Abstract

The Serra do Divisor National Park (SDNP) in the Westernmost Brazilian Amazonia possesses unique Mountain landscapes of sub-andean nature, with high geo-biodiversity and pristine environments, with a potential high contribution in ecosystems services. We studied and mapped the basic geo-environmental units of the main sector of the Park, evaluating soil carbon stocks as a key ecosystem service provided by the Protected Area. For the identification, characterization and mapping of the geoenvironmental units, we integrated pedological, geomorphological and vegetation data obtained by local soil survey and field campaigns, as well as secondary data. Eight geoenvironmental units were identified and mapped, distributed in three main compartments: the Serra do Divisor (SD) the upper Moa River and the medium Moa River. This region presents similar environments to the sub-Andean region, notably the Ceja Forest at the top surface of the SD. Soils at the SD have high organic carbon accumulation, with close association with the nutrient-poor, quartz-rich rocks, and shows organic matter illuviation indicating active podzolization. The SDNP encompasses important ecosystems and services linked with high geo-biodiversity, and high soil carbon stocks, representing a new frontier for scientific research in the only area of transitional sub-andean forested landscape in Brazil.

Key words
Carbon stocks; geodiversity; mountain soils; pedogeomorphology

INTRODUCTION

Located in the upper Juruá River region, in the westernmost part of the State of Acre (Western Amazon, Brazil), the Serra do Divisor National Park (SDNP) encompass 784,077 hectares covered by different types of primary forest, presenting one of the highest biodiversity in the Amazon (Silveira & Daly 1997SILVEIRA M & DALY D. 1997. Florística e Botânica Econômica do Acre. Relatório Final (1993-1997). UFAC/The New York Botanical Garden/CNPq/NSF, Rio Branco.). The presence of a prominent mountain range, called Serra do Divisor, is a striking feature of the Park, representing an exceptional landscape to the surrounding forested lowlands of the upper Juruá (Schaefer et al. 2023SCHAEFER CEGR, LIMA HN, TEIXEIRA WG, VALE JUNIOR JF, CORRÊA GR, MENDONÇA BAF, MELO VF, AMARAL EF, CAMPOS MCC & RUIVO MLP. 2023. Soils from Brazilian Amazonia. In: SCHAEFER CEGR (Org). The Soils of Brazil. 1 ed. Springer, 85-128 p. https://doi.org/10.1007/978-3-031-19949-3_4.
https://doi.org/10.1007/978-3-031-19949-... ). Since the pioneer studies of von Humboldt in the early nineteenth century, altitudinal zoning is considered a key aspect accounting for variation in vegetation and biodiversity in Amazonian ecosystems (Ab’Saber 2002AB’SABER AN. 2002. Bases para o estudo dos ecossistemas da Amazônia brasileira. Revista Estud Av 16(45): 7-30. https://doi.org/10.1590/S0103-40142002000200002.
https://doi.org/10.1590/S0103-4014200200... ).

The SDNP creation was supported by studies carried out in the late seventies (Brown Jr 1977BROWN JR KS. 1977. Centros de evolução, refúgios quaternários e conservação de patrimônios genéticos na região neotropical: padrões de diferenciação em Ithomiinae (Lepidoptera – Nymphalidae). Acta Amazônica 7: 75-137., Haffer 1969HAFFER J. 1969. Speciation in Amazonian forest birds. Science 165: 131-137., 1974HAFFER J. 1974. Avian speciation in tropical South America. Nuttall Ornith. Club No. 14, Cambridge, Mass., 1992HAFFER J. 1992. Ciclos de tempo e indicadores de tempos na história da Amazônia. Rev Estud Av 6(15)., Pires 1974PIRES JM. 1974. Tipos de vegetação da Amazônia. Bras Florest 5(17): 48-58., Pires & Prance 1985PIRES JM & PRANCE GT. 1985. The Vegetation Types of Amazon. In: PRANCE GT & LOVEJOY TE (Eds). Key Environments: Amazonia. Ed. Pergamon Press, England, 83-94 p., Prance 1979PRANCE GT. 1979. Phytogeographic support for the theory of Pleistocene forest refuges in the Amazon Basin, based on evidence from distribution patterns in Caryocaraceae, Chrysobalanaceae, Dichapetalaceae and Lecythidaceaea. Acta Amazônica 3(1): 5-28., Wetterberg et al. 1976WETTERBERG GB ET AL. 1976. Uma análise de prioridades em conservação da natureza na Amazonia. Projeto de Desenvolvimento e Pesquisa Florestal (PRODEPEF) PNUD/FAO/IBDF/BRA- 45. Série Técnica 8, 63 p.), which identified priority areas for the creation of Protected Areas (PAs) in the Amazon, located in centers of high endemism for different groups of species. These regions would represent Late Quaternary forest refuges, resulting from the contraction of the rainforest during colder and drier climatic periods (Whitemore & Prance 1987WHITEMORE TC & PRANCE GT (Eds). 1987. Biogeography and Quaternary History in Tropical America. Clarendon Press, Oxford.), and possessing high biodiversity. These facts highlight the importance of building up more detailed informations on little known areas to support the Amazonian conservation plans (Lovejoy 1985LOVEJOY TE. 1985. Amazonia, people and today. In: PRANCE GT & LOVEJOY TE (Eds). Key Environments: Amazonia. Ed. Pergamon Press, England, 328-338.), since large extensions are necessary for the preservation of endangered ecosystems (Laurence et al. 2002LAURENCE WF, LOVEJOY TE, VASCONCELOS HL, BRUNA EM, DIDHAM RK, STOUFFER PC, GASCON C, BIERREGAARD RO, LAURENCE SG & SAMPAIO E. 2002. Ecossystem Decay of Amazonian Forest Fragments: a 22-Year Investigation. Conserv Biol 16(3): 605-618., Lovejoy 1985LOVEJOY TE. 1985. Amazonia, people and today. In: PRANCE GT & LOVEJOY TE (Eds). Key Environments: Amazonia. Ed. Pergamon Press, England, 328-338., Peres 2005PERES CA. 2005. Porque precisamos de megareservas na Amazônia. Revista Megadiversidade 1(1).).

