Palaeoecological records of environmental change and cultural development from the Liangzhu and Qujialing archaeological sites in the middle and lower reaches of the Yangtze River

The cultures of Liangzhu (5200–4300 BP), Qujialing (5100–4500 BP) and Shijiahe (4600–4000 BP) are representative of Chinese civilization in the middle and lower reaches of the Yangtze River. Nevertheless, limited data is available on the rise and fall of pre-historical cultures in relation to environment in the Yangtze region. In this study, pollen, phytolith and microfossil charcoal extracted from sedimentary profiles and cultural layers at the archaeological sites of Liangzhu and Qujialing were employed to clarify the relationship between vegetation-climate and human cultures in archaeological context during Late Holocene in the middle and lower Yangtze River. The results suggest that forest was widely distributed under a warm and humid climate before the appearance of the Liangzhu culture and Qujialing culture (more than 5200 BP) in the two sites. During the Liangzhu, Qujialing and Shijiahe periods, virgin forest was damaged and secondary pine forest was expanded due to intensified agriculture. Palaeoecological records show the widespread rice cultivation during these phases, which might have provided steady food supply and hence laid a solid basis for the onset of the Chinese civilization. The civilizations of Liangzhu, Qujialing and Shijiahe collapsed at about 4300 BP, 4500 BP and 4000 BP respectively. Mixed sub-tropical evergreen and deciduous broad-leaved forest was restored rapidly following the collapse of Liangzhu civilization, implying warm and humid climate remained predominant throughout the time in the Liangzhu region. By contrast, the forest was not restored after the collapse of the Shijahe civilization: instead grassland vegetation developed, which is attributable to the over-exploitation of early humans and the ensuing dry climate. The warmer and more humid climate in the Liangzhu region seemed to have led to more stable and complex forest ecosystems, which were effective on standing against human impact and climate change. Soil erosion due to deforestation was also more frequent in Qujialing than Liangzhu, which must have further limited forest regeneration. Since 3700 BP, the climate became dry and forest declined in the two sites. During the Warring States period (2425–2171 BP), human disturbances, indicated by high percentages of Gramineae pollen and microfossil charcoal, were intensive, although the climate was not as warm and humid as mid-Holocene.