Post-glacial vegetation in the South Patagonian territory of the giant ground sloth, Mylodon

By comparison with the major modern plant communities of southern Patagonia, the changing post-glacial vegetation of the region is reconstructed from macrofossils derived from deposits in the Cueva del Mylodon, Ultima Esperanza, S. Chile. The oldest deposits, carbon-dated as c. 12,400 B.P., comprise dung of the extinct ground sloth Mylodon darwinii and show the animal to have fed entirely on Cyperaceae, Gramineae and species associated with these in the modern cool, wet sedge-grasslands of western Patagonia, communities which would be expected after the retreat of the ice. Overlying deposits of well-preserved, wind-blown leaf-litter permitted some quantitative analyses which show a rise of evergreen forest dominated by Nothofagus betuloides that reached its maximum c. 7000 B.P. and then declined as it was replaced by deciduous N. pumilio forest. A break in the fossil plant record, covering the human occupation about 5643 B.P. and the subsequent final appearance of Mylodon remains, is followed by evidence of mixed evergreen/deciduous forest in which Nothofagus pumilio gradually increases in importance to give deciduous forest some 2500 years ago similar to that found in the environs of the cave in historical times. Comparison with pollen diagrams shows that the modern climatic and vegetation difference between E. Fudgia and Ultima Eeperanza has persisted throughout the post-glacial period.