The great isolation of the SDNP severely constrains environmental studies at adequate scales for conservation planning and monitoring. In particular, pedological studies are extremely important in management plans, since they are good stratifiers of natural landscape units (Santana 1983SANTANA DP. 1983. A importância da classificação de solos e do meio ambiente na transferência de tecnologia. Inf Agropecu 9(105): 79-82., Resende & Rezende 1983RESENDE M & REZENDE SB. 1983. Levantamento de solos: uma estratificação de ambientes. Inf Agropecu 9(105): 3-25., Resende et al. 1995RESENDE M, CURI N, REZENDE SB & CORRÊA GF. 1995. Pedologia: bases para a distinção de ambientes. NEPUT, Viçosa., Dias et al. 2001DIAS HCT, FERNANDES-FILHO EI, SCHAEFER CEGR, FONTES LEF & VENTORIM LB. 2001. Geoambientes do Parque Estadual do Ibitipoca, município de Lima Duarte, MG. Revista Árvore 26: 777-786. https://doi.org/10.1590/S0100-67622002000600014.
https://doi.org/10.1590/S0100-6762200200... , Brandão et al. 2010BRANDÃO PC, SOARES VP, SIMAS FNB, SCHAEFER CEGR, SOUZA AL & MENDONÇA BAF. 2010. Caracterização de Geoambientes da Floresta Nacional do Purus, Amazônia Ocidental: uma contribuição ao Plano de Manejo. Revista Árvore 34(1): 115-126. https://doi.org/10.1590/S0100-67622010000100013.
https://doi.org/10.1590/S0100-6762201000... , Mendonça et al. 2013MENDONÇA BAF, FERNANDES-FILHO EI, SCHAEFER CEGR, SIMAS FNB, VALE JÚNIOR JF, LISBOA BAR & MENDONÇA JGF. 2013. Solos e Geoambientes do Parque Nacional do Viruá e entorno, Roraima: visão integrada da paisagem e serviço ambiental. Rev Cienc Florest 23(2): 427-442. https://doi.org/10.5902/198050989287.
https://doi.org/10.5902/198050989287... ). Hence, integrated pedological, geomorphological, geological and vegetation studies allows the identification of geoenvironmental units, having unique ecogeographic features and geoenvironmental problems. These units constitute an integrated framework very efficient for the management and monitoring of natural resources in Amazonia (Schaefer et al. 2000SCHAEFER CEGR, ALBUQUERQUE MA, CHARMELLO LL, CAMPOS JCF & SIMAS FNB. 2000. Elementos da Paisagem e a Gestão da Qualidade Ambiental. Info Agropecu 21., 2020SCHAEFER CEGR, CAMPOS PV, CANDIDO HG, CORRÊA GR, FARIA RM & VALE JÚNIOR JF. 2020. Serras e pantanais arenosos: solos e geoambientes em unidade de conservação da Amazônia, Brasil. Neotrop Biol Conserv 15(1): 43-69., Brandão et al. 2010BRANDÃO PC, SOARES VP, SIMAS FNB, SCHAEFER CEGR, SOUZA AL & MENDONÇA BAF. 2010. Caracterização de Geoambientes da Floresta Nacional do Purus, Amazônia Ocidental: uma contribuição ao Plano de Manejo. Revista Árvore 34(1): 115-126. https://doi.org/10.1590/S0100-67622010000100013.
https://doi.org/10.1590/S0100-6762201000... , Mendonça et al. 2013MENDONÇA BAF, FERNANDES-FILHO EI, SCHAEFER CEGR, SIMAS FNB, VALE JÚNIOR JF, LISBOA BAR & MENDONÇA JGF. 2013. Solos e Geoambientes do Parque Nacional do Viruá e entorno, Roraima: visão integrada da paisagem e serviço ambiental. Rev Cienc Florest 23(2): 427-442. https://doi.org/10.5902/198050989287.
https://doi.org/10.5902/198050989287... ).

In addition, geoenvironmental units can be used for evaluating ecosystem services, especially for quantifying the soil/biomass carbon stocks (Mendonça et al. 2013MENDONÇA BAF, FERNANDES-FILHO EI, SCHAEFER CEGR, SIMAS FNB, VALE JÚNIOR JF, LISBOA BAR & MENDONÇA JGF. 2013. Solos e Geoambientes do Parque Nacional do Viruá e entorno, Roraima: visão integrada da paisagem e serviço ambiental. Rev Cienc Florest 23(2): 427-442. https://doi.org/10.5902/198050989287.
https://doi.org/10.5902/198050989287... ), and potential losses upon conversion to other uses (Fearnside 2018FEARNSIDE PM. 2018. Brazil’s Amazonian forest carbon: the key to Southern Amazonia’s significance for global climate. Reg Environ Change 18: 47-61. doi:10.1007/s10113-016-1007-2.). Fearnside (1997FEARNSIDE PM. 1997. Environmental services as a strategy for sustainable development in rural Amazonia. Ecol Econ 20(1): 1-70. doi:10.1016/s0921-8009(96)00066-3., 2003) proposed that the Amazon ecosystem services are basically: (i) biodiversity maintenance, (ii) carbon storage and (iii) water cycling, representing the benefits that the society obtain from natural ecosystems. It is unclear that Amazon nations will benefit from these ecosystem services in the coming future (Phillips et al. 2017PHILLIPS OL, BRIENEN RJW & THE RAINFOR COLLABORATION. 2017. Carbon uptake by mature Amazon forests has mitigated Amazon nations’ carbon emissions. Carbon Balance Manage 12(1). https://doi.org/10.1186/s13021-016-0069-2.
https://doi.org/10.1186/s13021-016-0069-... ), although it is recognised that mature forests contributes with substantial net sequestration of carbon, helping in global climate change mitigation.

Thus conservation of soil carbon stocks is one of the many ecosystem services offered by the Amazon region (Fearnside 2003FEARNSIDE PM. 2003. A floresta amazônica nas mudanças globais. INPA, Manaus, 134 p., Adhikari & Hartemink 2016ADHIKARI K & HARTEMINK AE. 2016. Linking soils to ecosystem services — A global review. Geoderma 262: 101-111. https://doi.org/10.1016/j.geoderma.2015.08.009.
https://doi.org/10.1016/j.geoderma.2015.... ). Interest in carbon cycling, both emissions or sinks have increased since the adoption of Kyoto Protocol (UN-FCCC 1997UN-FCCC. 1997. Kyoto Protocol to the United Nations Framework Convention on Climate Change. United Nations Framework Convention on Climate Change Document FCCC/CP.). More recently, Stern & Stiglitz (2017)STERN N & STIGLITZ JE. 2017. Report of the high-level commission on carbon prices. World Bank, Washington. postulated that supportive policies would have a carbon-price level at the range of US$40–80/tCO₂, but little has been made to estimate and evaluate the contributions of Protected Areas in the global carbon stocks.

