LATE QUATERNARY FOREST - STEPPE CONTACT ZONE, ISLA-GRANDE-DE-TIERRA-DEL-FUEGO, SUB-ANTARCTIC SOUTH-AMERICA

The forest-steppe ecotone, stretching across the Atlantic slope of Isla Grande de Tierra del Fuego in its present-day configuration, apparently developed within recent centuries. This conclusion is reached from assessment of fossil pollen and charcoal records obtained from radiocarbon-dated sections of mires located in proximity to the forest boundary. At Onamonte (53-degrees-54'S, 68-degrees-57'W), in the north-central part of Isla Grande, pollen frequency and influx data of trees (Nothofagus) recorded at 5-cm intervals in sections over the past > 1 2,000 years imply a landscape of extended steppe until trees began to invade around 5000 BP. Low influx of Nothofagus in the early Holocene is probably the result of pollen coming from a distant source; alternatively, fire may have ben a contributory factor for the low levels of influx recorded. The first significant increase of Nothofagus, believed to be from woodland at Onamonte, occurred 1500 years ago. Only after 500 BP is forest development evident from unprecedented, large quantities of Nothofagus. At this time, the forest-steppe boundary reached its northernmost position on Isla Grande. Setbacks in the overall advance of trees are attributed to climatic change, fire, and competition between Nothofagus and Empetrum heath. In contrast to the situation in Patagonia, burning during European settlement was limited.