Oligocene vegetation of Europe and western Asia—Diversity change and continental patterns reflected by plant functional types

Spatial vegetation patterns potentially reflect coeval continental climate variations which are also impacted by palaeogeographical settings. Plant functional types (PFTs) and their distribution, frequently applied in ecological studies and biome modelling, serve as a tool for reconstructing palaeovegetation units and ultimately tracing palaeoecological/climate gradients. Earlier quantitative studies focusing on distribution patterns of PFTs and designed to put forward data-model comparisons were carried out on well-dated Middle and Late Miocene floras. Moreover, the PFT approach has been successfully applied to reconstruct Eocene vegetation patterns in several time slices at a global scale as well as in regional vegetation reconstructions throughout the Cenozoic. In the current study, a PFT approach with 41 different classes is applied on Rupelian and Chattian fossil floras of Europe and western Asia to infer spatial vegetation differences across the study area. A comprehensive palaeobotanical record including ~163 macro- (leaves, fruits and seeds) and microfloras was compiled. The floristic components of these palaeofloras are translated to PFTs including herbaceous to arboreal classes. The PFTs are defined using traits and climatic thresholds of key taxa, and comprise species assigned by morphological and phenological features with respect to the related ecosystem. Diversity values of each PFT are calculated for the fossil floras and spatial gradients over western Eurasia are investigated for the Rupelian and Chattian. PFT diversity maps and transects for both time slices reveal basic patterns of the vegetational structure at the continental scale. It is shown that in both time slices studied tropical and broadleaved evergreen PFTs were more diverse in the West and at lower latitudes. Consistently with the global climate evolution as known from marine archives and regional continental records their level was higher in the Rupelian compared to the Chattian. All over low diversities of xeric PFTs coincide with the previously assumed dominance of humid climate conditions in western Eurasia throughout the Oligocene, however, the reconstructed spatial gradients suggest somewhat drier conditions to the southwest and southeast of the study area