Montane forest evolution during the last 650 000 yr in Colombia: a multivariate approach based on pollen record Funza-I

Abstract

The core interval of 0–140 m of the 357-m-long pollen record from site Funza-I was analysed using multivariate analysis. This long continental record is from the high plain of Bogota, located at 2550 m altitude in the Eastern Cordillera of Colombia. Time control is based on a visual match with core Funza-II from the same location, which includes absolute fission-track ages, and a match with the δ18O record of ODP Site 677. We reassessed the time-frame of Funza-I compared with previous papers, and conclude that the period of ca. 650–25 kyr BP is represented. In this study 73 fossil taxa, present in > 4% of the 409 pollen assemblages, were analysed using the divisional classification program TWINSPAN. We recognised 10 cluster types that form three main cluster zones: W (warm), CW (cool) and C (cold). Pollen zones based on previous visual inspection were compared with new cluster types, which were graphed as a bar code along the pollen diagram. The use of two pollen sums (standard pollen sum, and a zonal pollen sum) appeared useful for identifying local effects on the forest composition. Modern pollen rain data for the study area were summarised. We used the concept of indicator taxa that behave as differential taxa to reconstruct climatic change. During the period of 650–330 kyr BP, Alnus, Hedyosmum, Weinmannia, Melastomataceae, Myrica and Podocarpus were the most important taxa of the Andean forest. The new time-frame indicates that the first scattered presence of Quercus started 478 kyr BP (102 m core depth), the first continuous presence was from 423 kyr BP (92 m), and the presence of zonal Quercus forest occurred from 330 kyr BP (72 m). During the period of 330–135 kyr BP, zonal Quercus and Weinmannia forest developed, replacing partly Podocarpus-dominated forest in the uppermost Andean forest belt. As a consequence, during the last 135 kyr BP, a high representation of Quercus on the high plain of Bogota no longer coincides with warm climatic conditions, but now occurs during cool to cold conditions. The pollen record was correlated with the δ18O record: temperature drop during Marine Oxygen Isotope Stage 4 and the very first part of Marine Oxygen Oxygen Stage 2 is calculated as a minimum of 6.6° to 7.8°C (excluding a potential effect of low glacial pCO2). The inferred maximum amplitude of the upper forest line during the last 650 kyr was from ca. 1900 to 3400 m (cf. 3200 m at the present-day), corresponding to a range of ca. +1.2°C to −7.8°C compared with today. Copyright © 2000 John Wiley & Sons, Ltd.