European impact on fire regimes and vegetation dynamics at the steppe-forest ecotone of southern Patagonia

A macroscopic charcoal, pollen and peat macrofossil record from Rio Rubens Bog in southern Patagonia, covering the last c. 1200 years, provides detailed evidence concerning European impact on veg etation and fire frequency. Based on 210Pb and ¹⁴C chronologies, we demonstrate that thefirst introduction of the weed Rumex acetosella occurred during early European contact in the sixteenth century or shortly thereafter. Thus, the first occurrence of this pollen type should not be used as a time marker for permanent European settlement in the late nineteenth to early twentieth centuries. Local fires did not occur for more than 900 cal. yr prior to European contact, and became frequent, with fire-return intervals on the order of 100 cal. yr, after c. ad 1600. Without an independent chronology, the onset of high fire activity would have been erroneously attributed to the initiation of European settlement in the late nineteenth century, based on the presence of Rumex acetosella. The coincidence between weed introduction and fires, in combination with wet climate, favours a change in human ignition frequency as the driving factor for frequent fires after c. ad 1600. We speculate that Europeans may have impacted fire frequency by indirectly influencing aboriginal hunting through the introduction of horses. Whereas changes in forest vegetation during early European contact were small, subsequent European settlement initiated a period of severe forest destruction through burning, logging and grazing. The most rapid and severe phase of deforestation has been associated with large-scale, export-orientated logging since the 1980s.