Late Quaternary pollen records from the middle Caqueta river basin in central Colombian Amazon

Three pollen records are presented from the Pantano de Monica region (0 deg rees 42'S, 72 degrees 04'W, 160 m elevation) on the lower terrace of Rio Ca clueta of the central Colombian Amazonas. Ten radiocarbon dates from three cores indicate that the deposits are of Holocene age, but the pollen data s uggest that the record may also contain the Late Glacial. The core Pantano de Monica I covers the time interval from 11,150 BP (extrapolated) to 4730 BP. During the Late Glacial and early Holocene this swamp was smaller in si ze and waters were more shallow than today, with abundant Mauritia palm tre es. This indicates that the lower terrace of the Caqueta River was better d rained than today, which might be related to changes in the drainage system and/or drier conditions during that time. Late Glacial and early Holocene vegetational changes in the rain forests surrounding the swamp Pantano de M onica indicate successional stages, probably related to changes in the drai nage system and/or climate changes. Presence of Podocarpus pollen grains up to 2.6% of the total sum (and influx of 78 grains cm(-2) yr(-1)) point to the regional presence of Podocarpus at the beginning of the Holocene. Evide nce of Podocarpus during glacial times in other pollen records from the Ama zon basin has been taken as indicative of cooling. Core Pantano de Monica 2 was taken in a small swamp (1000 m distance to Pantano de Monica 1) and st arts at 4000 BP when this location was well drained. Several changes in the composition of the rain forest are documented, such as increase in disturb ance (increase of Cecropia) followed by a quick recovery (increase of Psych otria). Protium and Caryocar tree taxa were frequent, suggesting that the l ower terrace area was well drained until 3080 BP, after which small swamps developed. Core Pantano de Monica 3 is from the wet forest in between the t wo swamps and represents the period since 3260 BP. Pollen data show a conti nuously increasing presence of palms, probably Euterpe, suggesting either a transition from well-drained to less drained conditions in the lower terra ce during the late Holocene, and/or a more intensive human impact of the ra in forest on the lower terraces of Rio Caqueta. The three records from the lower terrace of Rio Caqueta show different forest compositions in the past and indicate that the rain forest environments were not stable during Late Glacial and Holocene times. Comparison with other data from lowland record s of northwestern South America suggest that climate change is a major fact or for environmental change in central Colombian Amazon. (C) 1999 Elsevier Science B.V. All rights reserved.