Quantitative reassessment of Holocene vegetation change on the upper Tibetan Plateau
Fossil pollen records on the Tibetan Plateau have been widely used to infer the past climate changes, which however, demands better understandings in the vegetation changes. Previous studies based on fossil pollen data have reported significant changes in vegetation on the alpine Tibetan Plateau during the Holocene. However, since the relative proportions of fossil pollen taxa are largely influenced by individual pollen productivities and the dispersal characteristics, such inferences on vegetation have the potential to be considerably biased. We therefore reexamined the modern pollenvegetation relationships for four common pollen species on the Tibetan Plateau, using Extended R- value (ERV) models. Using Poaceae as the reference taxa, high PPEs were deduced for Artemisia and Chenopodiaceae, and Low PPE for the Cyperaceae. Applying these PPEs to four fossil pollen sequences since the Late Glacial, the plant abundances on the central and north-eastern Tibetan Plateau were quantified using the “REVEALS” model. The proportions of Artemisia and Chenopodiaceae were greatly reduced compared to their original pollen percentages in the reconstructed vegetation, while Cyperaceae showed a relative increase in the vegetation reconstruction. The reconstructed vegetation assemblages always yielded smaller compositional species turnovers than suggested by the pollen spectra, as revealed by Detrended Canonical Correspondence Analyses (DCCA) of the Holocene sections, which indicates that the strength of the previously reported vegetation changes may therefore have been overestimated (Wang, Y.B. and Herzschuh, U., 2011)