A vegetation and fire history of Lake Titicaca since the Last Glacial Maximum

Fine-resolution fossil pollen and charcoal analyses reconstruct a vegetation and fire history in the area surrounding Lake Titicaca (38 10 in, Peru/Bolivia) since ca. 27 500 cal yr BP (hereafter BP). Time control was based on 26 accelerator mass spectrometer (AMS) radiocarbon dates. Seventeen AMS dates and 155 pollen and charcoal samples between ca. 17 500 BP and ca. 3 100 BP allow a centennial-scale reconstruction of deglacial and early- to mid-Holocene events. Local and regional fire signals were based on the separation of two charcoal size fractions, greater than or equal to180 mum and 179-65 mum. Charcoal abundance correlated closely with the proportion of woody taxa, present in the pollen spectra. Little or no pollen was detected in the sedimentary record prior to ca. 21000 BP. Very cold climatic conditions prevailed, with temperatures suggested to be at least 5-8degreesC cooler than present. Increases in pollen concentration suggest initial warming at ca. 21000 BP with a more significant transition toward deglaciation ca. 17 700 BP. Between 17 700 BP and 13 700 BP, puna brava is progressively replaced by puna and sub-puna elements. The most significant changes between the Pleistocene and the Holocene floras were largely complete by 13 700 BP, providing an effective onset of near-modern conditions markedly earlier than in other Andean records. Fire first occurs in the catchment at ca. 17 700 BP and becomes progressively more important as fuel loads increase. No evidence is found of a rapid cooling and warming coincident with the Younger Dryas chron. A dry event between ca. 9000 BP and 3100 BP, with a peak between 6000 and 4000 BP, is inferred from changes in the composition of aquatics, and the marsh community as pollen of Cyperaceae is replaced by Poaceae, Apiaceae, Plantago and the shrub Polylepis. Human disturbance of the landscape is evident in the pollen spectra after ca. 3100 BP with the appearance of weed species. (C) 2003 Elsevier Science B.V. All rights reserved.