气候变化领域集成服务门户

Fossil pollen records from 31 sites with reliable chronologies and high-resolution data in the monsoonal region of China were synthesized to document Holocene vegetation and climate change and to understand the large-scale controls on these changes. The reconstruction of moisture histories was based on a four-class ordinal wetness index at 200-year time slices at individual sites. The vegetation experienced diverse changes over the Holocene in different regions: (1) between tropical seasonal rain forest and more open forest in tropical seasonal rain forest region; (2) from mixed evergreen and deciduous broadleaved forest to more deciduous or Pinus-dominated forest in subtropical region; (3) from mixed evergreen and deciduous broadleaved forest to deciduous forest in temperate deciduous forest region; (4) from deciduous broadleaved forest to conifer-deciduous forest in conifer-deciduous mixed forest region; (5) from steppe forest to steppe in temperate steppe region; and (6) from steppe forest/meadow to meadow/steppe in highland meadow/steppe region. Despite various vegetation sequences in different regions, our synthesis results show that a humid climate generally characterized the early and middle Holocene, and a drier climate prevailed during the late Holocene, with an abrupt shift at ca. 4.5 ka (I ka = 1000 cal yr BP). Abrupt palynological changes based on a squared-chord distance of pollen assemblages occurred at 11-10, 6-5 and 2-1 ka from most sites. The synthesized pattern of moisture change is similar to the ones inferred from other independent climate proxies; however, gradual vegetation changes in the early Holocene lagged about 1000 yr behind the summer monsoon maximum as indicated by speleothem isotope records from Dongge and Sanbao caves. Human activities likely affected vegetation change greatly during the late Holocene, but the magnitude and precise timing are less clear and require further investigation. (C) 2009 Elsevier B.V. All rights reserved.