Hence, we aimed to identifying, characterizing and mapping of soils and geoenvironments of the main sector of the SDNP, using a geoenvironmental approach. From the integration of the data, the soil carbon stock were estimated for soils mapping units and geoenvironments, allowing key aspects of the ecosystem services to be discussed.

MATERIALS AND METHODS

Study area

Located in the northwest of the state of Acre (Figure 1), along the Brazil-Peru border, the SDNP comprises part of the important set of mountains known as Serra de Contamana, or Serra do Divisor on the Brazilian side, the eastern end of the Andean Eastern Range (Moura & Wanderley 1938MOURA P & WANDERLEY A. 1938. Noroeste do Acre: reconhecimentos geológicos para petróleo. DNPM, Rio de Janeiro., Brasil 1977BRASIL. 1977. Folhas SB/SC. 18 Javari/Contamana; geologia, geomorfologia, pedologia, vegetação e uso potencial da terra. Ministério das Minas e Energia, Rio de Janeiro.). In the present work the northern sector of the SDNP and its surroundings in the Brazilian territory with a 10 km buffer was studied (Figure 1). This region constitutes an important watershed between the Juruá and the Mid Ucayali River (Peru). In the Serra do Divisor the altitudes reaches 700 m, with 200 m average in the surrounding region.

The climate is Af (Köppen), without a defined dry season, with a mean annual rainfall of 2,333 mm, and the mean annual temperature 23.0 °C; July is the coldest month with mean temperatures of 20.7 °C, and the warmest month is March with 25.0 °C (Alvares et al. 2013ALVARES CA, STAPE JL, SENTELHAS PC, GONÇALVES JLM & SPAROVEK G. 2013. Köppen’s climate classification map for Brazil. Meteorol Z 22: 711-728. https://doi.org/10.1127/0941-2948/2013/0507.
https://doi.org/10.1127/0941-2948/2013/0... ).

The Serra do Divisor represents the easternmost anticlinal folds of the Eastern Andes Cordillera, belonging to the same tectonic cycle. It is composed by very distinct lithostratigraphic units of Paleozoic age (Formosa Formation and Syenite República) and Mesozoic (Ramon Formation - Tr, Moa Formations - Km, Rio Azul Formation - Kra, Divisor Formation - Kd); in the surrounding lowlands, Cenozoic sediments of the Solimões Formation (TQs), and Quaternary Alluvial (Qai) and Colluvial (Qc) Formations widely occur (Brasil 1977BRASIL. 1977. Folhas SB/SC. 18 Javari/Contamana; geologia, geomorfologia, pedologia, vegetação e uso potencial da terra. Ministério das Minas e Energia, Rio de Janeiro.).

The major vegetation types of SDNP are Open Alluvial Ombrophilous Forest with Palms and with Bamboo, Lowland Dense Ombrophilous Forest, and Submontane Dense Ombrophilous Forest (IBGE 2005IBGE. 2005. Vegetação. Estado do Acre. Escala 1:1.000.000. Coordenação de Recursos Naturais e Estudos Ambientais. Diretoria de Geociências. Instituto Brasileiro de Geografia e Estatística.). The Submontane Dense Forest occurs only in this part of Acre state (Silveira et al. 2008SILVEIRA M, DALY DC, SALIMON CI, WADT PGS, AMARAL EF, PEREIRA MG & PASSOS V. 2008. Ambientes físicos e coberturas vegetais do Acre. Primeiro Catálogo da flora do Acre, Brasil. Rio Branco, AC: EDUFAC 1: 36-63.). Some small areas with degraded grasslands with livestock is also found in the SDNP vicinities (IBGE 2005IBGE. 2005. Vegetação. Estado do Acre. Escala 1:1.000.000. Coordenação de Recursos Naturais e Estudos Ambientais. Diretoria de Geociências. Instituto Brasileiro de Geografia e Estatística.).

Soil physical and chemical analysis

Eight representative soil profiles (P1 to P8) were selected, described, collected, analyzed and classified. They are located at the northern sector of the SDPN in the two main landscapes, representing different geomorphic settings and vegetation types: P1 to P4 form a topossequence in the Serra do Divisor landscape, whereas P5 to P8 are soils along the Moa river valley. These soils were also studied by Mendonça et al. (2020)MENDONÇA BAF, FERNANDES-FILHO EI, SCHAEFER CEGR, SIMAS FNB & AMARAL EF. 2020. Genesis and micropedology of soils at Serra do Divisor and Moa river floodplain, northwestern Acre, Brazilian Amazonia. Rev Bra Cienc Solo 44: e0200038. https://doi.org/10.36783/18069657rbcs20200019.
https://doi.org/10.36783/18069657rbcs202... , with emphasis on soil genesis and micropedological aspects. Figure 1 illustrates the location of the profiles collected, representing different parent materials. All profiles were collected and described according to Santos et al. (2005)SANTOS RD, LEMOS RC, SANTOS HGDOS, KER JC & ANJOS LHC. 2005. Manual de descrição e coleta de solo no campo. Sociedade Brasileira de Ciência de Solo, Viçosa., and classified according to the USDA Soil Taxonomy System (Soil Survey Staff 2014SOIL SURVEY STAFF. 2014. Keys to Soil Taxonomy. United States Department of Agriculture, Washington.).

