Pollen-based biome reconstructions for the past 450 000 yr from the Funza-2 core, Colombia: comparisons with model-based vegetation reconstructions

Abstract

The 586-m Funza-2 sequence from the high plain of Bogotá, Colombia has provided one of the longest pollen-based vegetation reconstructions in the world. Affinity scores to seven biomes are compared to the record of CO 2 fluctuation from the Vostok ice core for the period spanning from approximately 25 000 to 450 000 yr before present (BP). Results are compared to output from the BIOME-3 vegetation model run under different environmental scenarios at regional and local scales. The model is run with temperature and precipitation reductions, relative to the present values, of up to −10°C and −700 mm yr −1 respectively. For this particular investigation we are interested in the role of CO 2 as a forcer of vegetation change; we run the model with concentrations of atmospheric CO 2 ([CO 2] atm.) within the range of 170 to 340 ppmV. During glacial periods, the cool grass/shrubland biome is highly dominant, less so during interglacial periods when the cool evergreen and cool mixed forest biomes become co-dominant. In addition to this climate-driven altitudinal oscillation of the vegetation, there is also a signal that indicates longer term evolution of the vegetation. The cool grass/shrubland and cool evergreen and cool mixed forest biomes become co-dominant for the first time over the 450 000-yr record at approximately 170 000 yr BP, become completely anti-phase (during a period of extreme low [CO 2] atm.) and then become co-dominant from approximately 120 000 yr BP until the core top, just prior to the last glacial maximum. The model results for the Funza area indicate that changes in [CO 2] atm., temperature and precipitation are inter-linked by the vegetation response. A shift of 5.5°C is required to lower the cool grass/shrubland biome to altitudes about the Funza catchment where the Andean forest biome dominant. At low [CO 2] atm. concentrations, particularly below 180 ppmV, the composition of the high latitudinal tropical vegetation about the Funza catchment changed. It is suggested that this low [CO 2] atm., combined with a period when the climate was characterised by extreme cooling and drying, caused a readjustment of the tropical high altitudinal vegetation zonation and the formation of plant communities that are presently recorded.