White sand vegetation of brazilian amazonia


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White sand vegetation of brazilian amazonia

  1. 1. White-Sand Vegetation of Brazilian Amazonia Author(s): Anthony B. Anderson Source: Biotropica, Vol. 13, No. 3 (Sep., 1981), pp. 199-210 Published by: The Association for Tropical Biology and Conservation Stable URL: http://www.jstor.org/stable/2388125 . Accessed: 02/06/2011 15:17 Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp. JSTOR's Terms and Conditions of Use provides, in part, that unless you have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and you may use content in the JSTOR archive only for your personal, non-commercial use. Please contact the publisher regarding any further use of this work. Publisher contact information may be obtained at . http://www.jstor.org/action/showPublisher?publisherCode=tropbio. . Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printed page of such transmission. JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. The Association for Tropical Biology and Conservation is collaborating with JSTOR to digitize, preserve and extend access to Biotropica. http://www.jstor.org
  2. 2. White-Sand Vegetation of Brazilian Amazonia AnthonyB. Anderson1 InstitutoNacional de Pesquisas da Amazonia (INPA). Caixa Postal 478, 69.00 Manaus. AM. Brasil ABSTRACT This paper describesa distinctivevegetationtypeoccurringon white-sandsoils whichare scatteredthroughoutthe Amazon region.AlthoughessentiallyhomologousthroughoutAmazonia,white-sandvegetationis knownlocallybyvariousterms:to avoid confusion,exclusiveuse of the singleterm"Amazon caatinga" is proposed. The Amazon caatinga is distinguished fromotherregionalvegetationtypesby itswhite-sandsoil, scleromorphicphysiognomy,and unusual floristiccomposition. Possible originsof the white-sandsoil include: in-situ weathering,alluvial deposition,or podzolization.The scleromorphic physiognomyof the caatinga indicatesa lack of nutrientsand/or periodicwaterdeficienciesin the soil. Extremeedaphic conditionsand the insularityof thesesiteshave probablyacted as powerfulselectiveforces,generatinga biota character- isticallylow in diversityand high in endemism.Numerousendemic species may currentlyface extinctiondue to wide- spread burningof caatingavegetation.Repeated fireson white-sandsitesresultin the effectivearrestof succession;subse- quent miningof thesesitesforsand eliminatesany possibilityof vegetationalreestablishment.Alternativebenefitsof the Amazon caatingain its intactstateare considered. RESUMO Este trabalhodescreveum tipo distintode vegetacAoque ocorreem solos de areia brancaespalhadospela regiao amazonica. Apesar de ser essencialmentehomologo em toda a Amazonia, esse tipo vegetacionale' conhecido localmentepor varios termos:para evitarconfusao,o uso exclusivodo termo"caatingaamazonica"e proposto.A caatingaamazonicase distingue de outrostipos regionaisde vegetacaopor seu solo de areia branca,sua fisiognomiaescleromorfica,e sua raracomposicio floristica.As possiveisorigensdo solo de areia branca incluem: intemperismoin situ,deposicao aluvial,ou podzolizacAo. A fisiognomiaescleromorficada caatingaindica uma faltade nutrientese/ou periodicasdeficienciasde agua no solo. Ex- tremascondices edaificase a insularidadedesses sitiosprovavelmentetematuadocomopoderososfatoresseletivos,gerando uma biota caracteristicamentepobre em diversidadee rica em endemismo.Especiesendemicasestao em perigode extinco devidoa queimada da caatinganas areas da Amazonia em desenvolvimento.Repetidas queimas desta vegetacao efetiva- menteimpedema sucess-ao;a extraao de areia para construcoeselimina qualquer possibilidadede re-estabelecimentovege- tacional. Os beneficiosda preservacdoida caatinga amazonicaem seu estado naturalsio considerados. SOILS COMPOSED ENTIRELY OF WHITE SAND are scatteredthroughoutthe Amazon region of Brazil. Associated with these soils is a highly distinctive vegetation,which ranges in structurefromsavanna to forestand is characterizedby pronouncedsclero- phylly,low diversity,and high endemism.Due to its distinctivenessand relative simplicity,white-sand vegetation has been the subject of considerable scrutinyby botanists.Yet observationsand studiesin differentareas of Amazonia have produced a frag- mented knowledge of this vegetation,as well as a confusingarrayof termsto describe it. Mounting pressuresfordevelopmentof the regionincreasethe need forinformationconcerningvegetationon oligo- trophicsoils, which have exceptionallylow agricul- tural po-tential.With the objective of developing a more syntheticterminologyand vision, this paper examinesgeneralaspectsof white-sandvegetationin Brazilian Amazonia. TERMINOLOGY Evergreensclerophyllousvegetationon whitesand is lPresent address: Department of Botany, Universityof Florida,Gainesville,Florida 32611, U.S.A. recognizedbydistinctvernaculartermsineachcoun- tryor regionwhereit occurs(table 1). Suchterms continueto appearin theliterature,despiteBeard's (1955) attempttoestablisha universalterminology. In Brazil,however,thereis evendisagreementover whichvernaculartermor termsshouldbe