The samples were air-dried and passed through a 2-mm sieve, obtaining the air-died fine earth, which was submitted to the following physical and chemical analyzes: particle size determined by the dispersion with 0.1 mol L^-1 NaOH and stirring, sieving for the sand fractions, the clay fraction determined by the pipette method, and the silt fraction calculated by difference (Ruiz 2005RUIZ HA. 2005. Incremento da exatidão da análise granulométrica do solo por meio da coleta da suspensão (silte + argila). Rev Bra Cienc Solo 29: 297-300. https://doi.org/10.1590/S0100-06832005000200015.
https://doi.org/10.1590/S0100-0683200500... ); pH in water and KCl 1 mol L^-1, determined potentiometrically soil/solution (1:2.5); exchangeable calcium, magnesium and aluminum concentrations extracted with KCl 1 mol L^-1 in the ratio 1:20 and determined by atomic absorption spectrometry; exchangeable potassium and sodium extracted with Mehlich-1 solution and determined by flame photometry; (Mehlich-1) and determined by colorimetry in the presence of ascorbic acid (Defelipo & Ribeiro 1997DEFELIPO BV & RIBEIRO AC. 1997. Análise Química do Solo. UFV, Viçosa, 26 p.); the potential acidity was determined by titration with NaOH (0.025 mol L^-1) from the extraction of 0.5 mol L^-1 calcium acetate at pH 7.0; and Total Organic Carbon (TOC) was determined using the method of Yeomans & Bremner (1988)YEOMANS JC & BREMNER JM. 1988. A rapid and precise method for routine determination of organic carbon in soil. Commun Soil Sci Plant Anal 19(13): 1467-1476. https://doi.org/10.1080/00103628809368027.
https://doi.org/10.1080/0010362880936802... .

Geoenvironments units and stratification

For the identification and stratification of the geoenvironmental units a pedo-geomorphological approach was used, identifying the ecogeographic characteristics and associated geoenvironmental problems (Tricart & Kiewitdejonge 1992TRICART J & KIEWITDEJONGE C. 1992. Ecogeography and rural management. Harlowl: Longman Scintific., Schaefer 1997SCHAEFER CEGR. 1997. Ecogeography and Human Scenario. In: Roraima, Amazonia. Ciência e Cultura 49(4): 241-252., Brandão et al. 2010BRANDÃO PC, SOARES VP, SIMAS FNB, SCHAEFER CEGR, SOUZA AL & MENDONÇA BAF. 2010. Caracterização de Geoambientes da Floresta Nacional do Purus, Amazônia Ocidental: uma contribuição ao Plano de Manejo. Revista Árvore 34(1): 115-126. https://doi.org/10.1590/S0100-67622010000100013.
https://doi.org/10.1590/S0100-6762201000... ). The geoenvironmental mapping units have distinct physiographic units, based on pedological, geomorphological, geological and vegetation characteristics. All secondary data was obtained from the Ecological-Economic Zoning of Acre (Acre 2006ACRE. 2006. Governo do Estado do Acre. Programa Estadual de Zoneamento Ecológico-Econômico do Acre. Zoneamento Ecológico-Econômico do Acre Fase II: documento síntese. SEMA, Rio Branco.), at a scale of 1: 250.000, which was integrated for identifying and mapping the geoenvironmental units.

Each pedological, geomorphological, geological, and vegetation shapefiles were transformed into a raster with a number identification for each class. The soil classes were multiplied by 10, the geological classes by 100, the geomorphological classes by 1000, and we sum all units including vegetation classes. The results represent many units with 4 digit, each one indicating specific geoenvironmental units. We also eliminated all units below 1000 ha, due to scale limitation. We combined these results with aerial photographs (1:10,000) in a transect ranging from the Serra do Divisor to the Moa River floodplain (Rezende 2006REZENDE SB. 2006. Levantamento aerofotogramétrico na Serra do Divisor. NEPUT, Viçosa.), images from the Landsat 5 TM satellite, obtained on September 23, 2005; and images of the Shuttle Radar Topographic Mission – SRTM for adjusting and refining the final mapping of the geoenvironmental units. We also used the soil data collecting and data from the RADAMBRASIL Project (Brasil 1977BRASIL. 1977. Folhas SB/SC. 18 Javari/Contamana; geologia, geomorfologia, pedologia, vegetação e uso potencial da terra. Ministério das Minas e Energia, Rio de Janeiro.). All data were processed using ArcGIS 10.0 software.

Soil carbon stocks and value estimatives

For estimating the soil carbon stock we used the 8 soil profiles studied in addition to 17 reference profiles previously studied by the RADAMBRASIL project (Brasil 1977BRASIL. 1977. Folhas SB/SC. 18 Javari/Contamana; geologia, geomorfologia, pedologia, vegetação e uso potencial da terra. Ministério das Minas e Energia, Rio de Janeiro.), so that all soil units were represented. The soil carbon stock was estimated for each geoenvironmental unit, considering the relative proportion of each soil class. The relative stock of C by soil class ECp (kg m^-2) was calculated from the weighted average of all genetic horizons (A, B and C), multiplying the concentration of C (%), soil density (SD) (kg m^-3) and thickness h (meters) of each horizon. The litter was not included in the calculation according due to high variability. The calculation was the sum of C stocks at each horizon, so the total soil carbon stock refers to the depth of the deepest horizons at each soil. SD was estimated using an equation that relate clay content (CC) and organic carbon (OC) with SD, obtained from Bernoux (1998)BERNOUX M. 1998. Conteúdo de carbono dos solos da Amazônia ocidental e mudanças decorrentes da conversão da floresta em pastagens. Doctoral thesis, Universidade de São Paulo. and Bernoux et al. (1998BERNOUX M, ARROUAYS D, CERRI C, VOLKOFF B & JOLIVET C. 1998. Bulk densities of Brazilian Amazon soils related to other soil properties. Soil Sci Soc Am J 62(3): 743-749. https://doi.org/10.2136/sssaj1998.03615995006200030029x.
https://doi.org/10.2136/sssaj1998.036159... , 2002BERNOUX M, CARVALHO MCS, VOLKOFF B & CERRI C. 2002. Brazil’s Soil Carbon Stocks. Soil Sci Soc Am J 66: 888-896. https://doi.org/10.2136/sssaj2002.8880.
https://doi.org/10.2136/sssaj2002.8880... ). For soils with clay content ≤ 20%, the following equation was used: SD = 0.0181 x (100 - CC - 5) - 0.08 x OC, r² = 0.66.

