Middle Miocene (Badenian) vegetation and climate dynamics in Bulgaria and Poland based on pollen data

Abstract

The Miocene represents a time in Eurasia when evergreen and thermophilous dominated Paleogene vegetation was replaced by deciduous and temperate plants. Climatically, it is the transition from a greenhouse to an icehouse world, with the middle Miocene Climatic Optimum as the last warm episode of Earth history. Processes of plant evolution, transformation of vegetation and coenotic structure were significantly forced by both, changes in the global climate system, and also by significant palaeogeographic reorganizations. To give new insight in the middle Miocene evolution of European ecosystems and climate dynamics, we compared plant assemblages from northern Bulgaria and southern Poland (southern Paratethyan and Polish Lowlands realms).Based on palaeoecological analysis the main palaeocommunities are distinguished in hygro–hydrophytic herbaceous palaeocoenoses (reed marshes), hygrophytic forest palaeocoenoses (swamp forest and bush swamp), riparian forests, and mixed mesophytic forests. Despite some differences in taxonomic composition of these fossil floras and the proportion of individual taxa the vegetation shows similar composition and trends through time. The main trend in the vegetation dynamics is a general decrease in the abundance of palaeotropic and thermophilous elements of semi-evergreen forests. Together with these changes is a corresponding increase in the role of arctotertiary species in plant communities, and these plants became dominant in the mesophytic forests. Changes in swamp vegetation are climatically related too, but these reflect mainly local environmental dynamics and changes in inundation of the basin. Climate data from Bulgaria and Poland lack significant latitudinal climate gradient, thus confirming more or less homogenous climatic conditions within Europe in the middle Miocene.