Holocene history of desertification along the woodland-steppe border in northern China

The woodland-steppe ecotone of the southeastern Inner Mongolian Plateau in northern China is located at the northwestern limit of the Pacific monsoon influence, where the landscape may have been a sensitive recorder of past climatic changes. Physical, chemical, and biological analyses of AMS C-14-dated sediment sequences from two lakes of this region were used to reconstruct the Holocene vegetation and desertification history and distinguish four periods: (1) a cold and humid period from 10000 to 8000 C-14 yr B.P., (2) a warm and humid period from 8000 to 5900 C-14 yr B.P., (3) a warm and dry period from 5900 to 2900 C-14 yr B.P., and (4) a cool and dry period from 2900 C-14 yr B.P. to the present. The increased aridity during the middle Holocene was likely caused by increased winter temperatures and enhanced winter evaporation. The transition from a humid to an and climate after similar to5900 C-14 yr B.P. coincided with enhanced aeolian activity, and deciduous woodlands were replaced by pine woodlands and then by steppes in response to the climatic deterioration. These transitions led to the present desertification. The records suggest that a simple association of thermal and moisture conditions, such as warm/wet or cold/dry, may be misleading. (C) 2002 University of Washington.