Tropical Forests Under the Climates of the Last 30,000 Years

Vegetational history can help us to predict future environments by providing data for testing AGCMs, for indicating the vegetational response to rapid warming and changing CO2 concentrations, and for mathematical modelling of vegetation. Most of the data are palynological, and there are well over 100 pollen diagrams from tropical regions. Maps are presented showing summarized pollen diagrams from the lowlands of South-East Asia and the West Pacific, Tropical Latin America and Tropical Africa. In all these regions there is some evidence suggesting that at the LGM lowland forests were somewhat restricted in area and included montane elements. This is consistent with cooler and drier climate at the LGM. From the montane and lowland areas of these three regions, the pollen evidence is summarized in altitudinal diagrams. These suggest considerable depression of altitudinal zones at the LGM, suggesting temperatures c. 5–10°C cooler than now. These results conflict with earlier oxygen isotope data from marine foraminifera, but do not conflict with more recent oxygen isotope measurements from tropical corals. It is also suggested that altitudinal movements may be partly controlled by CO2 concentration and ultraviolet light.