CHARCOAL RECORDS OF HOLOCENE WILDFIRES AND ENVIRONMENTAL CHANGES IN THE WEIHE RIVER DRAINAGE

The Weihe River drainage is situated in semi-arid and sub-humid monsoon-sensitive areas in the north of China. Charcoal preserved in the loess-soil profile provided records of wildfire history and climatic changes during the late Holocene. Total organic carbon, magnetic susceptibility and charcoal analysis of two Holocene loess profiles in the study area have revealed the relationship between Holocene wildfire activity, human activity and climatic changes. The results show that the climate was arid and local wildfire occurred frequently during the late time of the last glacial period before 11 500 aBP when steppe vegetation expanded from the Inner Mongolian Plateau southerly over the Weihe River drainage. Conversely, wildfires were reduced during the early Holocene. During the Holocene climatic optimum between 8 500 and 3 100 aBP, natural wildfires were largely reduced. Pathogenic alteration to the accumulated dust processes was so active that forest-grassland formed under the humid-warm climate of the Holocene Megathermal. However, localized wildfires in connection with human activities frequently occurred in different patterns at the study sites. With the drier climate and more intensified historical land-use, human-set fires were more common than the natural fires. Very high levels of biomass burning and deteriorated land-use conditions caused a regional desertion by the arable farming communities and the invasion of nomads in the northern part of the Weihe River drainage during the last 3 100 years. After 1 500 aBP,the amount of charcoal sharply decreased and wildfire occurrence slowly disappeared, which may have resulted from totally cultivated land for farming and fully established agricultural landscape in the southern part of Weihe River drainage of the Loess Plateau; meanwhile, mixed agriculture of semi-cultivation and semi-animal husbandry was gradually developed in the northern part of the Weihe River drainage.