Pollen-based 17-kyr forest dynamics and climate change from the Western Cordillera of Colombia; no-analogue associations and temporarily lost biomes

Abstract

A 17kyr long pollen record from the unexplored Western Cordillera of Colombia (Páramo de Frontino; 3460m elevation) shows vegetation change and inferred climate dynamics at ~125yr resolution. The cold and wet Lateglacial showed well-defined stadials and interstadials. At the transition to the Holocene the upper forest line (UFL) shifted within 200years 700–800m upslope reflecting a temperature increase of ~4.5°C. Dead wood in the forests may have caused frequent fires. Individual taxa show clear and discrete successive expansion events, such as Podocarpus around 15calka, Quercus, Melastomataceae, Myrsine, Weinmannia, and Hesperomeles around 11.5calka, and Alnus around 9calka showing the floristic composition of the montane forest changed during its upslope migration. After forest had reached around 9calka a quasi-stable altitudinal interval forest taxa continued to change proportions showing that upslope forest migration caused significant internal forest dynamics. Forest stability is not found suggesting that an equilibrium between forest composition and environmental variables was not reached. We hypothesize trees migrated faster upslope than the shrubs causing a temporarily loss of this shrub biome. During most of the Holocene the UFL varied between 3500 and 3700m indicating warmer temperatures than today. High upper limits of subandean forest suggest that the lowermost level of significant night frost was at higher elevations than today. Driest pulses were registered ~9170 and ~8200calka since 620calka deforestation of Quercus, Podocarpus and Weinmannia in particular shows anthropogenic impact. Comparisons with other Andean climate records show a climatic asymmetry mainly related to migrations of the ITCZ. An implication of the present benchmark records of vegetation and climate variability and modeling is that new records should be analyzed at better than century resolution.