For soils with more than 20% clay, the SD calculation was made according to Houghton et al. (1997)HOUGHTON JT, MEIRA FILHO LG, LIM B, TREANTON K, MAMATY I, BONDUKI Y, GRIGGS DJ & CALLENDER BA. 1997. Revised 1996 IPCC guidelines for national greenhouse gas inventories: Reference manual. IPCC/OECD/IEA, London., for grouping soil densities values for inventories. The groups of soils were: G1 – Haplic Cambisols, Luvisols, Litholic Neosols and Argisols – SD = 1.394 - (0.0051 x CC) - (0.037 x OC), r² = 0.47; G2 – Fluvic Cambisols and Neosols, Gleysols, Vertisols and Plinthosols – SD = 1.369 - (0.0042 x CC) - 0.04 x OC, r² = 0.46; and G3 – Latosols – SD = 1.404 - (0.0040 x CC) - (0.048 x OC), r² = 0.71. Where: SD = soil bulk density by weight (g cm^-3); CC = clay content, after dispersion with NaOH 0.1 mol L- (% [weight / weight] of soil fraction <2 mm); OC = organic carbon [% (w/w) of the soil fraction <2 mm] (Yeomans & Bremner 1988YEOMANS JC & BREMNER JM. 1988. A rapid and precise method for routine determination of organic carbon in soil. Commun Soil Sci Plant Anal 19(13): 1467-1476. https://doi.org/10.1080/00103628809368027.
https://doi.org/10.1080/0010362880936802... ).

For valuating the carbon stocks we considered a mean value (US$60/tCO₂) of the Stern & Stiglitz (2017)STERN N & STIGLITZ JE. 2017. Report of the high-level commission on carbon prices. World Bank, Washington. study. This estimae is based on the literature on carbon prices for the Paris agreement, at a range of US$40–80/tCO₂ by 2020 (Stern & Stiglitz 2017STERN N & STIGLITZ JE. 2017. Report of the high-level commission on carbon prices. World Bank, Washington.); the convertion of C soil stocks to CO₂ used the 1 GtC = 3.7 GtCO₂ (IPCC 2007IPCC. 2007. Climate Change 2007: Synthesis Report. Contribution of Working Groups I, II and III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. IPCC, Geneva, Switzerland, 104 p.).

RESULTS

Soils of the Serra do Divisor

The typical topossequence of soils at the Serra do Divisor (P1 to P4) developed on the Moa Formation (Cretaceous Sandstones), has steep slopes and mountainous relief, with ridges and deeply dissected landforms, which favors mass movement, corroborated by the many landslides scars along the slopes. Topographic variations of the sandy parent material are drivers of soil formation and vegetation establishment. All four soils along the topossequence have unusual surface horizons with high amounts of fibric organic matter with little decomposition rate, from dark to very dark colors (Table I), indicating environmental conditions favorable to carbon accumulation in histic or humic horizons. In this soil topossequence, highland soils (P1 and P2) have more stable landform and thicker histic horizons. The sandy nature of the parent material results in weel-drained soils, with high porosity and permeability of the weathered quartz-rich sandstone, at the high mountain surface and slopes.

The mineral horizons have very low fertility and high acidity due to the chemical infertility of the sandy parent material (Cretaceous Sandstone), with bases sum nearly zero (Table I). In soils P1 and P2 the accumulation of 40 cm thick fibrous organic matter has very dark colors, associated with the partially decomposed remains of dacaying bromeliads that dominate the herbaceous cover (Figure 2).

All soils are sandy to loamy-sand (Table I). They all have low effective CEC, marked dystrophy, high Al⁺³ contents in the exchange complex and high TOC contents, especially in the surface horizons (Table I). The low pH increasing with depth, show the acidic nature of the organic matter (Table I). Besides CEC, base saturation and exchangeable Al contents decrease in depth, accompanying the decreasing organic carbon content. This indicates the importance of soil organic matter in nutrient cycling and fertility in these acid soils (Table I). Surface horizons present higher nutrient content, with higher contents of P, K, Na, Mg, Zn and Mn, directly associated with organic matter and nutrient cycling (Table I), corroborating the very poor chemical status of the regional sandstone parent materials.

Soils of the Moa River floodplain

In general, soils of the Moa river floodplain have higher values of Bases sum and CEC than soils on Serra do Divisor, due to the greater clay contents, higher electric charges and nutriente contentes. Under hotter climates, the with higher mineralization rates makes the soil organic carbon contents much lower than the acid soils of Serra do Divisor (Table I).

At the transitional zone, P5 is located near the foothills of Serra do Divisor, and presents high amounts of fine sand on Alluvial sediments, from the dismantling and erosion of Cretaceous Sandstones, upslope. The observed lithological discontinuities evidenced by color and textural changes, corroborates a polycyclic natural of footslopes soils. P6, P7 and P8 present a textural gradient, of abrupt nature in the last two soils. The P6 is developed on mudstones of Solimões Formation, and the ferrolysis process of clay destruction was identified in the AE horizon (Table I). In terms of soil fertility, P6 is the most nutrient deficient, and used by extensive cattle grazing. The available P contens, and values of SB, V and TOC gradually decrease in depth, and most nutrients are associated with organic matter and at the soil surface (Table I).

P7 has a eutrophic character, possibly due to the presence of minute CaSO₄/CaCO₃ concretions, commonly observed in the Solimões Formation. Plinthite has been identified in the Bt1 horizon of P8, and indicates the occurrence of seasonal variations of redox potential in the terraces of the Moa River, leading to mottling and segregation of Fe nodules and plinthites ill drainage. These soils are mostly used for pasture and grazing.

Geoenvironments and soil carbon stocks

Eight geoenvironmental units were identified and described in the SDNP (Figure 3 and Table II). In general, the landscape was stratified into three large environmental compartments, associated with geological, pedological and geomorphological characteristics: (1) the first one, the Serra do Divisor is composed of nutrient poor, dystrophic soils with sandy texture, with significant accumulation of organic material on the surface above 400 meters. The low total C stocks (5,866.14 Gg C) is due to its small extension, but these soils have the largest C stocks/unit area; (2) the Upper Rio Moa, with predominant eutrophic soils with carbonates, and some vertic character, represent a landscape with young, high fertility soils, representing 11,508.61 Gg C of total soil carbon stocks; and (3) the Middle Moa River has poorly developed soils with shallow A horizon, high exchangeable Al contents, and natural fertility closely associated with nutrient cycling at the surface, usually with high watertable. Due to its vast extension, it the largest carbon reservoir in the SDNP soils (34,688.75 Gg C). Taking a conversion rate to valuate the amount of Carbon as an ecosystem service, the total amount reaches US$ 1.3 billion, US$ 2.5 billion and US$ 7.7 billion, respectively, for the environmental compartments. This highlights the enormous and negleted value of soil C stocks in Protected Areas throughout Brazil.

The total carbon stock for each soil class studied in all geoenvironments units is shown in Table III. Both soils class with higher carbon stocks (Haplorthods and Udipsamments) are associated with the highlands of Serra do Divisor, where mountain Podzols occur.

