From ice age to modern: a record of landscape change in an Andean cloud forest

To investigate the palaeoecological changes associated with the last ice age, subsequent deglaciation and human occupation of the central Andes. Lake Pacucha, Peruvian Andes (13°36′26″ S, 73°19′42″ W; 3095 m elevation). Vegetation assemblages were reconstructed for the last 24 cal. kyr bp (thousand calibrated ¹⁴C years before present), based on pollen analysis of sediments from Lake Pacucha. An age model was established using ¹⁴C accelerator mass spectrometry dates on bulk sediment. Fossil pollen and sedimentological analyses followed standard methodologies. Puna brava replaced the Andean forest at the elevation of Lake Pacucha at the Last Glacial Maximum (LGM). Deglaciation proceeded rapidly after 16 cal. kyr bp, and near-modern vegetation was established by c. 14 cal. kyr bp. The deglacial was marked by the range expansion of forest taxa as grassland taxa receded in importance. The mid-Holocene was marked by a lowered lake level but relatively unchanged vegetation. Quinoa and maize pollen were found in the latter half of the Holocene. Temperatures were about 7-8 °C colder than present at this site during the LGM. The pattern of vegetation change was suggestive of microrefugial expansion rather than simple upslope migration. The mid-Holocene droughts were interrupted by rainfall events sufficiently frequent to allow vegetation to survive largely unchanged, despite lowering of the lake level. Human activity at the lake included a 5500-year history of quinoa cultivation and 3000 years of maize cultivation.