Holocene fire and forest histories in relation to climate change and agriculture development in southeastern China

Four cores (GY1, LTY, SZY, GT-2) taken from lowland to mountain sites in southeastern subtropical China were studied. Charcoal and pollen analyses were conducted to examine the regional Holocene fire history and discuss its possible relationship with both climatic changes and anthropogenic activities. Our results show extremely low charcoal influxes between 9.5 and 3.5 cal ka BP, revealing low fire frequency. Meanwhile, high proportions of arboreal pollen demonstrated expansion of subtropical evergreen broadleaf forest. This phase is consistent with heavy precipitation during the early-mid Holocene. After 3.5 cal ka BP., the abrupt increases in fire frequency revealed by core GY1 and LTY were closely related to gradual drying towards the late Holocene, possibly due to the Asian Summer Monsoon weakening and activation of the El Niño Southern Oscillation. Our pollen records also reveal this drying trend after the mid-Holocene, demonstrating a regional retreat of subtropical evergreen forests and local development of Glyptostrobus-dominated wetland community around the LTY and GY1 sites. However, the intensified fires after 3.5 cal ka BP probably resulted mainly from increasing human activities during the Shang-Zhou Bronze age. Pollen results show severe damage of forest by fires, indicated by notable decrease of arboreal pollen and increase of Dicranopteris and herbs. After 2.0 ka, obvious growth of Poaceae, Dicranopteris and Pinus recorded in the GY1 and LTY cores demonstrate agriculture development in low-altitude plains and hills, coinciding with the first human population boom and big progress in agricultural technology during the Warring States to Western Han Dynasty period. Signs of profound human impacts and extensive agriculture in South China appeared after 1.0 cal ka BP, which is revealed by frequent local fires and intensified anthropogenic impact around the mountains sites (SZY and GT-2). Generally, our results reveal a gradual expansion of anthropogenic activities into elevated areas.