Abstract Pedodiversity in the United States of Ame

PedodiversityintheUnitedStatesofAmericaYinyanGuo,PengGong,RonaldAmundson*DivisionofEcosystemSciencesandCenterforAssessmentandMonitoringofForestandEnvironmentalResources(CAMFER),151HilgardHall,CollegeofNaturalResources,UniversityofCalifornia,Berkeley,CA94720-3110,USAReceived8July2002;accepted17March2003AbstractLittleattentionhasbeenpaidtoanalysesofpedodiversity.Inthisstudy,quantitativeaspectsofpedodiversitywereexploredfortheUSAbasedontheStateSoilGeographicdatabase(STATSGO).First,pedodiversityindicesfortheconterminousUSAwereestimated.Second,taxa–arearelationshipswereinvestigatedineachsoiltaxonomiccategory.Thirdly,differencesinpedodiversitybetweentheUSDA-NRCSgeographicalregionswerecompared.Fourth,thepossiblemechanismsunderlyingtheobservedrelativeabundanceofsoiltaxawereexplored.Resultsshowthatasthetaxonomiccategorydecreasesfromordertoseries,Shannon’sdiversityindexincreasesbecausetaxarichnessincreaseddramatically.Therelationshipbetweenthenumberoftaxa(S)andarea(A)isformulatedasS=cAz.Theexponentzreflectsthetaxa-richnessofsoil‘communities’andincreasesconstantlyastaxonomiccategoriesdecreasefromordertoseries.The‘‘West’’USDA-NRCSgeographicalregionhasthehighestsoiltaxarichness,followedbythe‘‘NorthernPlains’’region.The‘‘SouthCentral’’regionhasthehighesttaxaevenness,whiletaxaevennessinthe‘‘West’’regionisthelowest.The‘‘West’’orthe‘‘SouthCentral’’regionshavethehighestoverallsoildiversityinthefourhighesttaxonomiccategories,whilethe‘‘West’’or‘‘NorthernPlains’’regionshavethehighestdiversityinthetwolowesttaxonomiclevels.Thehighdiversityindexinthe‘‘West’’regionresultsfromhightaxarichnesswhilethehighdiversityindexinthe‘‘SouthCentral’’regionresultsfromanevennessoftaxa.Asthetaxonomicleveldecreases,thepatternoftaxaabundanceapproachesalognormaldistribution.Oneofthekeyfindingsofthisresearchisthatatlowerlevelsofsoiltaxonomicdivisions(especiallytheserieslevel),soiltaxaincreasecontinuouslywithincreasingarea,indicatingconsiderablesoilendemismintheUSA(andlikelyaroundtheworld),akeyconsiderationinconservationandpreservationplanning.D2003PublishedbyElsevierScienceB.V.Keywords:Soil;Soilsurvey;Taxonomicdiversity;Taxa–arearelationships;Abundancemodels1.IntroductionBiodiversityhasbecomeamajortopicinecolog-icalresearchinthepastfewdecades(GastonandSpice,1998).Studiesonbiodiversityhavefocusedontheabovegroundfloraandfauna,thoughinrecentyears,undergroundbiodiversityhasbeenreceivingattention(Copley,2000).However,fewstudieshaveconsideredpedodiversity(i.e.soildiversity),whichisabasisforbeginningtocharacterizeregionalbiodi-versitygiventhestrongrelationshipbetweensoilsandfloraandfauna(Major,1951;Jenny,1980).Thesoilmantlehasthedistinguishingcharacteris-ticofcontinuouschange(variability)inbothhorizon-0016-7061/$-seefrontmatterD2003PublishedbyElsevierScienceB.V.doi:10.1016/S0016-7061(03)00137-X*Correspondingauthor.Fax:[phone].E-mailaddress:[e-mail](R.Amundson).(2003)99–115talandverticaldimensions(MausbachandWilding,1991;MacBratney,1992).Soiltaxonomyisbasedonbreakingthecontinuumintodiscretegeographicalsegmentsofrestrictedrangesinsoilproperties,andthereforeisapotentiallyusefulmeansofisolatingthefeaturesrelevanttosupportingregionalbiodiversity.Studiesontherelationshipbetweenpedodiversityandbiodiversityhavebeenhamperedduetothelimitationofgeo-referencedGISdataforbothpedodiversityandbiodiversityacrosslargegeographicareas.Pedodiver-sitystudieswerefirststartedbyanalyzingsoilseries–arearelationships(BeckettandBie,1978).Theterm‘‘pedodiversity’’wasdevelopedbyMcBratney(1992)whodiscussedlandscapepreservationstrategiesbasedonpedodiversity.Recently,examinationsofpedodi-versityusingindicescommonlyusedtocharacterizebio-diversityhavebeenmade(Iba´n˜ezetal.,1995,1998).Inthesestudies,theFAOsoilmapoftheworldwasusedasthesoildatabase,asystemthatcontainedonly26soiltypesfortheworldwhentheanalysiswasconducted.Thisanalysisrevealedthatpedodiversityinthecontinentsoftheworldwascharacterizedbysimilarity,andthattaxarichnessdidnotincreaseastheareastudiedincreased.Moreresearchonpedodi-versityatfinerscalesofresolutionneedstobecarriedoutinordertobetterunderstandhowsoilresourcesaredistributedgeographically(Yaalon,1998).Generally,therearetwowaystocharacterizebiodiversity:(1)developdiversityindicesand(2)studythepatternsoftherelativeabundanceofspecies.Diversityofacommunitydependsontwocompo-nents:thenumberofspecies(orspeciesrichness)andtheevennessofthespecies—i.e.howtheindividualsareapportionedamongthespeciespresent.Usually,threetypesofbiodiversityindices(richness,evenness,anddiversitytakingbothrichnessandevennessintoaccount)areconsidered.Whileabiodiversityindexcharacterizesthediversityofasampleoracommunitybyasinglenumber,onlyadetailedstudyonthepatternofquantitativeabundancewillrevealthemechanismonhowacommunityisformedorchar-acterized.Manyspeciesabundancemodelshavebeenproposed(MacArthur,1957,1960;Williams,1964;May,1975,1986;Hughes,1986;Tokeshi,1990,1993;Bell,2001),althoughonlyfourmodelshaverepeatedlybeenhighlightedintheecologicalli