Holocene wildfires related to climate and land-use change over the Weihe River Basin, China

Abstract

Charcoal particles preserved in the loess-palaeosol profiles provide records of wildfires during the Holocene. Total organic carbon, magnetic susceptibility and charcoal analysis and OSL dating were carried out in the Holocene loess-palaeosol profiles at two sites in the Weihe River basin. The analytical results show that natural wildfires occurred frequently during the last glaciation when climate was dominated by northwest continental monsoon and steppe vegetation expanded southerly to the Weihe River basin. Wildfire occurrence decreased during climatic amelioration in the early Holocene. During the Holocene Climatic Optimum between 8500 B.P. and 3100 B.P., natural wildfire occurrence was reduced greatly. Pedogenic alteration to the accumulated dust was intensified because of the humid-warm climate brought on by southeast maritime monsoon. Localized fire events in connection with human activities of the Neolithic occurred in several episodes over the region. During the late Holocene when climate become drier, wildfire occurrence over the upland hills shows a pattern different from that in the Guanzhong Basin. Over the upland hills in the north, charcoal concentrations show a decreasing trend in the recent loess and topsoil. It indicates infrequent biomass burning during the last 3100 years. This is attributable to nomadic occupation of the loess hills during the Bronze Age and the development of a land-use pattern of livestock farming in most part of the history. Over the loess tableland in the Guanzhong Basin in the south, abruptly increased charcoal concentrations in the recent loess and topsoil show very high level of biomass burning. This is attributable to the increasingly intensified land reclamation for cereal cultivation from the Bronze Age. This study provides new insights into wildfires over the semi-arid and sub-humid regions in connection with climate and land-use change.