Amazonian ecosystems and atmospheric change since the last glacial maximum

This chapter reviews previously published palaeovegetation and independent palaeoclimatic datasets to determine the responses of Amazonian ecosystems to changes in temperature, precipitation, and atmospheric CO₂ concentrations that occurred since the last glacial maximum (LGM), about 21,000 years ago, and it uses this long-term perspective to predict the likely vegetation responses to future climate change. Amazonia remained predominantly forested at the LGM, although savannas expanded at the margins of the basin. The combination of reduced temperatures, precipitation, and atmospheric CO₂ con...

This chapter reviews previously published palaeovegetation and independent palaeoclimatic datasets to determine the responses of Amazonian ecosystems to changes in temperature, precipitation, and atmospheric CO₂ concentrations that occurred since the last glacial maximum (LGM), about 21,000 years ago, and it uses this long-term perspective to predict the likely vegetation responses to future climate change. Amazonia remained predominantly forested at the LGM, although savannas expanded at the margins of the basin. The combination of reduced temperatures, precipitation, and atmospheric CO₂ concentrations resulted in forests structurally and floristically quite different from those of today. Evergreen rainforest distribution increased during the glacial-Holocene transition due to ameliorating climatic and CO₂ conditions. However, reduced precipitation in the early-mid Holocene (about 8000-3600 years ago) period caused widespread, frequent fires in seasonal southern Amazonia, with increased abundance of drought-tolerant dry forest taxa and savanna in ecotonal areas. Rainforests expanded once again in the late Holocene period as a result of increased precipitation. The plant communities that existed during the early-mid Holocene period may constitute the closest analogues to the kinds of vegetation responses expected from similar increases in temperature and aridity posited for the 21st century.