Environmental history of the Colombian savannas of the Llanos Orientales since the Last Glacial Maximum from lake records El Pinal and Carimagua

Late Quaternary environments have been studied by pollen analysis of lake sediments from the savannas of the Colombian Llanos Orientales at 180 m elevation. The pollen record form Laguna El Pinal (4 degrees 08'N, 70 degrees 23'W), dated by 6 AMS radiocarbon dates, starts at 18,290 C-14 yr B.P. The record from Laguna Carimagua (4 degrees 04'N, 70 degrees 14'W), also dated by 6 AMS dates, starts at 8270 C-14 yr B.P. Both records show a landscape dominated by grassland savanna with only few woody savanna taxa, such as Curatella and Byrsonima, frequent fires, and little occurrence of forest and/or gallery forest along the rivers. The savanna ecosystem at the studied sites was relatively stable during the last 18,000 yrs, but minor changes in floral composition, and in the proportion of savanna/forest, have been recorded. Very little gallery forest and the non permanent lake conditions of Laguna El Pinal reflect the driest period, interpreted to reflect low rainfall rates and long dry seasons during the Last Glacial Maximum until 10,690 C-14 yr B.P. During the Late Glacial, Laguna El Pinal was a permanent shallow lake, and changed into a lake with higher water levels during the Holocene, indicating wetter conditions. Expansion of regional gallery forest also started at around 10,690 C-14 yr B.P. Little vegetational change observed in Laguna Carimagua at 5570 C-14 yr B.P., in combination with a simultaneous decrease of savanna observed in previously studied lakes, suggest a change to regional wetter conditions. Thus, the Holocene before 5500 C-14 yr B.P. was somewhat drier than the following period until about 3850 C-14 yr B.P. In both records, Late Holocene lake deposits are incomplete. Shore vegetation of Laguna Carimagua always included a minor contribution of the palms Mauritia and Mauritiella. The marked increase of palms during the last c. 3800 yrs points to increased human impact on the vegetation under the wettest Holocene climate regime.