Yoshinori Yasuda

Reconstruction of an 8,000-year Environmental History on Pollen Records from Lake Buyan, Central Bali

Open image in new window New evidence from Lake Buyan, a 65-m-deep caldera lake in central Bali, presents an 8,000-year record of vegetation and climate change through palynological and physio-geochemical analyses. The distinct sediment phases associated with relative vegetation fluctuations and change of physio-geochemical index suggest that Bali might have experienced cycles of wet and dry climate change over 8,000 years. Vegetation composed of marshland/gap-colonizers, being coeval with the intensive process of erosion as indicated by an increased input of minerogenic material from the catchment, characterizes the periods when homogeneous lake mud sediments are formed, indicating relatively higher rainfall at period of 8.0–6.6 ka BP, 5.1–3.6 ka BP and 2.8 ka BP to present. At the time when laminated lake sediments commence, e.g., 6.6–5.1 ka BP and 3.6–2.8 ka BP, vegetation of a rather dry and fire-resistant character dominates, in concomitant with lower input of minerogenic material and suggests drier episodes. Regional comparison indicates that human-induced vegetation destruction is insignificant in Bali, except that cultivation activities might have been manifested in the recent 3,000 years, and the climatic variability observed from this core was probably El Nino Southern Oscillation (ENSO)-related.

Climate Deterioration and Angkor’s Demise

Open image in new window Reconstruction of the paleoclimate based on analyses of annually laminated sediments in Japan and moat sediments from Angkor Thom in Cambodia indicates that there had been a period of drastic cooling during AD 1430–1500 accompanied by a weakening of monsoon activity. The annual mean temperatures show that—compared to the peak of medieval warm epoch around AD 1150—the mean temperature dropped by nearly 5°C in AD 1430. The climatic cooling brought about the weakening of the summer monsoon, which in turn would have resulted in the delayed arrival of the wet season. This might have had a catastrophic impact on rice cultivation in Cambodia leading to the decline of the Khmer Civilization.

Phum Snay and Its Significance in World History

Open image in new window Climate deterioration events that started around 4200 and 3200 cal. yr. BP influenced the decline of old world-order civilizations such as Mesopotamia, Egypt, Indus Valley, and Yangtze River. These events triggered large-scale ethnic migrations, which completely reconfigured the world map and thrust the world into a new era. The buds of new world order civilizations started to form, such as the empire of the Han people in China, the Roman Empire in the Mediterranean, and the Preclassic Mayan Civilization in the Central America. During the same period, in the peripheral regions of the Han Dynasty, the Yayoi culture emerged in Japan, the Dian Queendom rose in Yunnan Province, and complex societies were formed along the Mekong in Cambodia. These were rice-cultivating piscatory cultures and distinct from the wheat/barley/millet-cultivating pastoral cultures of the Han and Roman people. The climate abruptly began to ameliorate from 250 BC to 240 AD, when these new world-order civilizations began to flourish. Phum Snay is one of the representative prosperous cities of the new world-ordered civilizations that developed in the peripheral regions of the Han Dynasty, such as Dian Queendom in southern China and Yayoi in Japan.

Discovery of the Yangtze River Civilization in China

Open image in new window All of the birthplaces of ancient major civilizations in Eurasia, i.e., Mesopotamian, Egyptian, Indus Valley, and Yellow River, belonged to dry to semi-arid climates having annual rainfall of 500 mm or less, and were inhabited by people who mainly sustained themselves by cultivating wheat/barley and millet and by pastoral farming. On the other hand, people living in the wet climate and forested monsoon Asia, who sustained themselves by cultivating rice and fishing, developed a civilization that predated these ancient four great civilizations. This chapter shows the existence of an ancient civilization in the wet and forested monsoon Asia, the Yangtze River Civilization, mainly based on the excavation of the Chengtoushan site in Hunan Province, China.