Vegetation and environmental changes in Extra-Andean Patagonia, Argentina

MANCINI, MARÍA VIRGINIA; BAMONTE, F.P.; MARCOS, M.A.

Valle Uco

Conferencia; 4th Southern Deserts Conference; 2014

Laboratorio de Paleo-Ecología Humana FCEN-UNCUYO

Extra-Andean Patagonia is a large region with arid and semiarid climatic conditions. Mean annual precipitation is lower than 200 mm due to the rainshadow effect produced by the Andes. Spatial variation of rainfall is one of the causes of vegetation patchiness which is represented by grass, shrub ,and dwarf-shrub steppes. Modern pollen?vegetation?climate relationships from different precipitation gradients were established as analogs to understand Holocene vegetation dynamics. According to the current correlation between precipitation and wind speed, changes revealed by the pollen records are interpreted as indicative of variations in the intensity and/or position of the westerlies; the influence of Atlantic moist air is more pronounced toward the east. These atmospheric circulation changes led to drifts of the foreststeppe ecotone and in steppe composition. Paleoenvironmental reconstructions are based on pollen records comparison from different depositional environments such as ?mallines,? lakes and archaeological sites (caves and rockshelters). Palynology of archaeological contexts generates essential information that properly combined and integrated can improve the understanding of past landscapes. An important consideration is the stratigraphic resolution of archaeological sequences. Comparison of fossil pollen records from archaeological sites and those analyzed from other deposits strengthen paleoclimatic reconstructions, can be used to assess similarities and differences in the distribution patterns of vegetation and their relationship with regional (climate) and/or local (topography, substrate, disturbance) changes. Environmental reconstruction presents similar trends during the Pleistocene?Holocene transition. Human occupation beginning in the Late Pleistocene and early Holocene in the southern steppe suggests that humans utilized the area during times of increased moisture. Major human impact on vegetation began around 150 years ago with the European settlement; overgrazing led to changes specially in the grass steppe. The agreement between these trends and other paleoenvironmental interpretations based on pollen, charcoal, and sedimentological records suggests that the reconstructed features reflect large-scale climatological patterns over Patagonia. However, stratigraphical and chronological discontinuities, with unrepresented processes, limit knowledge of past environmental change. A few continuous lacustrine records of the climatic and ecological history are available for southernmost Patagonia. Other paleoenvironmental reconstructions are needed to achieve a better understanding of the regional changes that make it possible to identify climatic events and to contribute new insights to the role of atmospheric circulation at these latitudes. For these reasons, the following is recommended for future studies: increasing high resolution paleoecological records and analyzing continuous sequences of the steppe to compare with available reconstructions.