Biology of the Central Desert of Oman
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TurkJBot 28(2004)65-71 ©TÜB‹TAK BiologyoftheCentralDesertofOman ShahinaAGHAZANFAR Herbarium,RoyalBotanicGardens,Kew,Richmond,Surrey,TW93AB,UK Received:13.08.2002 Accepted:29.01.2003 Abstract: AbiologicalsurveyofthecentraldesertofOmanwasdoneusinglongdistancetransects.Vegetationwassparseand consistedof200+plantspecies,22speciesofmammals,17speciesofreptilesandamphibians,andmorethan50speciesofbird s (migratoryandresident).Threemainvegetationtypeswereidentifiedbasedongroundsubstrateandthedominanceofspecies. ThesewerecommunitieswithAcacia Willd.,Zygophyllum L.,andopenwoodlandsofProsopiscineraria (L.) Druce.Over-grazingand developmentinthecentraldeserthasledtoconcernsovertheconservationofthedesertecosysteminOman. KeyWords: ARABIAOMAN,plantcommunities,life-forms,conservation Introduction Emiratesborderisdatedbackto104ka,whichsuggests i.Boundariesofthecentraldesert fluvialactivityassociatedwiththelastinterglacialclimatic optimum(Glennie&Singhvi,2002;Juyal&Singhvi, ThecentraldesertofOmanliesapproximately 1998). between18º and22º30’Nand52º and59º Eand occupiesabouthalfofthecountry’slandsurfacearea Geologically,theunderlyingrockofthecentraldesert (Fig.1).Itstretchesinthenorthfromthesouthernend isalmosthorizontal,mid-Tertiarylimestonefromthe ofthefoothillsoftheHajarMountainsandreachesinthe OligoceneandMioceneandrepresentssea-bedlevelsat southtotheedgeofthenorth-facingslopesoftheDhofar thetimeofdeposition(Hughes-Clarke,1990).The Mountains.Inthewestthecentraldesertpetersintothe presentflatnessofthelimestone(rockunitsclassifiedas sandseaofRub’al-Khali,andintheeasttoRamlat FarsandHadhramaut)showsthattherehasbeenlittle Wahibahandtheeasternescarpments(Huqfandthehills movementofearthsincetheirdepositionsome30million abovetheSahilal-Jazir).Generally,thecentraldesert yearsago.Inthenorth-westernregionofthecentral formsavastfeaturelessplain,withlowgraveloutcrops desertliesalargesabkha,theUmmas-Samim. andgravelplainscoveredwithaeoliansand.Broadalluvial SeveralwadisdraintheHajarmountainsandthe fans,shallowwadisanddrainagechannelsthatdrainthe southernescarpmentsandflowintothecentralplains. northernandsouthernmountainsreachthenorthernand Formostyearstheflowissubsurface,butwhenrainsare southernpartsoftheplains,withonlyafewreachingthe exceptionallyheavyorwhenthereisatropicalstorm, centralparts.Inthenorth-eastandwestlowstabilised surfaceflowispresentinsomeofthesewadis. andunstabilisedsanddunesborderthecentraldesert. Nevertheless,vegetationinthesewadisisricherthanin Thenorth-westerndunesseemtohavebeenbuiltlargely thesurroundingareas.Twomainwadisflowsouthfrom bywindsassociatedwiththenorthernShamal,which theHajarmountainsandreachthecentralplains:Wadi blowsacrosstheArabianGulffromtheNNWandveers Umayri,whichflowswestintotheUmmasSamim,and SWtowardsthemountainsofYemen(Glennie&Singhvi, WadiHalfayn(combiningwithotherwadis)flows 2002;Juyal&Singhvi,1998).Thesandsarequite southeastandreachesnorthoftheBaral-Hikman distinctivebecauseofthepresenceofacoatingofred peninsula.Inthesouthernpartofthecentralplainsthe ironoxideonahighproportionofthesandgrains,a Mukhayzanah,Rawnab,Ghadun,QitabitandRibkut characterfarlesspronouncedelsewhereinthesandsof