utilized. Spruce(1908) firstused thetermcaatingato de- scribe the vegetationunder consideration.Later, Ducke (1922) andSampaio(1945) referredtodif- ferentstructuralphasesofthisvegetationas campina and campinarana.Otherauthorscitetermssuchas humirizal,carrascal,chavascal,and charavascal(Au- breville1961,Pires1974). In thebotanicalliteratureon BrazilianAmazonia, thetermsmostcommonlyencounteredarecaatinga, campina,andcampinarana.As caatingaalsorefersto a totallyunrelatedvegetationtypeinthearidNorth- eastof Brazil,Takeuchi(1960) suggestedthatthe termnotbe appliedin Amazonia,and subsequent authorshaveconcurred.Buttheyhavenotagreedon whichtermsshouldtake its place: Pires (1974) usedtheterms"lowcampina"(campinabaixa) and "high campina" (campina alta), Lisboa (1975) proposed"Amazoncampina"(campinaamazonica) and "Amazoncampinarana"(campinaranaamazon- BIOTROPICA 13(3): 199-210 1981 199
  3. 3. TABLE 1. Vernaculartermsfor evergreensclerophyllousvegetationon white-sandsoils in the humidtropics. TERMS campina caatingabaixa muribush bana varillal bajo padang campinarana caatingaalta wallaba forest cunuri varillal alto kerangas yaguacanan REGION CentralAmazonia NorthwestAmazonia Guyana Venezuela Peru Borneo (Brazil) (Brazil) SOURCE Ducke & Black Spruce (1908) Richards Herrera Revilla Whitmore (1953) Rodrigues (1961) (1952) (1977) (1978) (1975) ica), and botanists of the Projeto Radambrasil (1976) used the single term "campinarana" with variousdescriptiveepithets. The present proliferationof terms obscures a generalconsensusthat,despitestructuraland floristic variations,the vegetation under considerationrep- resentsa continuumwith manyfeaturesin common. To resolve the confusionover terminology,each of thetermsmostprevalentin theliteratureis reviewed. CAMPINA.-This termis used in Amazonia to refer to savannas and scrubson white sand (Ducke and Black 1953); it is also used in otherregionsof Bra- zil to describestructuralphasesof cerradoand campo (G. Eiten, pers. comm.). In Amazonia the term campina,'meaning "small field," appropriatelyde- scribesreducedphasesof thevegetationunderconsid- eration,which typicallyoccupy small and disjunct areas over much of the region.The chiefdisadvant- age of campina is that it requires anothertermto describe the less-reducedphases,which range from low to moderatelytall forests. CAMPINARANA.-The meaningof thisterm,'false campina,"provideslittleor no descriptiveinforma- tion,and its applicationis confusing.Local inhabit- antsof centralAmazonia,wherethetermoriginated, use it to referto a varietyof upland vegetationtypes of soils witha highpercentageof sand.For example, non-sclerophyllousforestson sandyoxisols,whichare high in diversityand low in endemism,are called campinarana: such forestsbear no relation to the vegetation under consideration.Ducke and Black (1953) vaguelyused the termto referto a "transi- tional" vegetationbetween savannas and forestsin Amazonia. Botanists of the Projeto Radambrasil (1976) used the term (with various epithets) to describe sclerophyllousvegetation on white sand, non-sclerophyllousupland forestson sandy oxisols, and palm swamps on sandyalluvium.The value of the term campinarana is thereforereduced by its imprecisemeaningand variableapplication. CAATINGA.-This term is derived from the Tupi language: "caa" means leaf, tree,or forest;"tinga" meanswhite (Rodrigues1961), possiblyin refer- enceto therelativelyhighlight-penetrationcharac- teristicof white-sandvegetation.Caatingahas been usedbylocal inhabitantsand botanistsaliketo de- scribesuch vegetationin the Rio Negro region. Hence the termis etymologicallyappropriateand, withinAmazonia,unambiguousin itsapplication. To undersco,retherelatednessofwhite-sandveg- etationin BrazilianAmazonia,it is proposedthat the termcaatingabe applied to this vegetation throughouttheregion.Withdescriptiveepithets,the singletermcan be used to referto all structural phasesofthisvegetation.To preventconfusionwhen consideringotherphytogeographicregionssuch as theNortheastofBrazil,theterm"Amazoncaatinga" is recommended(cf.Ducke and Black 1953). This termis alreadyacceptedbyphytogeographersinBra- zil (e.g.,Eiten1978; J.M. Piers,pers.comm.)and has gainedacceptanceabroad (e.g., Sarmientoand Monasterio1975,Klingeet al. 1978). DELIMITATION VegetationtypeshomologoustotheAmazoncaatinga havea worldwidedistributionin thehumidtropics (cf. Whitmore1975). In northernSouthAmerica, theyare reportedin FrenchGuiana (Granville,in press),Surinam(Heyligers1963), Guyana(Rich- ards 1952, Fanshawe1952), and the Amazonian portionsof Venezuela (Beard 1955, Klinge et al. 1978), Colombia(R. E. Schultes,pers.comm.),and Peru (Revilla 1978). In Brazil,caatingais one of themajorvegetationtypesofAmazonia(Pires1974) andoccursthroughouttheregion(Ducke andBlack 1953,Aubreville1961,Sombroek1966), generally occupyingsmalland disjunctareas (fig. 1). How- ever,in theRio Negroand Rio,BrancoBasinsof northwesternAmazonia,caatingacovershundreds of thousandsof squarekilometers(ProjetoRadam- brasil1976; J. M. Pires,pers.comm.). It is not knowntooccurinotherregionsofBrazil,apparently reachingitssouthernmostextensionatapproximately Lat.8-9?S (Soares1953,LlerasandKirkbride1978). Caatingais limitedto soilscomposedentirelyof 200 Anderson
