FIGURE 16 Representative pollen diagrams from the northern Andes: Laguna Fuquene (van Geel and van der Hammen, 1973), La Primavera (Melief, 1985), and Laguna Huatacocha (Hansen et al., 1984).

proportion of drought- and disturbance-adapted taxa than are present today. In the forests west of the Andes, Nothofagus parkland was more extensive than it is today, with high proportions of Weinmannia and other open-forest and disturbance taxa; whereas east of the Andes, substantial numbers of steppe taxa codominat-ed with Nothofagus dombeyi-type, and charcoal particles are abundant in sediments from this period. The climate at the middle latitudes must have been warmer and seasonally drier than it is today (Villagran, 1995; Markgraf, 1991b). At latitudes 45°-50°S, maximum development of Patagonian rain forest and Magellanic moorland occurred west of the Andes in the early

Holocene (Lumley and Switsur, 1993; Ashworth et al., 1991), and lake levels were high east of the Andes (Stine and Stine, 1990). At high southern latitudes south of 50°S, Nothofagus woodland and a high fire frequency characterized the early Holocene (Markgraf and Anderson, 1994; Huber and Markgraf, in press; Heusser, 1999). The Harberton record (Fig. 17) illustrates this trend, which suggests that climate must have been seasonally drier and more variable than it is today. During the early Holocene, the westerly storm tracks that determine precipitation patterns in the temperate region must have been more narrowly focused between 45° and 50°S, leaving the regions both to the north and

Holocene Vegetation and Climate Variability in the Americas

Holocene Vegetation and Climate Variability in the Americas

Mallín Aguado

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