wadisdrainthesouthernescarpmentsandflowintothe Oman,suchasintheeasterndesert.Thealluvialfanand centralplains.Mostoftheareaofthecentraldesertof theaeolioniteinthenorth-westpartofOmanclosetothe Omanliesbetween100and250ma.s.l.,slopinggently 65 BiologyoftheCentralDesertofOman fromtheeasternescarpmentswestwardstowardsthe showsamaximumof4000cm 3 duringMarchanda sandsoftheRub’al-Khali. minimumofc.2500cm3 duringJanuary,May,Juneand Formostofthecentraldesertlong-term December(Fisher&Membery,1998;Stanley-Priceetal., meteorologicaldataarenotavailable.Meteorologicaldata 1988).Thisisaconsiderableamountofmoisturethat fromstationspresentatFahud,Ja’alooni,MarmulAir condensesontreefoliageanddripstothegroundandis StripandThamraitwouldbecomparableandcouldbe potentiallyavailabletothefloraandfaunainanotherwise usedtodescribeclimaticconditionsinthecentraldesert extremelyaridregion. (Table1,Fig.1). ThemaindevelopmentsinthecentraldesertofOman Climaticdatashowthehyper-aridityofthecentral aretheoildrillingstationsofPetroleumDevelopmentof desertwithmeanannualrainfallnotexceeding48mm Oman(PDO),whicharelocatedatdifferentlocationsin andmeanannualtemperatureofabove26ºC.The thedesert.Severalhumansettlementsandtheirlivestock, absolutemaximumtemperaturesreachabove50ºCand mainlycamelsandgoats,arealsopresentinthecentral theabsoluteminimumtemperaturesfallbelow6ºC,a desert.Somearenomadic,suchastheHarasistribeon featuretypicaltodeserts.Ananalysisofthe12-month theJiddatal-Harasis,whileothershavemadepermanent auto-correlationcoefficientoftotalmonthlyrainfalland homeswithhelpfromthegovernmentandPDO. meanmonthlytemperatureandcoefficientofvariations Asaunit,IclassifythecentraldesertofOmanasan ofmeanannualrainfallandmeanannualtemperature hyper-aridareawhichhasnonaturalwaterseepage, showsthatthereisverylittleinter-annualvariationof springs,orpermanentorseasonalwaterbodies,and temperatureandthattotalannualrainfallisexceptionally whichreceivesonlysporadicrainfallfromoneyeartothe variablebetweenyearswithlittleindicationofseasonality other,oftenwithseveralyearsbetweenrainfall. (Fisher&Membery,1998).Rainhasbeenknowntofall Method innearlyallmonthsoftheyear,thoughthemean monthlytotalfor11yearsofdataarehighestduring Thevegetationofthecentraldesertwassurveyed FebruaryandAprilforallstations.MaytoDecemberare alongtransectsmadeinalldirections(butfollowingtrack thedrymonthsinMarmul,FahudandJa’alooniandJuly roads)fromthemainofficesofPDOoilstations.All toNovemberinThamrait. specieswererecordedandidentifiedalongthetransects. Asthevegetationwasverysparseinmostareas,species Fogoccursintheeasternpartofthecentraldesert. wererecordedevery500m.Allspecieswererecorded Dataontheannualmeannumberoffogdaysarenot whentransectscrossedshallowwadis,andallwoodlands availableatanyofthemeteorologicalstationsmentioned werevisitedandspeciesrecorded,andthestateofthe inTable1;however,fogmeasurementshavebeenmade woodlandassessed.Voucherspecimenswerecollectedof forJa’aloonionaregularbasisfor1992-1993.Datafor speciesthatcouldnotbereadilyidentifiedinthefield. theJa’aloonistationshowthatfogoccurredonan ThesewerelateridentifiedattheNationalHerbariumof averageof54daysayearduringeverymonthsofthe theMinistryofNationalHeritageandCulture,Oman,and yearexceptJuly.Precipitationfromfogmeasuredfrom attheHerbarium,RoyalBotanicGardens,Kew.The depositiononamultidirectional1m 2 meshcollector Table1. ClimatedataofthecentraldesertofOmanbasedon10-yeardatafrom1985-1995.