Late Quaternary grassland (Campos), gallery forest, fire and climate dynamics, studied by pollen, charcoal and multivariate analysis of the São Francisco de Assis core in western Rio Grande do Sul (southern Brazil)
Introduction
Several palaeoecological studies from the Campos and Araucaria forest regions of the southern Brazilian highlands have been carried out in the last decade. Data from the states of Paraná (Serra Campos Gerais: Behling, 1997), Santa Catarina (Serra do Rio Rastro, Morro da Igreja, Serra da Boa Vista: Behling, 1993, Behling, 1995) and Rio Grande do Sul (Aparados da Serra: Roth and Lorscheitter, 1993; São Francisco de Paula: Behling et al., 2001; Cambará do Sul: Behling et al., 2004) have proven that extensive areas of Campos vegetation existed on the highlands through glacial, early and mid Holocene times. The dominance of Campos vegetation was attributed to cold and dry glacial, and warm and dry early Holocene climates. A dry season lasting probably about 3 months per year was characteristic for the early and mid Holocene period (Behling, 1997, Behling, 2002). Initial expansion of Araucaria forests started by migration from the gallery forests along the rivers about 3210 cal yr BP, which indicates a turn to somewhat wetter climates. A marked expansion of Araucaria forests started on the highlands, replacing Campos vegetation in Santa Catarina State about 930 cal yr BP ago, and in Paraná State (Serra Campos Gerais) about 1400 cal yr BP ago, reflecting a very humid climate without a marked seasonal dry period. New data from the 42,000 14C years BP old Cambará do Sul record indicate that the initial expansion of Araucaria forests started by 4320 cal yr BP, and the marked expansion by 1100 cal yr BP (Behling et al., 2004).
So far, nothing was known about the vegetation and climate history of the Campos region in the lowlands of Rio Grande do Sul State west and south of the highland plateau. Our main questions are: Is the Campos formation the natural vegetation of the southern lowland? Do we have similar climate changes in the southern lowlands, compared to the southern highlands? What would be the effect of climate change on the southern lowland vegetation? What was the fire history in the lowland? How and when began the pre-Columbian occupation in the lowland?
To investigate the late Quaternary vegetation, climate and fire dynamics, we cored a peat bog in the São Francisco de Assis region of western Rio Grande do Sul state. The site is interesting for at present it is surrounded by grassland characteristic for the western part of Rio Grande do Sul State, close to gallery forest and not far from the edge of the forest on the westernmost escarpments of the southern Brazilian highlands.
Section snippets
Geographical setting
The lowlands of Rio Grande do Sul (Fig. 1) lie at elevations between 40 and 200 m south and west of the South Brazilian highlands and north of the crystalline shield. The lowland is a soft rolling landscape, and includes some higher elevated hills. Major rivers are the Ibibuí, draining westward to the Uruguay River, and the Jacuí River, draining eastward to the Patos Lagoon and the Atlantic Ocean. More information on the geography of the region can be found in Rambo (1956) and in satellite
Methods
The peat deposit was cored in its deepest part using a Russian corer. From bedrock, the total length of the core was 380 cm. Sections of 50 cm length were extruded on-site, wrapped in plastic and aluminum foils and stored under cool (ca. +4 °C) and dark conditions after return from the field and before sampling. For radiocarbon dating, 1-cm slices of bulk subsamples were taken. Organic matter was dated through AMS at the laboratory of the University Nürnberg-Erlangen (Germany).
For pollen
Stratigraphy
The core is underlain by compact clayish sandy. From the base from 380 to 370 cm, sandy gray clay is found (Fig. 3). Between 370 and 265 cm, brown-gray clay with organic matter accumulated. From 265 to 175 cm compact, completely decomposed black organic matter accumulated. From 175 to 110 cm, the sediment is composed of dark brown to black, very compact, completely decomposed organic material, containing rootlets. Between 110 cm and the grassy surface, the deposit is brown, weakly decomposed
Interpretation and discussion
The pollen analytical results from the São Francisco de Assis record document that the lowlands in eastern Rio Grande do Sul State were naturally covered by Campos vegetation during full- and lateglacial periods (zone SFA-I). Gallery forests, forming today along the rivers did not exist at that time. The evidence of only a few pollen grains belonging to gallery forest taxa may suggest a few isolated trees or shrubs along the rivers. The climate was relatively dry and too cold to form gallery
Conclusion
The pollen and charcoal records from São Francisco de Assis reveal for the first time evidence for palaeoenvironmental changes in of the southern Brazilian lowland since the last glacial maximum. Four AMS radiocarbon dates provide time control for the about 22,000 cal yr BP old pollen record.