DISCUSSION

Serra do Divisor Complex

The shallow Podzols of the Serra do Divisor have an unusual high organic matter accumulation at the surface (Table I, P1 and P2), and are located at high landscape positions, characterizing a singular soil genesis, distinct from other Podzols elsewhere in the Amazon region, which are typically lowland hydromorphic sandy plains (Lucas et al. 1984LUCAS Y, CHAUVEL A, BOULET R, RANZANI G & SCATOLINI F. 1984. Transição Latossolos-podzóis sobre a formação Barreiras na região de Manaus, Amazônia. Rev Bra Cienc Solo 8: 325-335., Andrade 1990ANDRADE H. 1990. Evolução de uma seqüência de solos argilosos até arenosos no Complexo Guianense da Amazônia. Doctoral thesis, Escola Superior de Agricultura "Luiz de Queiroz"., Mafra et al. 2002MAFRA AL, MIKLÓS AAW, VOLKOFF B & MELFI AJ. 2002. Pedogênese numa seqüência Latossolo-Espodossolo na região do alto rio Negro, Amazonas. Rev Bra Cienc Solo 26: 381-394. https://doi.org/10.1590/S0100-06832002000200012.
https://doi.org/10.1590/S0100-0683200200... , Mendonça et al. 2014MENDONÇA BAF, SIMAS FNB, SCHAEFER CEGR, FERNANDES-FILHO EI, VALE JÚNIOR JF & MENDONÇA JGF. 2014. Podzolized soils and paleoenvironmental implications of white-sand vegetation (Campinarana) in the Viruá National Park, Brazil. Geoderma Re 2-3: 9-20. https://doi.org/10.1016/j.geodrs.2014.09.004.
https://doi.org/10.1016/j.geodrs.2014.09... , 2020).

The accumulation of organic material in the Serra do Divisor highland soils can be attributed to a combination of low nutrient status, high Al levels and deposition of plant residues (most Bromeliaceae) of slow decomposition rate (Mendonça et al. 2020MENDONÇA BAF, FERNANDES-FILHO EI, SCHAEFER CEGR, SIMAS FNB & AMARAL EF. 2020. Genesis and micropedology of soils at Serra do Divisor and Moa river floodplain, northwestern Acre, Brazilian Amazonia. Rev Bra Cienc Solo 44: e0200038. https://doi.org/10.36783/18069657rbcs20200019.
https://doi.org/10.36783/18069657rbcs202... ). Such conditions are quite different from those observed in highlands soils of southeastern Brazil, where organic matter accumulates under lower temperatures (Volkoff et al. 1984VOLKOFF B, CERRI CC & MELFI AJ. 1984. Húmus e mineralogia dos horizontes superficiais de três solos de campo de altitude dos estados de Minas Gerais, Paraná e Santa Catarina. Rev Bras Cienc Solo 8: 277-283., Dias et al. 2001DIAS HCT, FERNANDES-FILHO EI, SCHAEFER CEGR, FONTES LEF & VENTORIM LB. 2001. Geoambientes do Parque Estadual do Ibitipoca, município de Lima Duarte, MG. Revista Árvore 26: 777-786. https://doi.org/10.1590/S0100-67622002000600014.
https://doi.org/10.1590/S0100-6762200200... , Simas et al. 2005SIMAS FNB, SCHAEFER CEGR, FERNANDES-FILHO EI, CHAGAS AC & BRANDÃO PC. 2005. Chemistry, mineralogy and micropedology of highland soils on crystalline rocks of the Serra da Mantiqueira, southeastern Brazil. Geoderma 125: 187-201. https://doi.org/10.1016/j.geoderma.2004.07.013.
https://doi.org/10.1016/j.geoderma.2004.... , Benites et al. 2007BENITES VM, SCHAEFER CEGR, SIMAS FNB & SANTOS HG. 2007. Soils associated with rock outcrops in the Brazilian mountain ranges Mantiqueira and Espinhaço. Rev Bras Bot 30(4): 569-577. https://doi.org/10.1590/S0100-84042007000400003.
https://doi.org/10.1590/S0100-8404200700... ). Some studies (Oliveira 2004OLIVEIRA RR. 2004. Importância das bromélias epífitas na ciclagem de nutrientes da Floresta Atlântica. Acta Bot Bras 18(4): 793-799. https://doi.org/10.1590/S0102-33062004000400009.
https://doi.org/10.1590/S0102-3306200400... , Mantovani & Iglesias 2001MANTOVANI EA & IGLESIAS RR. 2001. Bromélias Terrestres na Restinga de Barra de Maricá, Estado do Rio de Janeiro: influência sobre o microclima, o solo, e a estocagem de nutrientes em ambientes de borda de moitas. Leandra 16: 17-37.) also report the positive influences of bromeliads in capturing organic carbon and nutrient in soils, beside microclimate and water retention. According to Mendonça et al. (2020)MENDONÇA BAF, FERNANDES-FILHO EI, SCHAEFER CEGR, SIMAS FNB & AMARAL EF. 2020. Genesis and micropedology of soils at Serra do Divisor and Moa river floodplain, northwestern Acre, Brazilian Amazonia. Rev Bra Cienc Solo 44: e0200038. https://doi.org/10.36783/18069657rbcs20200019.
https://doi.org/10.36783/18069657rbcs202... , the Serra do Divisor soils have peculiar aspects with high natural organic carbon accumulation, where distinct podzolization process is evident.

The limited extension of this compartment and the highest relative C stocks (Table II), especially for the Ceja Forest geoenvironment, with high accumulation of C in soils at surface and subsurface (Podzols), indicate the high importance of this geoenvironment for the maintenance of organic C in soils. The high biodiversity of this region (Whitemore & Prance 1987, Silveira & Daly 1997SILVEIRA M & DALY D. 1997. Florística e Botânica Econômica do Acre. Relatório Final (1993-1997). UFAC/The New York Botanical Garden/CNPq/NSF, Rio Branco.), closely related with altitudinal variations (Ab’Saber 2002AB’SABER AN. 2002. Bases para o estudo dos ecossistemas da Amazônia brasileira. Revista Estud Av 16(45): 7-30. https://doi.org/10.1590/S0103-40142002000200002.
https://doi.org/10.1590/S0103-4014200200... ) and paleo-environmental conditions (Brasil 1977BRASIL. 1977. Folhas SB/SC. 18 Javari/Contamana; geologia, geomorfologia, pedologia, vegetação e uso potencial da terra. Ministério das Minas e Energia, Rio de Janeiro., Arruda et al. 2018ARRUDA DM, SCHAEFER CEGR, FONSECA RS, SOLAR RRC & FERNANDES-FILHO EI. 2018. Vegetation cover of Brazil in the last 21 ka: New insights into the Amazonian refugia and Pleistocenic arc hypotheses. Global Ecol Biogeogr 27(1): 47-56. https://doi.org/10.1111/geb.12646.
https://doi.org/10.1111/geb.12646... ), and the importance of the submontane tropical forest for hydrological functions (Salati et al. 1983SALATI E, LOVEJOY TE & VOSE PB. 1983. Precipitation and water recycling in tropical rain forests with special reference to the amazon basim. Environmentalist 3: 67-72. https://doi.org/10.1007/BF02240058.
https://doi.org/10.1007/BF02240058... ), all corroborate the great ecosystem service contribution of this unusual mountain environment.

