Palaeoenvironmental changes during the last ca. 8590 calibrated yr (7800 radiocarbon yr) in the dry forest ecosystem of the Patı ´a Valley, Southern Colombian Andes: a multiproxy approach M.I. Ve ´lez a , J.C. Berrı ´o a,b , H. Hooghiemstra a, * , S. Metcalfe c , R. Marchant a a Institute for Biodiversity and Ecosystem Dynamics (IBED), Graduate School of Geo-ecological Studies (ICG), Palynology and Paleo/Actuo-ecology, Faculty of Science, Kruislaan 318, 1098 SM Amsterdam, The Netherlands b Instituto de Ciencias Naturales (ICN), Universidad Nacional de Colombia. A.A. 7495 Bogota ´, Colombia c School of Geography, University of Nottingham. University Park, Nottingham NG7 2RD, UK Received 7 August 2003; received in revised form 20 July 2004; accepted 12 November 2004 Abstract Two sediment cores were recovered from two swamps in the dry forest lowland ecosystem of the Patı ´a Valley (Colombia). The 500-cm long core El Patı ´a-1 was analysed using diatoms, pollen, lithostratigraphy, geochemistry, charcoal and radiocarbon dates. The 270-cm long core Patı ´a-2 was analysed using pollen, lithostratigraphy and radiocarbon dates. The environmental reconstruction includes the local development and history of the Patı ´a-1 swamp and the regional vegetation history of the two swamps. The environmental reconstruction shows a fluvial system in the area before 7830 14 C yr BP (ca. 8590 cal yr BP). After this date, the river gradually moved away leading to the formation of the swamp Patı ´a-1; open vegetation with patches of dry forest surrounded the swamp. Between 7670 and 6860 14 C yr BP (8350–7690 cal yr BP), the swamp become partially isolated from the river and was a permanent water body which was alkaline and mesotrophic. During this period, the surroundings were covered by dry forest. From 6860 to 5870 14 C yr BP (7690–6690 cal yr BP), the swamp was totally isolated from the river and suffered from frequent periods of desiccation and erosion. From 5870 to 3570 14 C yr BP (6690–3890 cal yr BP), the swamp turned into a marsh/terrestrial environment and in the surrounding area, the dry forest alternated with open vegetation; it is possible that there were human impacts on the environment during this period. Between 3570 and 1990 14 C yr BP (3890–2000 cal yr BP), unstable conditions prevailed. After 1990 14 C yr BP (2000 cal yr BP), swamp conditions of permanent water were re-established; open vegetation surrounded the swamp. Agriculture and human activities were present and have continued since then. The climatic reconstruction suggests an increase in humidity at ca. 7670 14 C yr BP (8350 cal yr BP) and a dry climate between 6860 and 5870 14 C yr BP (7690–6690 cal yr BP). D 2004 Elsevier B.V. All rights reserved. Keywords: Colombia; Patı ´a Valley; Dry forest biome; Diatoms; Charcoal analysis; Pollen analysis 0031-0182/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2004.11.006 * Corresponding author. Tel.: +31 20 5257857; fax: +31 20 5257632. E-mail address: hooghiemstra@science.uva.nl (H. Hooghiemstra). Palaeogeography, Palaeoclimatology, Palaeoecology 216 (2005) 279– 302 www.elsevier.com/locate/palaeo