A SYNOPSIS OF CLIMATIC AND VEGETATIONAL CHANGE IN SOUTHEAST ASIA LAWRENCE R. HEANEY Department of Zoology, Field Musem of Natural History, Roosevelt Road at Lake Shore Drive, Chicago, IL 60605, U.S.A. Abstract. Tropical rain forest in Southeast Asia has developed within an extensive archipelago during the past 65 million years or more. During the Miocene (begin- ning 25 million years BP), rain forest extended much further north (to southern China and Japan); since that time it has contracted. During the Pleistocene (begin- ning 2.0 million years BP), development of continental glaciers at high latitudes was associated in Southeast Asia with lowered sea level, cooler temperatures, and modified rainfall patterns. Fossil pollen records demonstrate that Southeast Asian vegetation during the last glacial maximum (ca. 18 000 BP) differed substantially from that of today, with an increase in the extent of montane vegetation and savan- nah and a decline in rain forest. These data show that the distribution and extent of rain forest in Southeast Asia has historically been quite sensitive to climatic change. Introduction About one-fourth of the world's existing tropical rain forest occurs in Indo-Austral- ia, and taken as a whole these forests are second in area only to those of Latin America. But unlike the rain forest of Latin America and Africa that occurred naturally as vast expanses of nearly continuous forest, the forest of Indo-Australia is scattered on two continents and thousands of islands. In Indo-Australia, the area from Sri Lanka and India to New Guinea and northern Australia, this geographic discontinuity is strongly associated with exceptionally high localized biological diversity; the mammal fauna of the Philippines, for example, includes over 100 spe- cies found nowhere else (Heaney, in press). In South America and Africa, temporal changes in the extent of rain forest have been determined primarily by variation in temperature and rainfall. In Indo- Australia, these factors have played crucial roles as well, but another variable, sea level, has been equally, and at times more, important. Current sea level is near to the maximum level that has existed at any time during the past several million years, but geologically recent glacial episodes often have resulted in sea level more than 100 m below the present level. Such changes have had relatively little effect on the land area of Africa or South America, but have drastically altered the area and con- figuration of Indo-Australia. These changes have directly influenced rainfall, adding to the complexity of the vegetational history of the region. The complexity of Indo-Australia makes it impossible to cover all parts of the region adequately in a brief review; this paper therefore focuses on Southeast Asia, Climatic Change 19: 53-61, 1991. 9 1991 KluwerAcademic Publishers. Printed in the Netherlands.