Pollen data document that the lowland of western Rio Grande do Sul State was covered with natural Campos vegetation throughout the recorded glacial and postglacial period. Modern gallery forests did not
Acknowledgments
We are grateful to Carlos Alberto Silveira (owner of Itajuru Farm), Fernando Quadros and José Pedro Trindade for providing invaluable assistance in the field, and László Orlóci for suggestions on the manuscript. The authors thank Vera Markgraf, Marie-Pierre Ledru and one anonymous reviewer for providing constructive comments. The project was supported by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq; Brazil) with a research grant and fellowship given to Valério De Patta
References (37)
Late Quaternary vegetation, climate and fire history in the Araucaria forest and Campos region from Serra Campos Gerais (Paraná), S. Brazil
Rev. Palaeobot. Palynol.
(1997)South and Southeast Brazilian grasslands during Late Quaternary times: a synthesis
Palaeogeogr. Palaeoclimatol. Palaeoecol.
(2002)- et al.
Holocene environmental changes from the São Francisco de Paula region, southern Brazil
J. South Am. Earth Sci.
(2001) - et al.
Late Quaternary Araucaria forest, grassland (Campos), fire and climate dynamics, studied by high resolution pollen, charcoal and multivariate analysis of the Cambará do Sul core in southern Brazil
Palaeogeogr. Palaeoclimatol. Palaeoecol.
(2004) CONISS: a Fortran 77 program for stratigraphically constrained cluster analysis by the method of the incremental sum of squares
Comput. Geosci.
(1987)The fundamentals of vegetation change—complexity rules
Acta Biotheor.
(2000)- et al.
Chaotic dynamics in a multispecies community
Environ. Ecol. Stat.
(1997) - Behling, H., 1993. Untersuchungen zur spätpleistozänen und holozänen Vegetations-und Klimageschichte der tropischen...
Investigations into the late pleistocene and Holocene history of vegetation and climate in Santa Catarina (S Brazil)
Veg. Hist. Archaeobot.
(1995)Campos do Rio Grande do Sul: caracterização fisionômica e problemática ocupacional
Bol. Inst. Biociênc. UFRGS
(1997)
Distribuição geográfica das disponibilidades hídricas do solo possíveis de ocorrerem no estado do Rio Grande do Sul
Rev. Cent. Ciênc. Rurais
Earliest hunters and gatherers of South America
J. World Prehist.
Textbook of Pollen Analysis
Origens da ocupação pré-histórica do Rio Grande do Sul na transição Pleistoceno–Holoceno
Paleopaisagens e povoamento pré-histórico do Rio Grande do Sul
Southern Brazilian phytogeographic features and the probable influence of upper quaternary climatic changes in the floristic distribution
Bol. Parana. Geociênc.
Ecologia da flora e vegetação do Vale do Itajaí (Continuação)
Sellowia
Numerical Ecology
Cited by (173)
Pleistocene–Holocene climatic events on the inner coastal plain of southernmost Brazil in relation to marine isotopic stages
2024, Journal of South American Earth SciencesGeoarchaeology of open-air sites of the Foz do Chapecó area in the upper Uruguay river, southern Brazil
2024, Quaternary Science ReviewsPaleobiology of Pleistocene large land mammals from the Brazilian Pampa
2023, Quaternary InternationalSoil-landscape-vegetation relationships in grassland-forest boundaries, and possible applications in ecological restoration
2023, Journal of South American Earth SciencesPalynology of sedimentary soils in the Pampa biome: Grassland-forest mosaics and landscape-soil-pollen relationships
2023, Journal of South American Earth SciencesLandscape changes in the Campos region, southernmost Brazil, since the early deglaciation based on a multi-proxy analysis of a peat bog
2023, Palaeogeography, Palaeoclimatology, Palaeoecology