Upper Moa river

The main soils of the Moa floodplain are formed on recent sedimentary deposits (Quaternary). In this sense, sedimentary discontinuities are common due to mixtures of different sediments from upstream sources (Mendonça et al. 2020MENDONÇA BAF, FERNANDES-FILHO EI, SCHAEFER CEGR, SIMAS FNB & AMARAL EF. 2020. Genesis and micropedology of soils at Serra do Divisor and Moa river floodplain, northwestern Acre, Brazilian Amazonia. Rev Bra Cienc Solo 44: e0200038. https://doi.org/10.36783/18069657rbcs20200019.
https://doi.org/10.36783/18069657rbcs202... ). The Ramon and Solimões Formations, for example, are caracterized by pellitic/sandy layers also with occasional limestone interbedding in the upper Moa river (Brasil 1977BRASIL. 1977. Folhas SB/SC. 18 Javari/Contamana; geologia, geomorfologia, pedologia, vegetação e uso potencial da terra. Ministério das Minas e Energia, Rio de Janeiro., Latrubesse et al. 2010LATRUBESSE EM, COZZUOL M, SILVA-CAMINHA SAFDA, RIGSBY CA, ABSY ML & JARAMILLO C. 2010. The Late Miocene paleogeography of the Amazon Basin and the evolution of the Amazon River system. Earth-Sci Rev 99: 99-124. https://doi.org/10.1016/j.earscirev.2010.02.005.
https://doi.org/10.1016/j.earscirev.2010... ). These layers enhance the chemical status of floodplain soils to some extent. The high rainfall in the region promote strong oscillations in water table level and locally leads to ferrolysis process (Brinkman 1970BRINKMAN R. 1970. Ferrolysis, a hydromorphic soil forming process. Geoderma 3: 199-206. https://doi.org/10.1016/0016-7061(70)90019-4.
https://doi.org/10.1016/0016-7061(70)900... ). At the Moa river floodplain the soils are originated with many contrasting soil processes, like clay illuviation, sediment discontinuity, plinthization and redoximorphism (Mendonça et al. 2020MENDONÇA BAF, FERNANDES-FILHO EI, SCHAEFER CEGR, SIMAS FNB & AMARAL EF. 2020. Genesis and micropedology of soils at Serra do Divisor and Moa river floodplain, northwestern Acre, Brazilian Amazonia. Rev Bra Cienc Solo 44: e0200038. https://doi.org/10.36783/18069657rbcs20200019.
https://doi.org/10.36783/18069657rbcs202... ). These soils are richer in nutrients than those from the Serra do Divisor. Based on the literature, chemically-rich, alluvial soils are associated with limestones beds of the Upper Moa, under Open Lowland Ombrophilous Forest with Palms (Brasil 1977BRASIL. 1977. Folhas SB/SC. 18 Javari/Contamana; geologia, geomorfologia, pedologia, vegetação e uso potencial da terra. Ministério das Minas e Energia, Rio de Janeiro., Veloso et al. 1991VELOSO HP, RANGEL FILHO ALR & LIMA JCA. 1991. Classificação da vegetação brasileira adaptada a um sistema universal. IBGE, Rio de Janeiro.).

The paleo-environmental conditions of the upper Moa river valley were drier, leading to younger soils, with eutrophic alluvial plains (Brasil 1977BRASIL. 1977. Folhas SB/SC. 18 Javari/Contamana; geologia, geomorfologia, pedologia, vegetação e uso potencial da terra. Ministério das Minas e Energia, Rio de Janeiro., Schaefer 2013SCHAEFER CEGR. 2013. Clima e paleoclima do Acre: memórias e cenários da aridez quaternária na Amazônia e implicações pedológicas. In: ANJOS LHC, SILVA LM, WADT PGS, LUMBRERAS JF & PEREIRA MG (Eds). Guia de campo da 9ª Reunião Brasileira de Classificação e Correlação de Solos. Brasília: Embrapa, 59-79.). During the Last Glacial Maximum – LGM (21 ka), dry climates changed the structure and composition of Amazonian forest, increasing the deciduous species and openess wetter climates, whereas under wetter conditions at Late Holocene ombrophilous forest prevailed (Arruda et al. 2018ARRUDA DM, SCHAEFER CEGR, FONSECA RS, SOLAR RRC & FERNANDES-FILHO EI. 2018. Vegetation cover of Brazil in the last 21 ka: New insights into the Amazonian refugia and Pleistocenic arc hypotheses. Global Ecol Biogeogr 27(1): 47-56. https://doi.org/10.1111/geb.12646.
https://doi.org/10.1111/geb.12646... ). Dry climates, during the LGM and early Holocene contributed to the genesis of soils with vertic features, carbonates and eutrophy (Brasil 1977BRASIL. 1977. Folhas SB/SC. 18 Javari/Contamana; geologia, geomorfologia, pedologia, vegetação e uso potencial da terra. Ministério das Minas e Energia, Rio de Janeiro.), as reported elsewhere in Acre (Anjos et al. 2013ANJOS LHC DOS, SILVA LM DA, WADT PGS, LUMBRERAS JF & PEREIRA MG (Eds). 2013. Guia de campo da IX Reunião Brasileira de Classificação e Correlação de Solos. Brasília: Embrapa, 204 p.).