(FromFisher& Membery,1998). Mean Meanannual Absolutemaximum Absolutemaximum Meanmonthly MeterologicalStation rain temperature temperature temperature maximumrange (mm) (ºC) (ºC) (ºC) (ºC) Fahud 24 28.8 50.7 5.6 19.4 Ja’alooni 39 26.6 49.0 6.5 19.3 MarmulAirStrip 41 27.7 49.0 5.4 17.3 Thamrait 48 27.1 46.0 1.6 16.8 66 S.AGHAZANFAR 60° 52° 53° 54° 55° 56° 57° 58° 59° 26° 26° ArabianSea 25° 25° GulfofOrman 24° 24° UAE 23° HajarMountains 23° Lekhwair Fahud(170m) WadiHalfayn SaudiArabia 28.8°C24mm 22° 22° Wahibah UmmasSamim Sands Fahud 21° Thumrait(467m) 21° 27.1°C47mm Masihar Bar alHikman Jaalooni Jaaluni(154m) 20° 26.6°C39mm 20° Bahja WMukhayznan Rima 19° t 19° en m rp ca s WGhadun E n Marmul(269m) r Marmul t s 27.7°C41mm a E 18° Thumrait N 18° DhofarMountains 17° 17° 0 50km 100km 52° 53° 54° 55° 56° 57° 58° 59° 60° Figure1.MapofOman. locationsfromwheretransectsweremadearegivenin sources(Harrison&Bates,1991),andtheirendemism Figure1. andRedListstatuswasascertainedfromFisher(1999). Allanimalandbirdlifeseenwasalsorecorded.Birds Severalspeciesofreptileswererecordedandidentified listsandtheirbreedingstatusfortheareawereobtained usingGardner(1999)andLevitonetal.(1992).For fromtheOmanBirdsRecordsCommittee(1998)and thoseinterestedinthefaunaofthecentralOmandesert, fromtheBreedingBirdsAtlasofOman(1998).Alistof Icansupply,onrequest,listsofthemammals,reptiles mammalswasmadeusingpublishedandunpublished andbirdsrecordedthere. 67 BiologyoftheCentralDesertofOman ResultsandDiscussion Ninetypercentofthespeciesofthecentraldesertare i.Flora:vegetationclassificationandlife-forms hemicryptophytesandchamaephytesandtheremaining phreatophytesandtherophytes(Fig.2,classificationof Thecentraldesertissparselyvegetatedwithalow life-formsafterRaunkiaer,1937).Afterrain,the diversityofspecies.Itisestimatedthattherearelessthan seedlingsofseveralannualsandperennials(mainly 25%ofthetotalspeciespresent(Ghazanfar,1991, Dipterygium glaucum Decne. and Heliotropiumkotschyi 1992b).Themainvegetationconsistsofscatteredtrees germinate,butonlyafewsurvivetotheyoungseedling of Acaciatortilis (Forssk.)Hayne,largeandsmallshrubs, stage. Zygophyllumsimplex L. isthemostcommon andperennialgrasses.Thewesternedgeofthedesert annualseenafterrain,especiallyinsandydepressions. adjoiningtheRub’al-Khalisandsisvegetatedwith dominantlypsammophilicvegetation.Thisconsistsof standsof Prosopiscineraria and Calligonumcrinitum Hemicryptophytes Boiss. inareaswherethedunesarestabilisedandsmaller shrubssuchas Zygophyllumqatarense Hadidi, Z. Chamaephytes hamiense Schweinf. and Heliotropium kotschyi (Ledeb.) Therophytes Guerkeatthebaseofdunes. Thevegetationofthecentraldesertcanbebroadly Phreatophytes classifiedaspartoftheAcacia-Zygophyllum-Heliotropium Geophytes VegetationType,whichistypicalofthecentralplainsof 0 1020304050 Oman,and Prosopis-Calligonum VegetationType,which %Totalspecies istypicalofthedunedesertsinOman(Ghazanfar,1991, 1992,1998a&b,1999a).Theinfluenceoffoginthe Figure2.Life-formsinthecentraldesertofOman. easternpartsofthedesertareahasincreasedthespecies