Late-Holocene natural and anthropogenic vegetation changes in the Dongbei Pingyuan (Manchurian Plain), northeastern China

摘要

Two peat profiles from the Manchurian Plain in northeastern China, with chronology based on 20 AMS measurements, provide new evidence for natural and anthropogenic environmental changes that occurred in the region during late Holocene. The onset of continuous organic accumulation interpreted as climatically induced shift in hydrological regime was dated at the Muchang site to 4200 (uncal.) BP, and at the Dahuofang site to at least 3560 BP. The start of peat growth, documented in the Muchang profile, was preceded by temporal intensification of fluvial processes around 4400/4300 BP. The evidence of hydrological changes in the Manchurian Plain correlates with the spread of Korean pine in the nearby Changbai mts. area in 4300-4000 BP, and can be associated with the initial stages of a trend towards present-day climatic conditions in the region. Late Holocene pollen sequences from Muchang and Dahuofang revealed the presence of oak and pine forests with the other minor deciduous constituents as Ulmus, Tilia, Carpinus, Acer and Fraxinus. Local distribution of oak was confirmed by plant macrofossil remains (leaf fragments) ascribed to Quercus x hopeiensis. The vegetation cover formed sparse woodland or mosaic of forests and steppe communities with Artemisia, Gramineae and Chenopodiaceae. Fossil pollen data clearly indicates that the spread of grasslands in the western part of Manchurian Plain occurred as a result of human impact. Extensive deforestation accompanied by agricultural practices (buckwheat cultivation) has been dated to 900-1100 cal yr AD and were correlated with development of the state of Liao dynasty (907-1125 AD). Evidence of earlier human involvement in forest destruction has been dated to around 900 cal yr BC. With each progressing anthropogenic deforestations phase, there was increased circulation of eolian dust resulting from landscape opening and soil erosion.