  4. 4. FIGURE 1. Aerial view of a caatingascrubin centralAma- zonia. Total area of the caatinga scrub is approximately1 hectare; the surroundingcaatinga woodland occupies an area of less than 50 hectares. white sand. Where these sands grade into soils con- taining even a small percentage (< 5%) of clay withinthereachof roots,caatingagives way to other vegetationtypes,suchas non-sclerophyllousforestsor floristicallydistinctcampos.While caatingagenerally occurs on topographicallyintermediateto high sites (the so-called terrafirme), it is also found on low sites which are subject to flooding. Even on terra firme,caatinga soils may be hydromorphic,due to local drainage patternsor the presenceof an under- lying hardpan (Viera and Oliveira 1962). Other sclerophyllousvegetationtypesof Amazonia, which have similaritiesand in some cases forma continuum with the caatinga,are as follows. RESTINGA.-This vegetation type occurs on sand dunes adjacent to the Atlantic coast of Amazonia, extending south to Rio de Janeiro.Although phy- siognomicallysimilarto reducedphases of the Ama- zon caatinga,thetwovegetationtypesare floristically unrelated (Pires 1974). AMAZONIAN CAMPO.-This vegetation type has a widespreaddistributionin Amazonia and is extreme- ly heterogeneous (Egler 1960, Pires 1974, Eiten 1978). In comparisonto caatinga,firetypicallyplays a more prominentrole in campo, and many of its component species (e.g., Curatella americana) are fire-resistant.Campo is best distinguished from caatinga by its soils, which generallycontain var- iableamountsofclay,anditsrelativelycosmopolitan flora.Yet gradationsoccurbetweenthe two veg- etationtypes.For example,a floristicallyintermed- iatevegetationis reportedon redsandsin Surinam (Heyligers1963) and southernAmazonia (Lleras andKirkbride1978). A curioustypeof campo,knownas camporup- estre ('"rockcampo"), has manysimilaritieswith the vegetationunderconsideration.In Amazonia, camporupestreis mostlyrestrictedtotheperipheries of theregionand occurson rockyoutcropswhich oftengrade into sandysoils. Althoughtheirsub- stratesform a continuum,campo rupestreand caatingahave distinctphysiognomicand floristic characteristics.The herbs,shrubs,and small trees of campo rupestrefrequentlyhave whorledleaves and candelabra-likebranching(Eiten 1978), totally unlikegrowthformsin caatinga.Althoughboth vegetationtypeshave commonfloristicelements, campo rupestrehas manyunusualspeciesand an evenhigherdegreeof endemism. IGAPO.-This type,oftenassociatedwithsandysoils, occursin inundatedareas adjacentto streamsand riversthroughoutAmazonia(Pires 1974). Its rela- tivelylowtopographicpositionandmorecosmopoli- tanflorabestdistinguishigap6fromcaatinga.How- ever,bothvegetationtypesforma continuum,with numerousphysiognomicand floristicsimilarities. Likecaatinga,igapois drainedbytea-coloredwater, whichformstheblack-waterstreamsandriverschar- acteristicof the region (cf. Klinge 1967, Janzen 1974). Althoughprecisedelimitationis notalwayspos- sible,the highlycharacteristicsoils,physiognomy, and floraof thecaatingamakeit one of themost distinctivevegetationtypesof Amazonia.Theseas- pectswillnowbe examinedin greaterdetail. STRUCTURAL AND FUNCTIONAL ASPECTS STRUCTURE AND PHYSIOGNOMY ThevariousstructuralphasesoftheAmazoncaatinga can be convenientlyrecognizedas follows(fig.2). CAATINGA SAVANNA (caatinga savanica).-This phaseis dominatedbylichensandgraminoids,which generallyforma sparsecoverover the bare sand. Occasionalclustersof woodyplantsmaybe present, buttheyconstitutea coverof lessthan10 percent. CAATINGA SCRUB (caatingaarbustiva).-This phase is characterizedbyopenareasof baresandandher- baceousplants,intermixedwith shrubsand small treesup to approximately7 m tall.The lattermay White-Sand Vegetation of Amazonia 201
  5. 5. 35 HIGHFORESTONOXISOL CAATINGAFOREST 'E~~~~~~~~~~~~~~~~~~~~~~~~~~~" 0O 25 50 7514 15 CAATINGAWOODLAND CAATINGASCRUB 0 ~~~~~~25 50 '5 ItETERS FIGURE 2. Profiles of oxisol forestand caatinga forest, woodland,and scrub.Upper profilefromupper Rio Negro (Rodrigues 1961); lower profile from central Amazonia (Anderson 1978). Depths of upper and lower profilesare 5 m and 2 m, respectively. formdistinctiveclumpsor be distributedsingly, formingup to 90 percentcover(fig.3). CAATINGA WOODLAND (caatinga arb6rea).-This phasehasa moreor lesscontinuouscoverof shrubs and trees.The canopyis oftenpatchyand variable in height,rangingfromapproximately5 to 15 m, withoccasionalemergentsto20 m.Lightpenetration is high,permittinga denseunderstoryofshrubsand small treeswith thin trunks(fig. 4). CAATINGAFOREST (caatingaalta).