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The Nihewan Formation is an important early Quaternary sedimentary formation in North China. We conducted pollen analyses of 183 samples and 1611 modern surface samples to characterize the processes of vegetation succession and climate change during the Pliocene-Pleistocene transition (2.89–2.34 Ma) in the Nihewan Basin. The results show that pollen assemblages are dominated by arboreal pollen, indicating that the vegetation in the study area was forest dominated and that the climate was more humid than today, however, the temperature varied substantially. The most substantial vegetation and climate changes occurred at ∼2.8 Ma, when the pollen representation of warm and humid tolerant taxa such as evergreen Quercus and Carya disappeared, and also broadleaved deciduous types such as Ulmus, deciduous Quercus and Betula decreased obviously, on the contrary, the pollen representation of cold and drought tolerant taxa increased substantially: e.g. Picea (from generally less than 20% to more than 30%) and Chenopodiaceae (from generally less than 10% to more than 20%). The quantitative reconstructed results indicating that Tann decreased by about 2–3 °C and Pann decreased by ∼150 mm compared to before 2.8 Ma, with a maximum decrease of ∼9 °C for Tann and ∼450 mm for Pann. Another important vegetation and climate changes occurred at ∼2.6 Ma, which was the coldest and driest of the studied interval, when the vegetation was substantially simplified with spruce (generally above 80%) as the dominated types.
•During the Pliocene-Pleistocene transition (2.89–2.34 Ma), the vegetation in the Nihewan Basin was dominated by forest.•The most pronounced change from warm-humid to cold-dry environment occurred at ∼2.8 Ma.•Three warm periods and three cold periods can be defined.•The duration of the cold periods were longer than that of the warm periods.