Lijie2012

Vegetationchangesduringthepast40,000yearsinCentralChinafromalongfossilrecordJieLia,b,ZhuoZhenga,KangyouHuanga,ShixiongYanga,BrianChaseb,c,VerushkaValsecchib,MatthieuCarréb,RachidCheddadib,*aDepartmentofEarthSciences,SunYat-senUniversity,Guangzhou510275,ChinabInstitutdesSciencesdel’EvolutiondeMontpellier(ISEM),UM2,CNRS,IRD,PlaceEugèneBatailloncc06134095,Montpelliercedex5,FrancecDepartmentofArchaeology,History,CultureandReligion,UniversityofBergen,Postbox7805,5020,Bergen,NorwayarticleinfoArticlehistory:AvailableonlinexxxabstractThispaperdescribesthepalynological,sedimentologicalandgeochemicalresultsobtainedfroma6mcoretakenfromLakeDajiuhuinShennongjiaMountains,centralChina,spanningthelast40,000BP.Thesiteislocatedinasubtropicalareawhichisknownforharboringmanyendemicspecies.ThepollenrecordshowsthatpastclimatechangesduringtheGlacialallowedthepersistenceofwarmtreesandevensubtropicaltaxa.Thepercentagesofarborealpollentaxavaryfrom40%beforeandduringthelastglacialperiodtow60%duringtheHolocene.Thed13CdataindicatethatthedominantvegetationwascomposedofC3plants.However,despitethecontinuouspresenceoftreetaxaaroundthesite,thetotalorganiccarbonindicatesthatthebiomasswasverylowduringtheglacialperiod(MIS3and2),relatedtothedominanceofconifersandevergreentreetaxa,whichareverylowbiomassproducers.Thetotalorganiccarbon(TOC)startedtoincreasesteadilyattheendofthelastglacialperiod(endofMIS2),whichreflectsthesharpincreaseintheamountofSphagnumsporesrecordedattheendofMIS2,markingthebeginningofthepeatbogformationandtheincreaseofthein-situbiomass.Thesummergreentaxa,whichincreasedduringtheHolocene,mayhavealsocontributedtotheTOCincrease.
2012ElsevierLtdandINQUA.Allrightsreserved.1.IntroductionTheShennongjiamountainrangeincentralChinaisstronglyinfluencedbytheSoutheastAsianMonsoon(SAM),andisanimportantareainsouth-centralChinaintermsofbiodiversity,beingrichintertiaryrelicsandendemicplants(Shenetal.,2005;Weietal.,2010;Lopez-Pujoletal.,2011).TheSAMislinkedtotheannualcycleofsolarenergy,whichproducesextremeseasonalityinwinddirection,rainfallandtemperaturepatternsovertheAsiancontinent(WebsterandChang,1997).ThisclimatesystemhasastrongimpactonthewholeAsiancontinentfromthetropicaltothetemperatezones(Nietal.,1998;Fangetal.,2002;Liuetal.,2010).ClimatechangesthroughouttheQuaternaryinsouthernChinaarecharacterizedbyalternationsofthesummermonsoonstrength(Fig.1A).ThisstudyfocusesonanewsiteintheDajiuhuBasin,oneoftheregion’sbestpreservednationalwetlands,inthewesternShen-nongjiaMountains(Fig.1B).Thickpeatdepositsandapparentlycontinuoussedimentationhasallowedforthereconstructionofpastvegetationandclimatechangesbymeansoffossilpollenanalysis(Lietal.,1992;Liuetal.,2001;Zhangetal.,2002;Zhaoetal.,2007;Shietal.,2008;Zhuetal.,2009).MoststudiesintheregionhavefocusedontheHolocene,althougharecentpollenstudyof3mcorefromDajiuhu,datingbackto16,000calBPhasallowedforreconstructionsofforestdynamicsacrossmuchofthelastglacialeinterglacialtransition(LGIT)(Zhuetal.,2009).Vege-tationresponsesincentralChinaduringthelastglacialperiodarestillpoorlyunderstood(Herzschuh,2006;HarrisonandSanchezGoñi,2010),andoneoftheaimsofthepresentstudyistoaddressthisknowledgegap.2.RegionalsettingThesubtropicalDajiuhupeatbogislocatedat1700ma.s.l.inthewesternShennongjiaMountainswhichbelongtotheeasternextensionofDabaMountainRangesoftheupper-middlereachesofYangtzeRiver,CentralChina(Fig.1A).TheDajiuhuwetlandcoversabout16km2,about50%ofwhichiscoveredwiththickpeat(Zhang,1982)(Fig.2).*Correspondingauthor.E-mailaddress:[e-mail](R.Cheddadi).ContentslistsavailableatSciVerseScienceDirectQuaternaryInternationaljournalhomepage:
2012ElsevierLtdandINQUA.Allrightsreserved.doi:10.1016/j.quaint.2012.01.009QuaternaryInternationalxxx(2012)1e6Pleasecitethisarticleinpressas:Li,J.,etal.,Vegetationchangesduringthepast40,000yearsinCentralChinafromalongfossilrecord,QuaternaryInternational(2012),doi:10.1016/j.quaint.2012.01.009Theregionalclimateischaracterizedbyatransitionbetweensubtropicalandwarmtemperateregimes.Underthestronginflu-enceoftheSAM,theareaismarkedbyshortwarmandwetsummersandlongcolddrywinters.Presentlythemeanannualtemperatureisw7.5
Candannualprecipitationis1550mm,40e50%ofwhichfallsinsummer.Annualevaporationvariesfrom500to800mm,indicatingrelativelyhighhumidity.Climaticconditionsvarystronglyalongtheregion’ssteepalti-tudinalgradients,andtheforestecosystemsshowdistinctbeltswithhighplantdiversityintheShennongjiaMountains(Shenetal.,2005).Withincreasingaltitude,vegetationcommunitiesgradefromevergreenbroadleavedforestthroughtodeciduousbroad-leavedforestandconiferousforest.Thevegetationsurroundingthesiteiscurrentlycharacterizedbytemperatedeciduousandwarmtemperatebroadleavedtrees(Fig.2a),wherethedominanttaxaincludeQuercusoliena,Q.spinosa,Fagusengleriana,F.lucida,Betulaluminifera,Carpinuscodata,Juglanscathayensis,Pterocaryainsigsis,Aceroliverianum,andRhododendronspp.ThelocalshrubsaremostlyCotoneasteracutibolis,Cornusvalteri,andRosaspp.athigheraltitudes,conif