Palaeoenvironmental Changes during the Last 20,000 Years in the Humid Tropics : A Comparative Study by Means of Database and Palaeoenvironmental Map Compilation

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State of arts and future problems of palaeoenvironments research in the world humid tropics being elucidated by this project can be summarized as follows :1) The sites, where high-resolution pollen spectra with radiocarbon age controls from the LGM,are only 2-3 for every three humid tropical areas, i.e. Africa, Amazon and Southeast Asia-Australia.2) Even during the LGM extreme arid period, in Southeast Asia forests persisted on windward slopes exposed to the monsoons, and in the Zaire basin as gallery forests with montane taxa over the low plateaux. No valid data are available from the Amazon for this question.3) Pollen spectra have suggested that form mid-Holocene onward the climates of tropical South America and tropical Africa showed completely opposite tendency. However, no concrete explanations are so far available.4) Pollen spectra have shown that both in the Amazon and the Guineo-Congolian rainforests, forest began to reestablished from 14-13 ka, but full forest development achieved at ca. 9.5 ka for both regions. This cannot be explained by delayd response of vegetation, and requires reassessment of climate conditions.5) The most spectacular hydrogeomorphic events occurrecd during 13-10 ka in response to the return of tropical convective storms. In the Amazon, in addition, meltwater flux from the Andean Highlands must have playd important role in generating catastrophic floodings and the Amazon cone.6) Anthropogenic forest degradation and induced erosion and sedimentation date back to 9-7 ka in Southeast Asia, and ca. 3 ka in Africa. The data for this question are lacking for Amazon basin.7) More data with high time-resolution and the elimination of the effects of crustal movements on environmental changes are crucial to better comparative studies.