1 2 3 4 the dominating plant of the sandy depressions within the red inland dunes, also growing on sand accumu­

CS of the wadi communitv lations over rocky slopes. On gravel plains it forms Saccharum griffithii 3 3 2 2 large mounds by fixing /and. After rainfall, a herb Nerium mascatense 1 1 2 1 layer with Sclerocephalus arabicus, Cenchrus penni- Dyerophytum indicum + + 1 setiformis, Cometes surattensis and other annuals CS of the ODen woodland comm. on sloDes develops. This stratum requires further studies. Moringa peregrina + + Synsystematics: The Pseudogaillonio-Euphor­ Lycium shawii + 1 bietum can be included into the Euphorbietea laricae Dodonaea viscosa + Zohary 1973. This class is of omano-makranian distri­ HvaroDhilous herbs bution. Further communities, already described, are Parietaria lusitanica + 1 + the Euphorbia larica-Gaillonia aucheri- association Zo­ Onychium melanolepis + + hary 1963, the Euphorbia larica-Sphaerocoma auche- Galium setaceum decaisnei + + /Tassociation Zohary 1963, the Commiphora myrrha- Comoanions Euphorbia larica- community around Mascat (FREY & Tephrosia apollinea + 1 2 1 KÜRSCHNER 1986) and a still undescribed associati­ Echinops spec. 1 1 + on with Euphorbia larica, Barleria Candida and Iphio- Brachypodium distachyon + + na horrida in the Northern Oman Mountains (GHAZ- Zoegea purpurea + + ANFAR 1991). The first group is the central associ­ Ziziphus spina-christi + ation of the class and the relevés 5 -8 can be included Forsskaolea tenacissima + in this syntaxon. It is know also from southern Iran Filago desertorum 1 near Bandar Abbas and from Jabal Akhdar in Oman Senecio flavus + (MANDAVILLE 1977). The Euphorbio-Gaillonietum has higher cover values than the Pseudogaillonio- pftorbietum, it grows on less extreme rocky slopes cut into the bare rock, the wadi bottom is covered nd on boulders. Differential species of a ruderal vari­ with boulders, stream velocity during erratic water ant are Aizoon canariense and Atractylis carduus (re- flow is high. Some finer sediments are collected by j*evés 7_ g> jab. 4). In higher altitude, the Euphorbio- the dense clumps of the wild sugar cane. The relevés Gaillonietum is followed by the Euphorbia larica- from Table 5 have been taken in Wadi Ham south of Convolvulus acanthoclados-c ommunity, stated by the Masafi-Bethha-road (Fujeirah) on 20.3.1987. Cha­ MANDAVILLE (1985) in the Musandam Mountains racter species of the Saccharo-Nerietum mascatense and by ZOHARY (1963) in southern Iran. Even hig­ are the highgrowing tufted grass Saccharum griffithii her up in the Hajar-mountains we have a separate al­ and the evergreen shrubs Nerium mascatense and titudinal belt in climatic and floristic respect: higher Dyerophytum indicum. All these species are of oma­ precipitations and relicts of an evergreen sclerophyl- no-makranian distribution: The same association can lous woodland with Moringa peregrina , Dodonaea be observed in the Oman mountains as well as in wa­ viscosa and Reptonia mascatensis (= Monotheca bu- dis in Southern Iran and Pakistan. The salt secreting xifoiia). This vegetation belt, which follows the Eu­ Plumbaginaceae Dyerophytum indicum is an indo-ma- phorbia larica-zone, has been studied by MANDAVIL­ layan relict in Arabia (KÜRSCHNER 1986a). LE (1985) in the Musandam Mountains and by MAN­ The Saccharo-Nerietum is in contact to shrub DAVILLE (1977) and GHAZANFAR (1991) in Nor­ communities of mountainous character with Moringa thern Oman at the Jabal Akhdar. peregrina and Dodonaea viscosa. On fine, humid The genus Gaillonia s.l. (LEONARD 1984) in­ sand between the boulders and gravels, a synusium cludes Choulettia (one species in the northwestern of hygrophilous herbs (Parietaria lusitanica ) and ferns Sahara), Jaubertia (one omano-makranian species), ( Onychium melanolepis) develops after the run-off. Pseudogaillonia (one omano-makranian species), Pe- Synsystematics:DEIL (1986) has shown, that on trogaillonia (three species, west-saharo-sindian) and the Arabian peninsula two wadi vegetation types exist: Neogaillonia (22 species, from Socotra to Turkmeni­ An extratropical one with Apocynaceae and a tropical stan). The monospecific genera seem to be confined one with Jatropha-species. The wadi communities in to the rocky