LITERATURECITEDRTRBPRIMACK2006TropicalrainforestsWhycrosscontinentalcomparisonsareneededTrendsEcolEvol21104TSHWYUANSGCNKPFL2006MacroscalebirdspeciesrichnesspatternsoftheE ID: 439218
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isanyhopeofstandardization.Iexcludedmarinesystemsbecauseoftheratherdifferentzonationimposedbyphysicaloceanography.IsearchedforarticlespublishedinEnglishsince2000thatusedthetermssubtropicsor(morecommonly)sub-tropicalinthetitle.Initially,Iconnedthesearchtomajorinternationaljournalsinecology(EcologyJournalofEcologylogiaPlantEcology),tropicalecology(BiotropicaJournalofTropicalEcology),biology(AmericanJournalofBotanyJournalofZoologyforestry(ForestEcology&Management),andconservationbiologyConservationBiology,BiologicalConservation,Biodiversity&Conserva-),butIhadtoincludesomepapersfromlowerrankedjournals(allinternationalandwithoutaspecicgeographicalfocus)forareasoftheworldthatwereinadequatelyrepre-sented(10)intheinitialsurvey.Fromeacharticle,Iextractedthelatitudeofthemainstudysite.Wherearangeoflatitudeswasgiven,Itookthemean,asIalsodidformultiplenearbysites,butIexcludedallarticleswherethelatitudinalspreadofsiteswaslarge()orwheretherewasanyambiguityinthedesignationofthesiteassubtropical.Ifound180articlesfrom14countriesthatmetmycriteria:92fromAsia(mostlyChina,followedbyJapanandIndia),34fromSouthAmerica(mostlyArgentinaandBrazil),18fromAus-tralia,13fromtheCaribbean(mostlyPuertoRico),11fromNorthAmerica,10fromSouthAfrica,and2fromtheCanaryIslands.Only18articles(10%)usedsubtropicaltorefertoasitepolewardof30.0,andallthesewereat30.0andreferredtoecosystemsthatoccurredpredominantlybelow30.0.Atotalof26articles(14%)appliedthetermsubtropicaltositeswithinthetropics,buthalfofthesewereintheCaribbean(18.0allbutoneinPuertoRico),threeotherswerealsointheNeo-tropics(19.8),andalltherestwerepolewardof22.0ExceptfortheCaribbean,amajorityofsitesinallregionswereinthelatitudinalbelts23.4fromtheequator.Theoverallmedianwas26.7andtherangeofmediansacrossregionswith10articlesandlandspanningthisbeltwas26.1(SouthAmer-ica)to28.8(SouthAfrica).Reanalysisusingsites(ratherthanarticles(180)asreplicateshadanegligibleeffectonthesenumbers.Thus,currentusageacrossthesubtropicslargely(75.6%ofrecentarticlesstudied)restrictsthistermtothelatitudinalbeltspolewardfromtheTropicsofCancerandCapricornto30.0northandsouth.ThisagreementwassurprisingasIcameacrossnoexplicitdenitionofthesubtropicsthatusedtheselimits.Thecantexceptions()wereallontheequatorwardsideandallreectthelifezonesystemofHoldridge(1978),whichhasbeenwidelyusedintheNeotropics,butrarelyelsewhere.Theoccurrenceinthissystemoflifezoneswellwithinthetropicsseemstobeasimpleconsequenceoftheuseofequallogarithmicdivisionsofthemeanannualbiotemperature,ratherthanareectionofanyfundamentalbiologicalchangeatthethresholdbiotemperatureof24Howcoherentarethesubtropicsifdenedasthelatitudinalbeltsbetween23.4and30.0N/S?Thesetwobeltsaresepa-ratedbythe5185-kmwidthofthetropics,butthisisnomorethanthedistancethatseparatessomemajortropicallandareas(Corlett&Primack2006).Tropicalmontanehabitatsmayhaveactedasbridgesorsteppingstonesacrossthetropicallowlands,mostobviouslyinSouthAmerica.Wheremountainsareabsentormarinebarriersoccur,vertebratefaunasatsimilarlongitudescanbeverydifferentonlythemostmobilegroupsaresharedbetweenhumidsubtropicalAsiaandAustralia,forexampleorasandinvertebratesfaunasaremoresimilar.Theexplosivespeciationoftheplantgenusinboth(northern)subtropicalEastAsiaand(southern)subtropicalSouthAmerica,anditspres-enceinmostothersubtropicalhumidforests,isanexampleofthislatterpattern.Aswiththetropics,thesesimilaritiesanddif-ferencesprovideopportunitiesforintercontinentalcomparisonsthattreatwidelyseparatedareasasnaturalexperimentsintheassemblyofsubtropicalbiotas.Asonemovesawayfromtheborderofthetropics,winterlowtemperaturesdecline,mildfrostsbecomemorefrequent,andtropicalplanttaxaareincreasinglyexcluded.Itistempting,there-fore,toseethesubtropicsasmerelytransitionzonesbetweentropicalandtemperatesystems.Thisview,however,isatleastpartlyanartifactofthecommonandarbitrarydivisionoftaxaintotwotropicalandnon-tropicalandthepatternwouldlookdifferentiftaxathatoccurredpredominantlybetween23.4N/Swereplacedinaseparatecategory.InEastAsia,wherethelandareadeclinestowardtheequator,somehigherleveltaxareachmaximumdiversityinthesubtropics(e.g.,ingbirds;Dingetal.2006).Inanycase,climategradientsinthesubtropicsarenosteeperthaninotherextratropicalregions.Ecologically,thenaturalvegetationofhumidsubtropicalregionsisadistinctivetypeofevergreenbroad-leavedforest,rec-ognizedinmostregionalvegetationclassicationsandwithasimilarstructureinallregions(pers.obs.).AtleastinEastAsia,theseforestsmaintainhighratesofphotosyntheticactivityyear-round(Tanetal.2012),unlikeforestsfurtherpolewards.Aridandsemi-aridecosystemsinthisbeltvarygreatlybetweenregionsintheiroristics,butawaitaglobalcomparisonoftheirstructureandfunction.Iconcludethatweshouldrestricttheuseofthetermtothelatitudinalbeltbetween23.4and30.0,atleastintitles,abstracts,keywords,andglobalcomparisons.Thechoiceofisarbitrary,butconvenientandalreadyconventional.Aswiththeterm,itwouldbereasonabletoallowtheuseoftheadjectivaltorefertoclimates,ecosystems,orspeciesthatoccurpredominantlywithinthesubtropics,butmayextendafewdegreesaboveorbelowthisbelt.Wherewidelyusedregionalvegetationorclimateclassicationsystems,suchasthoseofHoldridgeandKoppen-Geigerdiscussedabove,incor-porateadifferentusageofthetermsubtropical,anexplicitdis-tinctionshouldbemadeinthetextbetweenthevegetationorclimatetypeandthelatitudinalbelt.ACKNOWLEDGMENTSIamgratefultoDavidDudgeonandFerrySlikforusefuldiscus-sionsandtotwoanonymousreviewersfortheirhelpfulsugges-tions.2Corlett LITERATURECITED,R.T.,R.B.PRIMACK.2006.Tropicalrainforests:Whycross-continentalcomparisonsareneeded.TrendsEcol.Evol.21:104,T.S.,H.W.YUAN,S.G,C.N.KP.F.L.2006.Macro-scalebirdspeciesrichnesspatternsoftheEastAsianmainlandandislands:Energy,areaandisolation.J.Biogeogr.33:683OMROES,M.2003.ClimatologicalcharacteristicsofthetropicsinChina:ClimateclassicationschemesbetweenGermanscientistsandHuangBingwei.J.Geogr.Sci.13:271,J.F.1976.Appliedclimatology,anintroduction,secondedition.OxfordUniversityPress,Oxford,UK.,L.R.1978.Lifezoneecology.IICA,TropicalScienceCenter,SanJosedeCostaRica.,W.M.,M.M.KAUFMAN.2012.Physicalgeography:Greatsystemsandglobalenvironments.CambridgeUniversityPress,Cambridge,,M.C.,B.L.FINLAYSONT.A.M.2007.UpdatedworldmapoftheKoppen-Geigerclimateclassication.Hydrol.EarthSyst.Sci.11:1633,J.F.,L.M.TRAPASSOR.E.G.2010.Fundamentalsofphysicalgeography.ThomsonBrooks/Cole,Belmont,CA.,Z.H.,Y.P.Z,N.L,Y.J.H,Y.J.Z,G.Y.Z,Y.L.,J.Y.JUANG,H.S.C,J.H.Y,G.R.Y,X.M.S,Q.H.,K.F.C,D.A.SY.H.L.2012.Anobserva-tionalstudyofthecarbon-sinkstrengthofEastAsiansubtropicalevergreenforests.Environ.Res.Lett.7:044017.REWARTHA,G.T.1968.Anintroductiontoclimate.McGraw-Hill,NewYork.WherearetheSubtropics?3