-Here thecan- opy,whichreachesheightsof 20 to almost30 m,is generallyuniformandcontinuous.Lowerstratatend toforma patchycover,whichpermitsrelativelyhigh lightpenetration. Althoughextremelyvariable,thestructuralphases oftheAmazoncaatingaconstitutea continuum,with a numberofcharacteristicsin common.All aremore or lessreducedin biomassand haverelativelyhigh lightpenetration.Elementstypicalof tropicalrain forests-suchas drip-tips,treebuttresses,vines,and big woody climbers-are relativelyinfrequentor absent.Epiphyticorchids(cf. P. I. S. Braga1977), bromeliads(cf. M. M. N. Braga 1977), and bryo- phytes(cf. Lisb6a 1976) are oftenabundantand highin diversity.Wherewoodyplantspredominate, thecaatingamaybe characterizedbythickaccumu- lationsofhumusandlitter(cf.Stark1970,Anderson etal. 1975), whichareseldomencounteredelsewhere in thehumid,lowlandtropics. The physiognomyof caatingaplantsis likewise distinctive,witha numberof characteristicswhich suggestphysiologicalstress.Shrubsand smalltrees typicallyhave a dwarfedand rachiticaspect,with reducedquantitiesof foliage,thin branches,and smallcrowns;occasionalemergentsmayhaveexcep- tionallywidespread,twistedbranches(fig.5). Stump FIGURE 3. Panoramaof a caatingascrub.ReservaBiologica do INPA/SUFRAMA, BR-174 km 45. r _a FIGURE 4. View of a caatingawoodland.ReservaBiol6gica do INPA/SUFRAMA, BR-174 km 45. sproutingis commonin the caatinga,especiallyin structurallyreducedphases.Althoughsuchfeatures are characteristicof vegetationwhichis periodically burned,otherfire-adaptivefeaturesareabsent:bark is thinand smooth,themajorityof species(includ- 202 Anderson
  6. 6. 7~~~~~~~7,~~~~~~~~I FIGURE 5. Branchingof Aldina heterophylla(Legumino- sae), a commondominantof caatinga woodland and scrub in central Amazonia. Reserva Biologica do INPA/SUF- RAMA, BR-174 km 45. ingherbs)areperennial,andvirtuallyall speciesare evergreen.The woody vegetationis distinctively sclerophyllous,withrelativelysmall,shiny,coriaceous leaveswhichareoftenhelderect(fig.6). NUTRIENT DEFICIENCIES The curiousstructureand physiognomyof thecaa- tingaarea reflectionof extremeedaphicconditions, whichmayresultfroma lack of nutrientsand/or periodicwaterdeficienciesin the sandysoils.Pro- ponentsof nutrientdeficienciesas the principal limitingfactor(e.g., Richards1952, Stark 1971, Janzen1974) emphasizethe extremepovertyof soils associatedwiththe caatingaand homologous vegetationtypes:thesesoilsaredeficientin mineral elementsand have an exceptionallylow cationex- changecapacityin comparisionto the morewide- spreadoxisols(table2). The oligotrophicnatureof TABLE 2. Mineral soil propertiesof a non-hydromorphic, white-sandentisol (Manaus-Boa Vista high- way,km 45) and a fine-textured,yellow oxisol (Manaus-Itacoatiara highway,km 30) in cen- tral Amazonia. Data presented:mean+ stand- ard deviation,withnumberofcompositesamples in parentheses.Samnpletakenat 0-10 cm. Property Entisol Oxisol pH 4.7 ?0.4 (15) 4.4 ?0.2 ( 7) C (%) 0.76 0.28 ( 5) 2.26 0.28 ( 6) N (%) 0.03 0.01 ( 5) 0.25 ?0.01 (10) P in ppm 2 ? 1 (10) 4 ? 2 ( 7) CEC in meq/100 g 1.98 ? 1.37( 5) 8.49 ? 4.13( 7) Ca in meq/100 g 0.02 ? 0.01 ( 5) 0.1 ? 0.2 ( 7) K in meq/100 g 0.05 ? 0.03 (15) 0.08 ? 0.03 ( 7) Mg in meq/100 g 0.03 ? 0.01 ( 5) 0.4 ? 0.3 ( 7) Al in meq/100 g 0.6 ? 0.3 (15) 1.6 ? 0.2 ( 7) Base saturation (%) 7 ?3 ( 5) 7.7 ?3.3 ( 6) FIGURE6. Sclerophyllyin Pagameaduckei(Rubiaceae),a commonspeciesofcaatingawoodlandandscrubin central Amazonia.ReservaBiologicado INPA/SUFRAMA,BR- 174 km45. thesesoilsis largelydue to theirorigins,whichmay include:in situ weatheringof impoverishedparent materials,suchas sandstones,quartzites,or granites; alluvialdepositionof quartzsandsoriginatingfrom theGuianaor BrazilianShield;orpodzolizationdue to a fluctuatingwatertablewhichleachesorganic matterandclayconstituents(sesquioxides)fromthe upperprofile,leavingbehinddegradedsand.Tenta- tive nomenclatureand specificexamplesof white- sand soils originatingby theseprocessesare sum- marizedin table3. The leavesof tropicalwhite-sandvegetationex- hibitfeatureswhichappearto be responsesoradap- tationsto nutrient-poorsoils.Foliagein theAmazon caatingais commonlyyellowor chlorotic,yetwith- outsignsofpathogenicinfection,whichmayindicate a widespreadresponseto nutrientdeficienciesin these habitats.Ferri (1960) suggestedthat the coriaceousnatureof leavesin the caatingais due to a low supplyof mineralnutrientsin thesoil; a similar case of scleromorphisminduced by a lack of nutrientshas beendocumentedin thecerradoof centralBrazil (Arens 1963,Goodland1971). Jan- zen (1974) predictedthatleavesof tropicalwhite- sand vegetationcontainexceptionallyhigh levels of phenolicsand othersecondarycompounds.This predictionhas been substantiatedby evidencefrom Africa(McKeyetal. 1978). As a causalmechanism, janzen (1974) hypothesizedthatplantsgrowingon White-Sand Vegetation of Amazonia 203
