Fire history of Patagonia: clima te versus human cause

Resumo

Human society's concern about future environmental changes in response to both natural forcings, such as climate, and ever increasing human impact can only be addressed if the interaction between the natural and man-made forcings are fully understood. One parameter that lends itself for such analysis is fire. The historical record is toa short and ambiguous to provide data adequate to discriminate between natural and man-induced changes in fire frequencies. Paleoenvironmental records, inclusive of both the historic and the prehistoric past, can provide an appropriate data set with which to address this question. These data include paleoclimate reconstructions, pollen, and charcoal records from dated sediment sections, and information on past human impact derived from historical and archaeological evidence. The Patagonian region is well suited for such a study because of its climatic diversity, its wide range of ecosystems, and the adaptation of its ecosystems to fire. Records from latitudes 36º to 55ºS suggest that although prehistoric human activities may have amplified extent of fires, climate played the central role. Changes in patterns of climate variability were particularly important. Whenever variability was high, during the late glacial and the late Holocene, fires were abundant. Late glacial variability is probably related to fluctuations in the extent of Antarctic sea-ice which in turn influences the latitudinal position of the westerly stormtracks; late Holocene variability, on the other hand, is related to the influence of El Niño/Southern Oscillation