Late Holocene history of savanna gallery forest from Carimagua area, Colombia

The pollen record of a 65 cm long core Laguna Carimagua-Bosque (4 degrees 04'N, 70 degrees 13'W) shows the late Holocene environmental history from a lake located within the gallery forest of the savannas of the Llanos Orientales of Colombia. Nine AMS radiocarbon dates of the organic deposits show that the core represents the period from ca. 1300 C-14 yr BP to the present. The lake evolved from an active drainage system. During the period from ca. 1300 to 875 C-14 yr BP (zone CMB-Ia), Mauritia-dominated swamp and gallery forest was present, dominated by Cecropia, and later also Acalypha and Alchornea, From 875 to 700 C-14 yr BP (zone CMB-Ib), the lake was completely surrounded by gallery forest. Mauritiella and Cecropia occurred around the lake. Cecropia pioneer forest reached its greatest abundance and became gradually replaced by a more species-rich gallery forest, including Acalypha, Alchornea, Euterpe/Geonoma, Moraceae/Urticaceae, Piperaceae, and Virola. From 700 to 125 C-14 yr BP (zone CMB-II), Cecropia lost its dominant role, and Mauritiella palms became more frequent. The main vegetation categories were swamp forest, gallery forest, understory elements, savanna shrubs and trees, and grass savanna. From 125 C-14 yr BP to recent (zone CMB-III), the plant diversity in the gallery forest became highest, Mauritiella became very abundant, and among the savanna elements, woody Didymopanax increased. Comparison of four pollen records from savanna sites shows that pollen of savanna vegetation is markedly underrepresented in lake sediments when the lake lies within the gallery forest. As most of the drainage system of a savanna is hidden by gallery forest, we also expect a significant underrepresentation of the savanna ecosystem in river-transported pollen assemblages. (C) 2000 Elsevier Science B.V. All rights reserved.