  7. 7. TABLE 3. Tentativesummaryof the major soil typesassociatedwithcaatingavegetationin BrazilianAmazonia. Nomen- claturefollowsSoil SurveyStaff(1975). Order Suborder Origin Example Source Weatheringin situ of par- Serrado Cachimbo Soares (1953) ent material Entisols Aquents, Psamments Fluvial transport& deposi- Manaus G. Ranzani (pers. comm.) tion Spodosols Aquods, Humods Podzolization S. Paulo de Olivenca Sioli & Klinge (1961) poorsoilsare underincreasedselectivepressureto evolve anti-herbivoredefenses.Yet Davies et al. (1964) showedthatplantsgrownin nitrogen-or phosphorous-deficientsoils producehigherconcen- trationsof phenolicsthanwheflgrownin non-defi- cientsoils.Thisfindingsuggeststhatincreasedoccur- renceof secondarycompoundsin white-sandvege- tationmaysimplyrepresentanacclimationalresponse (St.JohnandAnderson,inpress). The oligotrophicnatureof white-sandsoilshas pronouncedeffectson nutrientcycling.Thick ac- cumulationsof slowlydecomposinglitterprovide an exclusivesubstratefordevelopmentof a rootmat, which hardlypenetratesthe mineralsoil and can be pulled offthe surfacelike a rug. Release of a biotic compound such as ethyleneor an auxin in decom- posing litterhas been shown to induce root growth (St. Johnand Machado 1978). The root mat con- sequentlyattainsa pronounceddevelopmentin trop- ical white-sand vegetation. Klinge and Herrera (1977) foundthatrootsmay compriseover 60 per- cent of the totalbiomass of an Amazon caatinga; in oxisol forests,the figureis typically20 percent.The root mat in white-sandforestsand woodlands is usually 10-30 cm thick, significantly(P -- 0.01) thickerthan its counterparton oxisols,accordingto data fromStarkand Jordan (1978). The thickness of therootmat,combinedwithan exceptionalabun- dance of vesicular-arbuscular(T. V. St. John,pers. comm.) and ectomycorrhizae(Singer 1979), results in increasedabsorbingsurfaceswhich maximize nu- trientuptake.Radio-tracerexperimentsby Starkand Jordan (1978) in white-sandforestin Venezuela demonstratedtheeffectivenessof therootmatin pre- ventingnutrientlosses. Hence, althoughmineraliza- tion of litteris slow,the high area of absorbingsur- facesin the rootmat increasesnutrientuptakewhile minimizinglosses throughthe porous soil. By pro- viding a circuit for increased nutrientuptake and leak-freecycling,the thickrootmat appears to be a key factorin enabling forestsof moderatelyhigh biomassto developon soilswhicharevirtuallysterile. WATER DEFICIENCIES Proponents of water deficiencies as the principal limiting factor would argue that the pronounced scleromorphismof the caatinga representsa xero- morphicresponseto physiologicaldrought.Reduced phases of white-sandvegetationare characterizedby comparativelyhigh surface temperaturesand low relative humidityduring the day (Schulz 1960), which may contribute to soil-moisture deficits through increased evaporation. Excessive drainage throughthe porous sands may periodicallyresultin a drop of the water table below the zone of root penetration (cf. Sioli 1960, Sombroek 1966). The unstable nature of the water table in caatinga has been noted in the upper Rio Negro region,where rainfallis exceptionallyhigh throughoutthe year: a few days without rain can cause dramatic fluc- tuations (E. Medina, pers. comm.). In this same region,Ferri (1960) found a lack of water stress in the leaves of caatinga plants and concluded that waterdeficienciesare not a limitingfactorin these habitats.However, his conclusion was based on a fewdaysofmeasurementscarriedoutduringtherainy season; shortperiodsof waterstressduringthe drier monthsmay be sufficientto exerta controllingin- fluenceon thevegetation(E. Medina, pers.comm.). Working in homologousvegetationin Sarawak, Brunig (1970) found a number of characteristics which appear to have adaptive value by enhancing the cooling of leaves, therebyminimizingtranspira- tion losses necessaryto keep leaves cool. These char- acteristicsinclude: small leaf sizes, which increase convectionalcooling; shinyleaf surfaces,which re- duce heat load by increasingthereflectanceof radia- tion; steep inclinationof leaves,which reducesheat load from incident radiation; and lack of canopy roughness,which reduces heat load by decreasing the interceptionof incidentradiation.In comparison with othervegetationtypes,the Amazon caatinga is also characterizedby relativelysmall leaves, shiny leaf surfaces,steep inclinationof leaves,and lack of canopy roughness: these featuresmay have similar 204 Anderson
  8. 8. adaptivevalue in minimizingtranspirationlosses (cf.Medinaetal. 1978). Presentlackof experimentalevidencemakesit impossibleto determinetherelativeimportanceof nutrientand waterdeficienciesin theAmazoncaa- tinga.Althoughtheirrelativeimportanceremains uncertain,thesedeficienciesappearto be consider- ablygreaterin the caatingathanin othervegeta- tiontypesof theAmazonregion.Undersuchdis- tinctiveselectiveforces,it is no surprisethatthe caatingaisuniquenotonlyinstructuralandfunction- al terms,butin itsbiologicalcompositionas well. BIOGEOGRAPHY The unusualfloraof theAmazoncaatingahas long beennotedbybotanists(e.g.,Spruce1908). Studies of thisvegetationin differentregions(cf. Egler 1960, Rodrigues1961, Piresand Rodrigues1964, Andersonetal. 