Vegetational changes during the last millennium inferred from a palynological record from the Bananal Island, Tocantins, Brazil

• Published in: Acta amazonica 2015-06, Vol.45 (2), p.215-230
• Main Authors: Mendes, Lais Aguiar da Silveira, Pires, Etiene Fabbrin, Meneses, Maria Ecilene Nunes da Silva, Behling, Hermann
• Format: Article
• Language: Portuguese
• Subjects: Moraceae; Urticaceae
• ISSN: 0044-5967; 1809-4392
• DOI: 10.1590/1809-4392201402265

SThe Bananal Island is regarded the largest fluvial island in the world, bounded by Araguaia and Javaes rivers, being located in southwest of Tocantins. The objectives of this work were to provide information about the vegetational changes that occurred at the Bananal Island, in order to contribute to the understanding the dynamics of past and current savanna and areas of ecotones with forests. Thus, a sedimentary core collected from a small lake at the Bananal Island plain was submitted to pollen and radiocarbon dating analyses. The results showed that the last millennium was dominated by forest reflecting a wet climate. At the beginning of the record (920-770 yr cal BP) the wet climate and high rainfall produced flooding during long rainy seasons that maintained the Javaes River connected to the studied lake, and hence, this environment was marked by the presence of a homogenous forest rich in Moraceae/Urticaceae, due to flooded soils occurrence. During the following period (770-304 yr cal BP) the reduced rainfall and shortening of the rainy seasons isolated the lake from the Javaes River for long periods, which caused a diversification of the forest and gave rise to the appearance of the components of floodplain forest and marsh vegetation adapted to waterlogged soils. Since 304 years cal BP to the present day this environment remained dominated by this diverse forest and the lacustrine conditions were also similar to previous phase, with a slight increase of moisture in the last 84 years that caused the increase of Piranhea.Original Abstract: A Ilha do Bananal e considerada a maior ilha fluvial do mundo, margeada pelos Rios Araguaia e Javaes, sendo localizada na porcao sudoeste do Estado do Tocantins. Os objetivos deste trabalho foram obter informacoes sobre as mudancas na vegetacao ocorridas na Ilha do Bananal, de forma a contribuir para o entendimento da dinamica preterita e atual da vegetacao de cerrado e areas de ecotonos com floresta. Assim, um testemunho sedimentar coletado em um pequeno lago na planicie da Ilha do Bananal foi submetido as analises polinica e de datacao por radiocarbono. Os resultados mostraram que o ultimo milenio foi dominado por floresta refletindo um clima umido. No inicio do registro (920-770 anos cal AP) o clima umido e a alta pluviosidade produziram inundacoes durante longos periodos chuvosos que mantiveram o rio Javaes conectado ao lago estudado, e assim, este ambiente foi marcado pela presenca de uma floresta homogenea r