Paleoenvironmental history of the Popayan area since 27 000 yr BP at Timbio, Southern Colombia

A pollen record from Timbio, located at an elevation of 1750 m on the high plain of Popayan (2 degrees 24'N, 76 degrees 36'W) is presented. This forms the basis for reconstructing the vegetation and climate history for the pe riods from 27 000 to 9200 radiocarbon years before the present (C-14 yr BP) and 2100 C-14 yr BP to sub-recent. The 5 m sediment core has time control based on seven AMS radiocarbon dates. Four pollen assemblage zones (TIM-1 t o TIM-4) are recognized. During the period of 27 200 to 26 000 C-14 yr BP, an Andean forest was near the site. The vegetation consisted of forest and open herb-rich vegetation, climatic conditions were moist and temperatures some 6 degrees C lower than compared to those of today. During the period o f 26000 to 16000 C-14 yr BP forest was less open. The observed succession f rom a Podocarpus-Weinmannia dominated forest to a Hedyosmum dominated fores t, and finally to a forest with Ilex, Myrica and ferns indicates a progress ive decrease of temperature during this period, with a maximum temperature depression of ca. 5-7.5 degrees C compared to present-day conditions. Durin g the period of 16000 to 9200 C-14 yr BP, temperature decrease is estimated at ca. 7.5 degrees C and the climate was the driest. During the period of 2100 to 600 C-14 yr BP, deforestation and crop cultivation point to signifi cant human influence, subsequently followed by a period of forest recovery that started before the arrival of the Spanish conquistadors. The estimated temperature depression at the Last Glacial Maximum (LGM, ca. 6.5 degrees C ) is between the estimated values at >2600 m altitude (ca. 8 degrees C) and those at sea-level (2.5-6 degrees C) and supports the observation that gla cial lapse rates were higher than in modern times. (C) 2000 Elsevier Scienc e B.V. All rights reserved.