To reconstruct the distribution changes of tropical seasonal forests in the several regions in Thailand, from early Holocene to recently, analyses of fossil opal phytolith were carried out together with radiocarbon dating. Three paleovegetation types were identified from the composition of Shorea type and Bambusoideae phytolith assemblages and radiocarbon dates. A-type is distinguished by a standing of temperate deciduous dipterocarp forest on the flatland less than 100m above sea level of the northern Malay Peninsula (after ca. 9,300yrsBP). B-type is defined by increasing of temperate deciduous dipterocarp forest with Bambusoideae in the forest floor on inner hills, northeast Thailand (after ca. 5,000-4,500yrsBP). C-type is characterized by vegetational flora in mountainous areas more than 500m above sea level in northern Thailand (after ca. 1,000yrsBP). It was revealed that deciduous dipterocarp forest expanded from low latitudes to high, and from low land to highlands. It was suggested that paleovegetation was induced not only by environmental change, but also by human impact on ecosystems.
Recent developments of mass spectrometry enable us to conduct high-precision and high-resolution dating on samples to study paleoenvironmental conditions during the Quaternary. In particular, radiocarbon dating using small accelerator mass spectrometers is a highlight, and combinations with statistical analyses reveal detailed histories of the Earth’s surface environment. In this paper, I introduce our activities on these topics and discuss the importance of the approach.