Climate and local controls of long-term vegetation dynamics in northern Patagonia (Lat 41°S)

Patagonian vegetation has dramatically changed in composition and distribution over the last 16,000. yr. Although patterns of vegetation change are relatively clear, our understanding of the processes that produce them is limited. High-resolution pollen and charcoal records from two lakes located at lat 41°S provide new information on the postglacial history of vegetation and fire activity at the forest-steppe ecotone, and help clarify the relative importance of local and regional drivers of late-Holocene ecological change. Our results suggest that late-glacial parkland was colonized by shrubs at ca. 11,200. cal. yr BP and this vegetation persisted until 4900. cal. yr BP, when increased humidity allowed for the establishment of Nothofagus forest. The late Holocene is characterized by oscillations in forest dominance largely driven by changes in humidity, possibly associated with the onset or strengthening of ENSO. In the last 4900. yr, humid periods (4900-3800 and 2850-1350. cal. yr BP) have promoted Nothofagus forest, whereas drier times (3800-2850 and 1350-450. cal. yr BP) have favored Austrocedrus expansion. At intermediate moisture levels, however, the lower forest supported both taxa, and fire became an important control of community composition, with severe, infrequent fires facilitating Nothofagus regeneration and high fire frequency and intensity supporting Austrocedrus.