Abstract

Despite several investigations on the long-term vegetation dynamic of the eastern side of the Andes, our knowledge is still limited, especially in northern Patagonia where the forest near the steppe ecotone is particularly divers. The distribution of the vegetation in this area responds to a west-to-east precipitation gradient, documenting that climate is the main control on the regional-scale variability in vegetation composition. However, natural and anthropogenic disturbances amplify or override the effects of climate on vegetation composition. Therefore, understanding the regional drivers, such as fire, volcanic eruptions and human activity and differentiating them from climate is important for climate reconstructions and nature conservation efforts. The aims of this project are to (i) reconstruct the late Holocene environmental history, (ii) identify the principal local and regional drivers of vegetation changes, (iii) compare the effect of disturbance events between sites at different altitudinal positions, and (iv) examine the fire-climate interaction across time. To answer these questions, we collected sediment cores from two lakes: Lake Bruja (40°14’S, 71°30´W; 1069m) and Lake Avutarda (40°23’S, 71°25´W; 1610m). Lake Bruja is situated about 150 m above a wide valley which is used for summer pasture of cows and horses that roam the forest around the lake, which is dominated by Nothofagus dombeyi and Nothofagus obliqua. Coring stopped after 130 cm due to a thick tephra deposition and the base of the core was dated to 3600 years ago. Lake Avutarda is located near the treeline of Nothofagus pumilio. Here a 110 cm long core was obtained and the bottom dated to 2800 years ago. Pollen and charcoal analysis, lithological description and estimation of organic matter content by loss on ignition were carried out on both cores. Preliminary results show frequent deposits of tephra, derived from volcanoes, mostly located in Chile. We are comparing the impact of these tephra depositions as well as fire events between the two sites. This work will contribute to an understanding of the importance of disturbance for the vegetation composition and help reconstruct changes in Holocene climate near the forest steppe ecotone in Patagonia.