Late Quaternary palaeoecology and palaeoclimatology from pollen records of the savannas of the Llanos Orientales in Colombia
Abstract Pollen analysis of sediment cores from Laguna Angel (4°28′N, 70°34′W, 200 m elevation) and Laguna Sardinas (4°58′N, 69°28′W, 80 m a.s.l.) in the savannas of the Llanos Orientales of Colombia are presented. The pollen record of Laguna Angel includes 7 radiocarbon dates and shows the Holocene vegetation and climatic history since 10,030 yr B.P. The record of Laguna Sardinas includes 7 radiocarbon dates and shows the late Glacial and Holocene history since 11,570 yr B.P. Both pollen records show that the present-day savanna vegetation, dominated by grassland (Poaceae) with only few woody savanna taxa (e.g. Curatella, Bryrsonima ), was present since the late Glacial, indicating dry climatic conditions with a marked dry season. Shrubs and trees of forest and/or gallery forest, e.g. Mauritia, Mauritiella , Moraceae/Urticaceae, Melastomataceae, Alchornea , and Myrtaceae are well represented during the recorded period. The proportions between forest and savanna were subject to change in the past, but also the composition of the forest and savanna ecosystems changed. Laguna Sardinas shows a greater abundance during the late Glacial/Holocene transition than today for Alchornea , especially from 10,680 to 10,070 yr B.P. For this interval, synchronous to the El Abra stadial (Younger Dryas equivalent) in Colombia, more humid climatic conditions have been inferred, which are primarily the result of higher moisture levels under colder conditions. During the early and middle Holocene, from 9730 to 5260 yr B.P. in Laguna Angel, and from 9390 to 6390 yr B.P. in Laguna Sardinas, the maximum expansion of grassland occurred, indicating very dry climatic conditions. The following period, from 5260 to 3890 yr B.P. in Laguna Angel, and from 6390 to 3680 yr B.P. in Laguna Sardinas, shows a decrease of savanna herbs and an increase of forest and gallery forests, reflecting a wetter period, probably with a shorter annual dry season. In both lake records, the period after ca. 3500 yr B.P. is incomplete, but is characterized by a high representation of the palm genera Mauritiella in Laguna Angel, and Mauritia in Laguna Sardinas. This marked change has been interpreted as evidence of strong a anthropogenic influence on the vegetation, but also wetter climatic conditions than during the late Glacial and early and middle Holocene periods.