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

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 CO2 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 CO2 as a forcer of vegetation change; we run the model with concentrations of atmospheric CO2 ([CO2]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 [CO2]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 [CO2]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 [CO2]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 [CO2]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.