Cenozoic vegetation gradients in the mid- and higher latitudes of Central Eurasia and climatic implications

Abstract

Cenozoic vegetation gradients in the mid- and higher latitudes of Central Eurasia are studied based on a total of 22 mega- (fruits and seeds, leaves) and 20 microfloras (pollen and spores) compiled from literature. Vegetation is interpreted at the level of plants functional types (PFTs) using a system including 26 classes and an aquatic functional type. The obtained ecospectra showing diversity of PFTs are interpreted in three time slices, namely the early Oligocene, early Miocene and late Pliocene/early Pleistocene. Our results confirm the presence of diverse mixed forests (Turgai type) in the study area throughout the late Paleogene and early Neogene, partly, raised diversity of herbaceous components, especially of dry herbs, and the presence of xeric shrub PFTs points to more open plant cover. The late Pliocene/early Pleistocene spectra from the central and southern latitudinal zones of the study area confirm the existence of open landscapes in general, but partly have a considerable arboreal diversity excluding the presence of mere steppe. Ecospectra obtained from the diversity of functional types have a characteristic representativeness depending on the organ types considered in each case, and therefore have a delimited comparability. Our results show that PFT diversities obtained from microfloras are most suitable in estimating the openness of landscape and in representing zonal biomes in general. The vegetational patterns reconstructed based on the ecospectra of fossil floras basically support the results obtained from previous palaeoclimate reconstructions evidencing cooling and drying of the continental interior of Eurasia throughout the later Neogene. Moreover, the PFT approach is proven more sensitive to identify seasonal drought when compared to other, taxonomy based climate reconstruction methods. Moreover, a first attempt is made to quantify latitudinal temperature gradients for the study area. Data indicate that the Oligocene and early Miocene gradients where shallow and almost identical while the late Pliocene/early Pleistocene gradient was intermediate between the earlier Neogene and the modern one.