environment. The Pseudogaillonio-Eu- the UAE belong to the extratropical type. Wadi com­ phorbietum is vicarious to a plant community in sou­ munities with Apocynaceae (Nerium, Rhazya ) and tall thern Morocco and Algeria. There, Gaillonia (= growing perennial grasses of the Tribus Andropogo- Choulettia} reboudiana and Gymnocarpos decander neae, Subtribus Saccharinae (Saccharum, !mperata), are associated on rocks, boulders and stony pedi­ often in contact or associated with Tamarix species, ments. They are character species of the Atractylion are recorded from the whole saharo-arabian and nubo- babelii Lemée 1953 (Gymnocarpo decandris-Atracty- sindian region. Vicarious communities to the Saccharo letalia serratuloidis Quezel 1965). griffithii-Nerietum mascatense are the Saccharum kaj- The stony gravel plains offer good conditions kaiense-Nerium indicum community from Iran and only for deep rooting perennials which can reach the Punjab, the Saccharum spontaneum-Tamarix nilotica- ground water level. An open woodland can be found T aphylla community from the Yemeni lowland, the here with Acacia tortilis , A. ehrenbergiana, Lycium Nerio-Tamaricetum niloticae Quezel 65 from the cen­ shawii and Elammada salicornica. When the tree tral Sahara and, as the northernmost outlier, the Equi- layer is destroyed, Pulicaria glutinosa becomes the seto-Erianthetum ravennae Br.-Bl. & Bolos 1957 from dominant species. Along small runnels and wadis, a intermittent rivers in the Ebro basin in central Spain. kind of gallery-forest with the phreatophytes Pro- The syntaxonomy of those wadi communities is sopis, Ziziphus and Ficus (see Fig. 7) can be found. still quite unclear. It must be based on supraspecific taxa. Until more records are available from South­ west Asia, the Saccharo-Nerietum mascatense is the 5.4 The Wadis only association of the omano-makranian alliance Saccharo griffithii-Nerion mascatense all. nov., According to frequency and intensity of water flow, vicarious to the southwest-mediterranean Imperato- stream velocity, depth of groundwater level and grain Erianthion. Both can be included in the class group size of the sediments we can distinguish four wadi Imperato-Tamaricea Bolos 68. vegetation types in the UAE. Just one is described When the wadi bottom is broader, filled up with here in detail. gravel and sandy sediment which store groundwater, the wadis are intensely used by man. This agricultu­ Saccharo griffithii-Nerietum mascatense ass. nov. ral oasis wadi type is covered by date palms (Phoenix Tab. 5, type releve N°. 1 dactylifera), mango trees (Mangifera indica ), pome­ granate (Punica granatum), various citrus trees and Deep incised, canyon-like wadis of the mountainous other fruit trees. Remnants of the original vegetation area belong to this type. The valley slopes are often are Nerium mascatense, Ficus salicifolia and Acacia nilotica. In the tree shadow on walls with dripping 6 Concluding remarks water, along water courses and irrigation channels, we find the Adianto capilli-veneris-Epipactidetum The general zonation of the landscape units in the UAE veratrifoliae Deil 89, for example in Wadi Difta. (coastal dunes, inland dunes, stony desert) is similar to In the alluvium of wadis emerging from the that in other regions of the Arabian-Persian Gulf and of mountains, Physorrhynchus chamaerapistrum is grow­ the Read Sea coasts. If we have a closer look at the ing (see Fig. 7). This species is also endemic to the flora and the vegetation cover in Dubai, we can state omano-makranian region. It characterizes a community quite different chorological affinities of the plant com­ of its own, which has still to be studied in detail. Outsi­ munities. Most of the associations described here (the de the mountains, the wadis are filled up with deep de­ Cornulaco-Sphaerocometum, the Leptadenio-Rhyncho- posits. On gravels we find the Acacia tortilis-Rhazya sietum, the Pseudogaillonio-Euphorbietum and the stricta-type, very similar to the vegetation of the foot- Saccharo-Nerietum) can also be found in Southern Iran plains and stony gravel pediments. On fine deposits the and Northern Oman. These omano-makranian links are Tamarix-Calotropis-type indicates groundwater. based on common climatic conditions in the southern