According to Brasil (1977)BRASIL. 1977. Folhas SB/SC. 18 Javari/Contamana; geologia, geomorfologia, pedologia, vegetação e uso potencial da terra. Ministério das Minas e Energia, Rio de Janeiro. eutrophic soils with vertic character are predominant (Hapludalfs and Hapluderts) at the upper Moa river valley. Vidalenc (2000)VIDALENC D. 2000. Distribuição das florestas dominadas pelo bambu Guadua Weberbaueri em escala de paisagem no Sudoeste da Amazônia e fatores edáficos que afetam sua densidade. Masters dissertation, Instituto Nacional de Pesquisas Amazônicas. (Unpublished). associated the occurrence of open bamboo forests (Guadua weberbaueri Pilger) in southwestern Amazon with Vertisols, which provide favorable conditions for the occurrence of monodominant forests. The pioneer Bamboo forests are extremely abundant in the southwestern Amazon ranging from 1,500 m altitude in the Andes, down to less than 200 m in the Pucalpa region (Peru), 100 km from the Brazilian border, penetrating the Brazilian territory through the Purus and Juruá rivers, in northwestern Acre (Silveira 2001SILVEIRA M. 2001. A floresta aberta com bambu no Sudoeste da Amazônia: padrões e processos em múltiplas escalas. Masters dissertation, Universidade de Brasília. (Unpublished).).

According to Trumbore & Camargo (2009)TRUMBORE S & CAMARGO PB. 2009. Soil Carbon Dynamics. Amazonia and Global Change 186: 451-462. https://doi.org/10.1029/2009GM000882.
https://doi.org/10.1029/2009GM000882... , eutrophic soils tend to stock less C than dystrophic soils. However, the eutrophic soils of the Forested Hills and Tablelands of the Upper Moa geoenvironment are exceptions, and have thick (until 40 cm) surface horizons rich in organic matter (Brasil 1977BRASIL. 1977. Folhas SB/SC. 18 Javari/Contamana; geologia, geomorfologia, pedologia, vegetação e uso potencial da terra. Ministério das Minas e Energia, Rio de Janeiro.). This condition indicates a high relative C stock for all geoenvironment in this compartment, which has the second highest area and reveals the importance of this ecosystem service.

Middle Moa river

The floristic diversity in this compartment can be directly associated to edaphic variations, both for the expansive character of the clays and for the depth of the soils developed from these sediments (IBGE 1994IBGE. 1994. Projeto de Proteção do meio Ambiente e das Comunidades Indigenas. Diagnóstico Geoambiental e Socioeconomico: Área de Influencia da BR-364 trecho RioBranco/Cruzeiro do Sul. IBGE/IPEA, Rio de Janeiro.). The low C stock of this compartment may be indirectly associated with higher soil fertility compared to other soils, which favors microbiological activity and organic carbon mineralization, in spite of the higher levels of clay material of these soils, that favor the direct protection of the organic carbon (Wiseman & Püttmann 2006WISEMAN CLS & PÜTTMANN W. 2006. Interactions between mineral phases in the preservation of soi organic matter. Geoderma 134: 109-118. https://doi.org/10.1016/j.geoderma.2005.09.001.
https://doi.org/10.1016/j.geoderma.2005.... ). In addition, the geomorphological condition of the aluvial soils favors the erosion losses of the surface horizons, richer in organic carbon, leading to lower C. However, the soil stock carbon relevance of this compartment is related to its large area, where nutrient cycling is a key aspect of maintenance of organic C.

The neotectonic movements responsible for the uplift of the Serra do Divisor (Moa, Rio Azul and Divisor Formations) also promoted the relative subsidence of the surface near the Serra, following the same N-S alignment, forming a footslope depression (Brasil 1977BRASIL. 1977. Folhas SB/SC. 18 Javari/Contamana; geologia, geomorfologia, pedologia, vegetação e uso potencial da terra. Ministério das Minas e Energia, Rio de Janeiro.). This depression, due to its conditions of high accumulation of sandy material in low-lying areas of the landscape, near the drainage channels, is a favorable environment for the open palm forest formations, especially Buriti (Mauritia flexuosa). According to Moura & Wanderley (1938)MOURA P & WANDERLEY A. 1938. Noroeste do Acre: reconhecimentos geológicos para petróleo. DNPM, Rio de Janeiro. the sediments brought by the mountain range encroach on large deposits and can bury part of the local vegetation, predominantly of the genus Mauritia, often changing the levels of the water table and producing true Buritis cemeteries. These sandy soils show the highest relative C stocks in this compartment, over a limited extension, not mapped in our study.

The main sediments transported by the river Moa and tributaries originate from the valleys of the upper Moa river and structural valleys of the Serra do Divisor. However, according to Archibald & King (1985)ARCHIBALD PA & KING JM. 1985. The algal flora of two distinct habitats along the Moa rivers in the State of Acre, Brazil. Acta Amazônica 15(1-2): 145-151. https://doi.org/10.1590/1809-43921985155152.
https://doi.org/10.1590/1809-43921985155... , the Moa River receives large quantities of organic acids from the superficial and subsurface flows of podzolized soils of Serra do Divisor, being classified as a river of black waters and with low mineral content. This considering could indicate a probable contribution of the C inputs in the Fluvial Plain geoenvironment and increasing the ecosystem service importance o C stock.

CONCLUSIONS

The soils and geoenvironmental units of SDNP were mapped and characterized allowing to estimate the soil carbon stock as a key aspect of the ecosystem services in both aspects. The Serra do Divisor shows a unique subandean environments in Brazilian Amazonia, with the occurrence of Ceja forest on sandy soils, and high accumulation of surface organic carbon.

The soils developed on sandstone in the Serra do Divisor show an expressive accumulation of organic material in the superficial horizons, and active podzolization, leading to enhanced carbon stocks in soils. The Middle Moa river has the highest total C reservoir in the soil of the northern sector of the SDNP, due to a large extension. In the Upper Moa river, eutrophic, nutriente-rich soils are reported to Amazon region, but still lack more detailed studies. This Protected Area holds a large soil carbon stock, and a valuable asset in terms of future valuation of this key soil ecosystem service.

ACKNOWLEDGMENTS

To the Program of the Amazon Region Protected Areas (ARPA), ICMBio Cruzeiro do Sul (Acre), Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), Conselho Nacional de Desenvolvimento Cientifico e Technológico (CNPq) and Núcleo de Estudos de Planejamento e Uso da Terra (NEPUT) / Universidade Federal de Viçosa (UFV).

REFERENCES

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