Historia paleoambiental del ecotono bosque-estepa al interior del Parque Nacional Torres del Paine ( Región de Magallanes , Chile)durante los últimos 14.800 años

Abstract

In this thesis, a pollen and charcoal high resolution record (45 and 20 years between samples, respectively) was developed from lacustrine sediments obtained from Lago Guanaco (51'52'3-72" 52' W, 180 m.s.n.m.), located in the forest-steppe ecotone into the Torres del Paine National Park. The aim of this thesis was to reconstruct the vegetation, clirnate, and fire history of Southem Patagonia, in order to answer these questions: What is the chronology and direction climate changes during the Holocene in Southem Patagonia?, Were these changes gradual or abrupt? How did the fire history in the forest-steppe ecotone during the Holocene?, Exist a climatic and/or vegetacional stage than more related with the occurrence of periodic fres?, How compare the chronology of Southem Patagonia (Torres del Paine), with other evidence of climatic changes from Northem Patagonia (Lake District-Chiloe island) and the neoglacia-l chronologies? The record from Lago Guanaco suggests colder conditions, limiting the development of vegetation between 14,8-12,6 ka (ka:103 calendar years BP). At 12.6ka occurs ari increase in the temperatures, allowing the establishment of a steparian vegetation, but cold conditions persist until ll,5 ka. Between 11,5-7,8 ka high percentages values of Poaceae and Asteraceae are recorded. A sustained increase in the percentages of Nothofags is clear between 7,8-6,9 ka, indicating a shift of the taxon to the study area tmder humidity conditions. This change in the landscape culminates in the establist¡nent of a shrub steppe at 4,8 ka. A brief pulse of increase n the Nothofagus percentages between 4,8-3,8 k4 demarcating the transition towards a more heterogeneous vegetational landscape, with the emergence of new taxa in the record: Apiaceae, Plantago and Phacelia. Relatively low frequency of fires occur during the development of the shrub-steppe environments previously described, suggesting restrictions associated with the accumulation of combustible material. An abrupt (<50 years) increased the percentages of Nothofogus occurs around 2,9 ka, and demarcates the establishment of wood/shrub vegetation similar to the pre-Andean scrubland, indicating an increase in the hydric availability. An increase in the fire frequency, recorded in simultaneity with this change in the vegetational landscape, suggest lower restrictions on the accumulation/availability of fuel material. Maximum values of Nofhofogus percentages were observed between 570-70 cal BP, indicating the establishment of forest in the study area under a new inc¡ease in the precipitation. A decrease in fire frequency is recorded at a similar age, suggesting reshictions regarding availability of fuel. The development of current steppe landscape in the area of the park is established around 1894 AD, simultaneously with the expansion of Rumex cf. acetosella (an exotic European specie), indicating a vegetational landscape change under anthropogenic action. The similarity between the timing of the inferred climatic changes in the Lago Guanaco, Lago Condoriúo (Lake District) pollen records, and the chronologies of neoglacial advances of Southern Patagonia" suggest changes in position and flow of the Southem Westerlies at millennial and multi-millennial time scales.