VEGETATION CHANGE IN SIBERIA AND THE NORTHEAST OF RUSSIA DURING THE CENOZOIC COOLING: A STUDY BASED ON DIVERSITY OF PLANT FUNCTIONAL TYPES

摘要

Cenozoic vegetation change in Western Siberia and northeastern Russia is quantified based on the analysis of diversity of plant functional types (PFTs). Carpofloras (148 total) compiled from published sources are assigned to a total of nine time slices spanning the period from the middle Eocene to the late Pliocene. Comparisons among four defined key regions allow study of spatial diversity gradients and their evolution. Our novel PFT classification scheme, designed for use in biome modeling, comprises 26 herbaceous to arboreal PFTs based on physiognomic characters and bioclimatic tolerances of plants, completed by an aquatic PFT. Using multivariate statistics, localities with similar PFT spectra are grouped and interpreted in terms of biomes. The results are visualized on paleovegetation maps and in PFT diversity records documenting vegetation evolution by key region. In northeastern Russia, mixed and conifer forest biomes existed during the Neogene. Diversity spectra indicate that even in the late Neogene, warm and humid conditions prevailed in this region, probably related to coeval intensification of the East Asian monsoon system. In Western Siberia, mesophytic forests with higher proportions of broadleaved evergreens dominated during the earlier Paleogene. Subsequent vegetation change is mainly expressed by a steadily increasing diversity of herbaceous PFTs. In the southern part of Western Siberia, distinct opening of the vegetation occurred in the late Miocene, connected to drying. The coeval declining trend of thermophilous PFTs in the north coincides with intensified cooling of the high latitudes.