1975) providesomegeneralinsights concerningtheirfloristicco'mposition.Familiesdom- inantin caatingaforestand woodlandincludeLe- guminosae, Euphorbiaceae, Sapotaceae, Guttiferae, Rubiaceae, and Myristicaceae.Important,high-diver- sitycomponentsof forestson oxisols-such as Mor- aceae, Lecythidaceae,and Loganiaceae (Strychnos) -are absent or extremelyrare in caatinga, while palms may be locally abundant but are invariably low in diversity.Examples of dominantfamiliesin structurallyreduced phases are Melastomataceae, Rubiaceae, Chrysobalanaceae,Myrtaceae,Malphigia- ceae,and Vochysiaceae.Terrestrialherbaceousfamilies include Cyperaceae,Gramineae,Eriocaulaceae,Xyri- daceae, and Schizaeaceae; Cyperaceaeare moreabun- dantthanGramineae,in contrastto mostAmazonian campos (except campo rupestre).Lichens (Cladonia spp.,Parmelia spp.) are a common featurein struc- turallyreduced caatinga. Families of the caatinga whichrarelyoccur in otherlowland vegetationtypes of Amazonia include Cyrillaceae,Ericaceae,and Lis- socarpaceae. Ducke and Black (1953) provided an exhaus- tivelistof specieswhichoccurexclusivelyin caatinga and are endemicto specificregions,suchas theupper Rio Negro. Due to a high incidence of endemic sp-ecies,the floristiccompositionof this vegetation varies considerablyfromone region to another,as indicated by comparisonsbetween distant caatinga sites (Anderson 1978). Yet a numberof species ex- clusive to caatingahave wide geographicrangesand hence serve as indicators of this vegetation over largeareas of Amazonia. Examples include: Cephalo- stemongracile (Rapateaceae), an herb common on humid sites in easternAmazonia: Gaylussacia anma- zonica (Ericaceae), a low shrubwidespreadthrough- out easternand centralAmazonia; Glycoxylonino- phyllum (Sapotaceae) and Pagamea duckei (Ru- biaceae), shrubsor small trees often dominant on caatinga sites in centralAmazonia; Mauritia carana (Palmae), a large palm characteristicof hydro- morphic white sands throughoutthe Rio Negro Basin; Lissocarpa benthami(Lissocarpaceae), Hevea paucifloravar.coriacea (Euphorbiaceae), and Laden- bergiaaomazonensis(Rubiaceae), treespecies typical of caatinga sites in westernAmazonia (Ducke and Black 1953). Many plant species in the caatinga are restricted to a limited range of habitats. Anderson (1978) found that the majority (54.5 %) of vascular ter- restrialspecies in a centralAmazon caatinga occur exclusivelyin thisvegetationtype.A moderatepro- portionof the species also occurs in upland forests on oxisols (23.6%) and igapo (20.0%), which are generallyoligotrophichabitats;relativelyfew (2.6% ) are known fromthe nutrient-richvarzea, a vegeta- tion type located adjacent to white-waterrivers. While the habitatrange of terrestrialspecies tends to be narrow,epiphytessuch as orchids generally occur in a wide range of habitats (P. I. S. Braga, pers. comm.), probablybecause theyare not limited directlyby soil conditions. Although the caatinga has been less studied by zoologists,a numberof animals are presentlyknown to be restrictedto these habitats.A species of titi monkey endemic to western Amazonia, Callicebus torquatus,is foundalmostexclusivelyon white-sand sites (Kinzey and Gentry1979). Two bird species, Neopelma chrysocephalumand Xenopipo atronitens (Pipridae), are limited to white-sandvegetationin Brazil and Venezuela (D. Oren, pers. comm.). In central Amazonia, Brown and Benson (1977) re- portedtwo endemicsubspeciesof the passion flower butterfly,Heliconius hermathena (Heliconiini), which are restrictedto caatinga. Plant communitiesin the caatinga have a com- parativelyreduced species richness (fig. 7), with a pronouncedtendencytoward dominance by one of a fewspecies (Takeuchi 1960,Andersonet al. 1975). Animal communitiesshow a similartrend (cf. Jan- zen 1974). In caatingawoodlandand scrubin central Amazonia, avifaunal diversityas measured by the informationindex value (in ln) was approximately 2.3, compared to values rangingfrom3.5 to nearly 4.0 in adjacentforeston oxisol; thedominantspecies on the caatinga site comprised almost 40 percent of the individualssampled (D. Oren, pers. comm.). Low diversityis probablyin part a functionof in- sularity,as well as of extremeenvironmentalcondi- White-Sand Vegetation of Amazonia 205
  9. 9. 200 0JHigh forest EN Igapo forest g Caatinga woodland 150 w 0 w a- o 100 w z 50- 0 FIGURE 7. Number of species per hectarein Amazonian vegetationtypes.DBH - 10 cm,exceptforsitecorrespond- ing to leftmostbar, whereDBH - 15 cm. Data forleft- most bar fromPrance et al. (1976), formiddle two bars fromBlack et al. (1950), and forrightmostbar fromAn- derson (unpublished data). tions. In centralAmazonia, where the caatinga has a scatteredoccurrence (fig. 8), species richnessis low comparedto the upper Rio Negro region,where this vegetationcovers immense areas (Ducke and Black 1953). Biogeographers(MacArthurand Wil- son 1967) have shownthatarea and degreeof isola- tionaccountformostof thevariationin speciesnum- berson islands: a similarrelationshipappears to ex- ist in thecaatinga. Area and degree of isolationlikewise appear to influencethebiologicalcompositionof thesehabitats. On scatteredcaatinga sites occupying small areas ( < 100 ha), most of the avifauna is comprisedof generalistspecies with a wide geographic distribu- tion; extensivecaatinga sites ( > 100 ha) contain numerous habitat specialists with restrictedgeo- graphic ranges (Oren, in press). As is the case on islands, small and/or isolated caatinga sites appear to select forplant species with long-distancedisper- sal mechanisms(cf. Macedo and Prance 1977). In a caatingain centralAmazonia,Macedo (1977) found that75.7 percentof thespecies investigatedhave the potential for long-distancedispersal,including 59.5 percentwhich are bird-dispersed.Floristiccompari- sons by Anderson (1978) of threecaatinga sites in centralAmazonia revealed a high overlap of genera and species,indicatingthe effectivenessof dispersal mechanismsover long distancesand formidablebar- rierssuchas theRio Negro. 