Tab. 6 Syntaxonomical survey

Syntaxonomical survey

H alo peplido -Sua edetea Knapp 1968 (pp. syn. Sua edetea fruticosae deserta Z ohary 1973) Halopeplidetalia perfoliatae Knapp 1968 ? Halopeplidetum perfoliatae ass. nov. ex Kassas 1957 regional race with Zygophyllum qatarense Salsolo-Suaedetalia Knapp 1968 ? Cornulaco monacanthae-Sphaerocometum aucheri ass. nov. Subass. typicum Subass. halopyretosum mucronati subass. nov.

Frankenietea pulverulentae R iv -M t z . ex Castroviejo & P orta e m . B rullo 1988 ? Zygophyllion simplicis all. nov. prov. Frankenio pulverulentae-Zygophylletum simplicis ass. nov.

H a m m a d e te a salicornicae Z ohary 1973 7 Acacio-Panicion Barry et al. 1981? / Leptadenio-Rhynchosietum schimperi ass. nov.

B o e r h a vio -T ephrosietea B arry et a l . 1986 ? Aervo-Fagonion Barry et al. 1986 Helianthemum lippii-Fagonia ovalifolia-community

CUTANDIETEA MEMPHITICAE GUINOCHET 1951 ? pp. Echio-Silenion villosae Lem6e? Chrozophora sabulosa-community

Euphorbietea lar ica e Z o h ary 1973 7 7 Pseudogaillonio hymenostephanae-Euphorbietum laricae ass. nov. Euphorbia larica-Gaillonia aucheri-association Zohary 1963

Im per a to -T am a r ic ea B olos 68 ? Saccharo griffithii-Nerion mascatense all. nov. Saccharo grifTithii-Nerietum mascatense ass. nov. art of the Gulf, a common vegetation history and the References drying out of the Strait of Hormuz in recent geological times. The chorospectra of these communities show BABIKIR, A.A. 1984: Vegetation and Environment on the transitional character of the study area from the Pa- the coastal sand, dunes and playas of Khor El- leotropical to the Holarctic Kingdom. The taxa of tropi­ Odaid Area, Qatar. Geo Journal, 9: 377-385. cal origin (the sudanian and eritreo-arabian geno-ele- BABIKIR, A.A. 1985: On the distribution of rainfall ments) are predominant among the perennials. The si­ over the Sultanate of Oman. Geo Journal, 11: milarities to the Northern Gulf (Kuwait) are not so 165-172. strong (HALWAGY & HALWAGY 1974). BAIERLE, H.U. 1993: Vegetation und Flora im süd­ The salt-influenced coastal sabkha system is colo­ westlichen Jordanien. Dissertationes Botanicae, nized by a vegetation complex, which is composed of 200. Stuttgart. the same plant communities in Qatar, Mascat and on BARKMAN, JJ. et al. 1986: Code of phytosociologi- both sides of the Read Sea. This complex is of circum- cal nomenclature. Vegetado, 67: 145-195. arabian distribution and always shows the same zo- BARRY, J.P. et al. 1981: Le problème des divisions nation. The halo-series is ruled by salt content, degree bioclimatiques et floristiques au Sahara algérien. and frequency of inundations and by the intensity of Note III. Naturalia monspeliensia, Sér. Bot., Fase. wind erosion. Regional attributes to the common 44: 1-84. species and communities are vicarious Limonium and Zy- BARRY, J.P. et al. 1986: Le problème des divisions gophyllum species. These genera can be used as supra- bioclimatiques et floristiques au Sahara. Note V. specific character-taxa to define this vegetation complex. Ecología Mediterránea, 12: 187-235. The annual vegetation units have more floristic BATANOUNY, K.H. 1981: Ecology and Flora of Qatar. affinities to the extratropical desert vegetation than Oxford. the perennial ones. Most of the species are of saharo- BATANOUNY, K.H. AND TURKI, A.A. 1983: Vegeta­ arabian distribution and of extratropical origin. They tion of South Western Qatar. Arab. Gulf J. scient. are spring annuals and are reacting to the mediterra­ Res, 1: 5-19. nean rainfall regime in Dubai. One perennial plant, BATANOUNY, K.H. AND ISMAIL, A.M. 1985: Phyto- which connects the northern and southern parts of ecological observations in Northern Oman. Qatar the Gulf, is Rhanterium epapposum. Univ. Sei. Bull, 5: 87-129. The associations described here are sufficiently BEUG, H.J. 1971: Über die Pollenführung von Sedi­ characterized, both from the floristic and from the mentproben aus dem Persischen Golf und dem ecological point of view, but their syntaxonomical po­ Golf von Oman. Meteor Forsch. Ergebn. Reihe C, sition (see the scheme Tab. 6) is sometimes prelimi­ 7: 1-3. nary, because a summarizing conspectus of the saha- BORNKAMM, R. AND KEHL, H. 1990: The plant ro-arabian vegetation has not yet been made. communities of the Western Desert of Egypt. Phytocoenologia, 19: 149-232. The authors are grateful to Mr. PLATT (Dubai Wild­ BRAUN-BLANQUET, J. 1964: Pflanzensoziologie. Wien. life Center), Mrs. JONGBLOED (Dubai) and Mr. BROWN, K. 1988: Ecophysiology of Prosopis cinera­ GABRIEL (Hamburg) for support of the field work, to ria in the Wahiba Sands, with reference to its the staff of the Royal Botanical Garden Edinburgh, es­ reafforestation potential in Oman. J. Oman Stu­ pecially Mr. HEDGE and Mr. MILLER for their help dies, Spec. Rep, 3: 257-270. in the determination of the specimens, to Mr. BRULLO, S. 1988: Le associazioni della classe Fran- KUKKONEN (Helsinki) for identifying Cyperus, to kenietea pulverulentae nel Mediterráneo centrale. 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Deil Ulrich & Müller-Hohenstein Klaus Department of Biogeography, University of Bayreuth, D-95440 Bayreuth, Germany