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Pollen analysis was conducted for loess deposits from three sites in the western Chinese Loess Plateau, i.e. the loess area west of the Liupan Mountains. Results show that during the Last Glacial Maximum (LGM), in-situ vegetation was dominated by Artemisia and some drought-tolerant species such as Echinops-type, Chenopodiaceae, Nitraria, and Ephedra, while coniferous forest (mainly Picea) flourished in nearby river valleys. During the Holocene Optimum, Picea almost disappeared, and Echinops-type, Chenopodiaceae, Nitraria and Ephedra decreased; vegetation was characterized by Artemisia, Taraxacum-type, Polygonaceae and Leguminosae, implying the climate was warmer and wetter than during the LGM. During the late Holocene, Chenopodiaceae, indicator of human-managed habitats, increased in the study area, indicating enhanced human activity.

The climate was warmer and more humid in the loess areas east of the Liupan Mountains than in the west during both the LGM and Holocene Optimum. Likewise, a significant difference in specific plant types was observed between the east and west since the LGM. During the LGM, Pinus and some broadleaf trees emerged, but no Picea forest grew, while in the west, vegetation was characterized by desert shrub and desert steppe in situ, and by dark coniferous forests (mainly Picea) in nearby river valleys. During the Holocene Optimum, treeline advanced upward as a result of increased temperature. Picea thus withdrew from the western loess areas. Therefore, temperature is the major factor controlling the growth of Picea in the Chinese Loess Plateau. (C) 2014 Elsevier Ltd and INQUA. All rights reserved.