2'30 KM-50 ~ZF- I KM-40 240 0 1 2 3 LEGEND SCALE I 125 000 KM 0 CAATINGA (Scrub or savanna pkem) FIGURE 8. Occurrenceof caatingasavannaand scrubin an area of centralAmazonia. The insularnatureof thecaatingahas furthersig- nificancein rapidlydevelopingareas suchas Manaus, where this vegetationis systematicallyburned (fig. 9). At burned sites,manyspecies and certainchar- acteristicelements of the original flora-such as lichens,bryophytes,bromeliads,and orchids- disap- pear completelyand are replaced by a monotonous secondarygrowth known as capoeira (Ducke and Black 1953, Anderson 1978). As caatinga vegeta- tion is rapidlydestroyedover widerareas,recoloniza- tion by the original biota becomes increasinglyun- likely,due to lower probabilitiesof dispersal from undisturbedsites.The high incidenceof geographic endemics suggeststhat numerousspecies may face extinction. The destructionof caatinga vegetationin areas of Amazonia designatedfordevelopmentraises the question of whetherthese habitats will recuperate in time,and how muchtimewill be required.While thereare no definitiveanswers,clues may be found by examining the origin and successionalstatusof non-forestvegetationon whitesand. 206 Anderson
  10. 10. ORIGIN AND SUCCESSION The incidenceof non-forestvegetationin the Ama- zon region is surprisinglyhigh. Pires (1974) esti- mated that over 226,000 square kilometersof Bra- zilian Amazonia are covered by savanna or scrub. The origin of such vegetation is uncertaindespite much speculationin the literature(cf. Hills 1969, Sarmientoand Monasterio 1975). Althoughwhite- sand savanna and scrubare probablyproducedby a varietyof factors,two appear to be of overriding significance:positionand stabilityof thewatertable, and fire. White-sand soils can be characterizedas either hydromorphicor non-hydromorphic,depending on whetherthe water table remainswithin a meterof thesurfaceovermostof theyear.Hydromorphicand non-hydromorphicsoils supportdistinctfloristicas- sociations,even where they occur adjacent to one another (Heyligers 1963, Anderson 1978). On hy- dromorphicso,ils,the positionof the watertable ap- pears to be a crucial factorin determiningvegeta- tion structure.In his exhaustivestudyof white-sand vegetationin Surinam,Heyligers (1963) foundthat savanna is situatedin areas where the water table remainsconstantlyat the surface,while less-reduced scrub occurs on slightlymore-elevatedsites, where thewatertable is deeperand rootsystemsapparently attain greater development.Stabilityof the water tablemayalso determinevegetationstructurein these habitats.In white-sandsavanna and scrub ("bana") in Venezuela, Herrera (1977) foundthatthe water table drops fromthe surfaceto over 100 cm depth duringperiodsof low rainfall;simultaneousmeasure- ments under white-sand forest ("yaguacanan") showed negligible variation. A fluctuatingwater table may exerta detrimentaleffecton the vegeta- tion through decreased water availability and/or increasedleachingwithinthe rootzone. In contrast,Heyligers(1963) foundthaton non- hydromorphicsites,vegetationstructurebears little relationto po,sitionof water table or its degree of fluctuation.A more potent factor in determining vegetationstructureon thesesites is fire.In central Amazonia, the presence of charcoal and ceramic shards at a number of reduced caatinga sites led Prance and Schubart (1977) to conclude that the presentstructureof the vegetationis due to fire.In Malaysia,white-sandsavanna and scrub ("padang") are producedby fire (Whitmore 1975), and similar habitats in Surinam are still frequentlyburned by Indiansduringthedryseason (Heyligers 1963, Stark 1970). Nor is vegetationon hydromorphicsandsim- mune: Indians in Surinam occasionally burn such sites to facilitate capture of tortoises (Heyligers 1963). In northernSouth America, white-sandforests or woodlands destroyedby fireare initiallyrecolon- ized by typicalsecondaryelementssuch as Cecropia, Vismia,Byrsonima,and Pteridium(Ducke and Black 1953, Heyligers1963). Althoughinitialcolonization is rapid, subsequent growth is considerablyslower than on oxisols. Ten years after.a burn, Heyligers (1963) observedthatmost of the initial colonizers had died, and thatscatteredwhite-sandspecies such as Dirnorphandraconjugata were graduallybecom- ing reestablished.On a siteburned30 yearsprevious- ly, he found a scrub dominatedby Dirnorphandra; 50 years aftera burn, a white-sandwoodland had developed. In the continued absence of fire,Hey- ligersconcludedthatforestwould eventuallydevelop on these sites. Although regenerationdoes occur when white- sandvegetationis subjectedto fire,successionappears to be comparativelyprolonged,as indicated by the slowgrowthof secondarycolonizersfollowinga burn. Successionmaybe even more prolongedif a burn is widespread. As was