Reconstituição paleoambiental a partir do sinal fitolítico na ESEC Caetetus – Gália (SP)

Abstract

The truthful reconstruction of vegetation is essential for understanding historical trajectories of climate change, and to address the nature and extent of anthropic impact on the ecosystems. Studies on phytolyths, especially those related to the production, variations in shape and size of these biomineralizations, and interpretation of the phytolith assemblage preserved in soils and sediments, have contributed to the understanding of paleoenvironmental variations, especially during the Quaternary Period, in various parts of the world. In this research the phytolith analysis was applied in an environmental preservation ara of the Semideciduous Seasonal Forest - SSF, located in the interior of the Estação Ecológica of Caetetus (ESEC Caetetus), in Gália, State of São Paulo. The study was carried out using a multiproxy approach aiming and a set of interrelated and complementary data had as objective to organize the reference collection of modern phytolyths (RCMP) of SSF and to understand the evolutionary and chronological trajectory of the vegetation of the area of ESEC Caetetus, in the Western Plateau Paulistas, during the Holocene, aiming to contribute to the understanding of the climatic and vegetation history of the region, subsidy for the preservation of this forest fragment. Samples of plants and soil were collected along a 500 meter transect in the interior of the forest. Phytoliths were extracted from plant and soil samples to understand the phytoliths production of FES to reconstruct the trajectory of vegetation along the Holocene in the area. In addition, analyses of carbon isotopes, dating of soil organic matter and physical and chemical analysis of soil were performed to characterize the means of preservation of phytolyths. The assemblage obtained in each plant species and in the soil was observed in petrographic microscope (40X), photographed, measured, described and named according to ICPN 1.0. We counted 300 morphotypes with identifiable form, greater than 5μm for plant samples and 200 morphotypes in soil samples. For this set, 10,668 phytoliths were counted and 46 morphotypes were identified. 61% of the samples presented abundant production, indicating high potential for FES phytolith production. The eudicotiledone samples presented high multiplicity. The globular (psilate and roughness) and polygonal blocks morphotypes were the most redundant in the analyzed set. No new morphotype with taxonomic significance at the family level was found. The indexes used were the same as suggested by several authors, only the D/P index was adapted, considering the globular morphotypes psilate and rugose for arboreal density. The reconstitution of the ESEC vegetation allowed identifying that during the lower Holocene in the area a more open than current vegetation prevailed, which during the middle Holocene suffered an even greater opening, associated with a drier and warmer period than the previous one, which would have allowed the formation of vegetation like a Cerrado/Cerradão, with an important contribution of woody plants. The current Semidecidual Seasonal Forest would have started its formation around 1.400 years AP.