Quantitative relationships between modern pollen rain and climate in the Tibetan Plateau

Quantitative relationships between modern pollen rain and climate are poorly studied in China, partly due to the extensive human impact on the modern vegetation. A dataset consisting of 227 modern pollen samples from forests, shrublands, meadows, steppes, and deserts in the Tibetan Plateau, the least anthropologically-disturbed region in China, provides a unique opportunity to study the quantitative relationships between modern pollen rain and climate. Pollen percentage data were calculated on a sum of 20 pollen taxa. Climatic data for each site, including mean annual precipitation (MAP), mean annual temperature (MAT), July temperature (T_july), and January temperature (T_jan), were derived from 214 meteorological stations in the Tibetan Plateau and adjacent areas using natural neighbor interpolation and linear interpolation methods. Canonical correspondence analysis (CCA) was used to reveal the climatic parameters that best reflect the main patterns of variation in the modern pollen rain, and to detect anomalous observations. Results of CCA indicate that MAP and T_july are two climatic parameters controlling the variation of modern pollen rain in the Tibetan Plateau. Pollen-climate transfer functions for MAP and T_july were then developed using the inverse linear regression and weighted-averaging partial least squares regression models. The functions derived from these two models are statistically significant at the 0.0000 level. A case study, in which these functions were applied to a fossil pollen record from an alpine lake in the eastern Tibetan Plateau, was conducted to show the feasibility of these functions in paleoclimate reconstruction. The results demonstrated the applicability of these pollen-climate transfer functions to fossil pollen data.