mentioned above, fires which destroywhite-sandvegetationover largeareas reduce the probabilityof dispersal fromundisturbedsites and thus may prolong succession. Intensityof the burnis an additionalfactor.Heyligers(1963) found that followinga light to moderateburn,a number of fire-resistantspecies such as Dimorphandraserve as "regenerationcenters,"providinga focalpoint for establishmentof colonizing species; intensiveburns destroythesecentersand thusappear to,prolongsuc- cession. Repeated burnshave a similareffect.Based on observationsin Brazil and Surinam,Stark (1970) suggestedthatfouror fiveburnsof whatwas initially white-sandforestproduce sites which are devoid of vegetationand severelydepleted in nutrients.The long-termeffectsofwhatwereapparentlywidespread, intensive,or repeatedburnscan be seen today.Radio- carbon dating of charcoal remains found on bare- sand sites in central Amazonia indicates that the vegetationwas burned 800-1100 yearsago (Prance and Schubart 1977). Lack of regenerationduring thistime impliesthatsuccessionhas been effectively arrestedon thesesites. The above considerationsindicate that white- sand vegetation has a low resilience to externally imposed stressessuch as fire.Above-groundbiomass and litterstorean exceptionallylarge proportionof total nutrientsin these ecosystems(Herrera et al. 1978). Burningof the vegetationis likelyto cause considerablelosses of released nutrients,due to the low storagecapacityofthesoil.On non-hydromorphic White-Sand Vegetation of Amazonia 207
  11. 11. sites,thethicksurfacerootmatis relativelysuscepti- bletodestructionbyfire(fig.9), leadingto further nutrientlosses.Failureof rapidreestablishmentfol- lowingwidespread,intensive,or repeatedburnsmay thusresultin a depletionof soil nutrientsbelow levelsnecessaryforplantgrowth.Attemptsto re- establishproductiveforestson suchsitesare likely to fail,as indicatedby trialplantingon degraded white-sandsoilsin Malaysia(Mitchell1963). With- outa viablenutrientstoragecomponent,successionis effectivelyarrestedand a biologicaldesertis pro- duced. THE VALUE OF THE AMAZON CAATINGA A lowresiliencetoexternalstresses,inadditiontoun- favorablesoil conditions,indicatesthattheAmazon caatingahas littlepotentialforagriculture.Indeed, similarvegetationin Malaysiais referredto as "ker- angas,"meaning"forestwhich,when cleared,will notgrowrice" (Whitmore1975:132). At present, theirlackofagriculturalvalueappearsto justifythe use of caatingasitesas a sourceof sand forroad- buildingand constructionprojectsthroughoutAma- zonia (fig.10). The valueofthecaatingain itsin- tactstatehas notbeen consideredwhencalculating thecostof extractingitssand. An accurateknowledgeof the extentand dis- tributionof thesehabitatsin Amazoniais a pre- requisitefordeterminingviablealternativesforland use.The Amazoncaatingahasneverbeenaccurately mapped,althoughsatelliteimagesnow providethe meansto do so. The highreflectanceof thevegeta- tionand soil,as well as therelativeuniformityof the canopy,producesa distinctivelypale toneand finetextureonaerialphotographs(Whitmore1975), makingthesehabitatsamenableto mapping.Sucha map wouldbe usefulfortworeasons.First,by in- dicatingsitesof highendemism,it wouldprovidea criterionforthe locationand delimitationof bio- logicalreservesin Amazonia.Second,by indicating sitesof low agriculturalpotential,it wouldprovide a criterionforthelocationanddelimitationof focal pointsfordevelopmentwithintheregion.This last criterioncouldhave been usefullyappliedpriorto theestablishmentof an extensiveagriculturalzone on theManaus-BoaVistahighway(BR-174 km35- 105): a highincidenceofcaatingavegetationfaith- fullyatteststotheoverallimpoverishedstateofsoils in thiszone. The value of white-sandhabitatsultimatelyde- pendson whatalternativebenefitstheycan provide. CarefullymanagedforestshomologoustotheAmazon 9 _ :7~~~~~~~~~~~~~~.~~~~~~. .. ..... 10 FIGURES 9-10. Figure 9. Burned caatinga, with surface root mat and litterreducedto ash (BR-174 km ca. 25). Figure 10. Caatingasiteminedforsand,withcementfactory in background(AM-070 km ca. 75). caatingaareusedas a continuingsourceoftimberin Malaysia(Whitmore1975). The recreationalvalue of white-sandvegetationwithintheBako National ParkinSarawakis increasinglyappreciatedbyurban visitors(Whitmore1975). The relativesimplicity of the caatingamakesit ideal foreducationaland researchpurposes,as indicatedbythe intensiveuse of one such site in centralAmazonia (Reserva Biol6gicado INPA/SUFRAMAI,BR-174 km 45). Finally,theunusualfloraandfaunain thesehabitats areofvaluenotonlyforaestheticreasons.Withthe implementationofman-madeecosystemsthroughout thehumidtropics,organismsadaptedto high-stress environmentssuchas theAmazoncaatingaarelikely to becomeincreasinglyimportantas a geneticre- source. ACKNOWLEDGEMENTS Many of the ideas presentedin this paper have come from discussionswith W. W. Benson, P. I. S. Braga, L. Coelho, S. B. Hecht, C. F. Jordan,P. L. Lisb6a, E. P. Lleras, E. Medina, D. C. Oren, J. M. Pires, H. L. Popenoe, G. T. Prance,G. Ranzani, J. Revilla, W. A. Rodrigues,H. 0. R. 208 Anderson
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