Late-glacial and Holocene history of the dry forest area in the south Colombian Cauca Valley

Two sedimentary cores with pollen, charcoal and radiocarbon data are presented. These records document the Late-glacial and Holocene dry forest vegetation, fire and environmental history of the southern Cauca Valley in Colombia (1020 m). Core Quilichao-1 (640 cm; 3degrees6'N, 76degrees31W) represents the periods of 13 150-7720 C-14 yr BP and, following a hiatus, from 2880 14C yr BP to modern. Core La Teta-2 (250 cm; 3degrees5'N, 76degrees32W) provides a continuous record from 8700 C-14 yr BP to modern. Around 13 150 C-14 yr BP core Quilichao-1 shows an active Late-glacial drainage system and presence of dry forest. From 11 465 to 10520 C-14 yr BP dry forest consists mainly of Crotalaria, Moraceae/Urticaceae, Melastomataceae/Combretaceae, Piper and low stature trees, such as Acalypha, Alchornea, Cecropia and Celtis. At higher elevation Andean forest comprising Alnus, Hedyosmum, Quercus and Myrica was common. After 10520 C-14 yr BP the floral composition of dry forest changed, with extensive open grass vegetation indicative of dry climatic conditions. This event may coincide with the change to cool and dry conditions in the second part of the El Abra stadial, an equivalent to the Younger Dryas. From 8850 C-14 yr BP the record from La Teta indicates dry climatic conditions relative to the present, these prevailing up to 2880 C-14 yr BP at Quilichao and to 2720 C-14 yr BP at La Teta. Severe dryness reached maxima at 7500 C-14 yr BP and 4300 C-14 yr BP, when dry forest reached maximum expansion. Dry forest was gradually replaced by grassy vegetation, reaching maximum expansion around 2300 C-14 yr BP. After 2300 C-14 yr BP grassy vegetation remains abundant. Presence of crop taxa (a.o. Zea mays), disturbance indicators (Cecropia) and an increase in charcoal point to the presence of pre-Columbian people since 2300 C-14 yr BP. After 950 C-14 yr BP, expansion of secondary forest taxa may indicate depopulation and abandonment of previously cultivated land. After 400 C-14 yr BP, possibly related to the Spanish conquest, secondary forest expanded and charcoal concentrations increased, possibly indicating further reduction of cultivated land. During the past century, Heliotropium and Didymopanax became abundant in an increasingly degraded landscape. Copyright (C) 2002 John Wiley Sons, Ltd.