Pollen and non-pollen palynomorph analyses of Upper Holocene sediments from Dianshan, Yangtze coastal lowlands, China: Hydrology, vegetation history and human activity

Abstract

The coastal deltaic plain of the Yangtze River between Taihu (Lake Tai) and Shanghai in eastern China has been the scene of human settlement and agriculture since the early Neolithic, becoming increasingly intensive in the Upper Holocene when delta accretion and the establishment of a stable hydrological regime of freshwater lakes and wetlands allowed the development of extensive agriculture and complex society in late prehistoric and dynastic times. During this period the area was significantly affected by changes in sea level, climate and vegetation, resulting in a dynamic and complex environmental history, however little research has concentrated on environmental change and human impacts during the last few millennia. This study focuses on this late period, presenting the results of integrated sedimentary, microfossil and radiocarbon analyses from a core near the eastern margin of Lake Dianshan, to the east of Taihu. After the withdrawal of intertidal conditions and the conversion to freshwater lake at the core site about 2600 cal. yr BP, pollen and algal spore data show that increased sedimentation gradually reduced freshwater depth until a surface peat formed ca. 1500 cal. yr BP. This also dates the start of a switch in woodlands from sub-tropical and warm temperate trees to a mainly cool temperate and coniferous tree flora, under climatic cooling and human impact. After this time water depths at the site increased greatly, partly due to climate change and flooding, but also because of the establishment of deepwater ‘paddy’ agriculture. Microcharcoal and pollen data show that a major episode of human impact using fire, with deforestation and rice cultivation, occurred between ca. 1500 and 1200 cal. yr BP. These dates suggest it is one of the latest examples of ‘flooded-field’ ‘paddy’ cultivation before more intensive agricultural techniques were adopted in the area after ca. 800 cal. yr BP.