Fire and vegetation dynamics of endangered Araucaria araucana communities in the forest-steppe ecotone of northern Patagonia

Abstract

Recent changes of the fire regime in northern Patagonia may have reduced populations of Araucaria araucana, which is listed as an endangered species. Although Araucaria does not depend on fire to persist, natural fires are part of the ecosystem and Araucaria withstands moderate fires. To understand recent and long-term vegetation patterns and processes that help in conservation tasks, we reconstructed the vegetation and fire history of the forest-steppe ecotone over the last 9 kyr based on a well-dated sediment core obtained from Lake Relem in northern Patagonia. Before 4.5 ka, pollen content indicates that steppe vegetation dominated the landscape. Pollen composition after 4.5 ka suggests that steppe was gradually replaced by scrublands and woodlands. The highest amount of Nothofagus woodland cover was reconstructed for the last 2.5 kyr. A continuous record of macro-charcoal particles indicates 20 fire events of low magnitude, with more frequent fires between 6 and 2.5 ka. Changes in vegetation composition were partly related to fire frequency changes, while the magnitude of fire events had no detectable influence on the vegetation. Pollen from the endangered Araucaria documents that the species was widespread around Lake Relem between 8 and 6 ka, decreasing abruptly ~6 ka, and slightly increasing up to the present. Results do not show a change in the fire regime due to the Euro-American colonization. The long-term trend of this Araucaria population does not show the decline observed elsewhere.