RECONSTRUCTION OF OLIGOCENE VEGETATION PATTERNS OF THE NORTH HEMISPHERE BASED ON THE CENOZOIC ANGIOSPERM DATABASE

Oligocene is considered a transition from the archaic world of the tropical Eocene to the more modern ecosystems of the Miocene. Many dramatic physical and biological changes occurred in this epoch, such as the dramatic drop in temperature and CO₂ concentration, a notable extinction event in fauna and expansion of grasses into more open habitats. However, a general picture of the Oligocene vegetation in time and space is still lacking. In this study, we reconstructed the vegetation types of the North Hemisphere during the Oligocene using the Integrated Plant Record vegetation analysis. Fossil data from 125 macrofossil sites is derived from our new fossil database, the Cenozoic Angiosperm Database. The results show that, during the early Oligocene, Europe was dominated by broad-leaved evergreen forests which is similar to the late Eocene. Central to East Asia was dominated by broad-leaved deciduous forests or mixed mesophytic forests while North America was dominated by mixed mesophytic forests. There is no evidence for the xeric open woodland and xeric grasslands or steppe. During the late Oligocene, there was a dramatic decrease of evergreen elements. Consequently, Europe was dominated by Ecotone "MMF" / "BLEF" rather than broad-leaved evergreen forests. Central Asia was dominated by broad-leaved deciduous forests and three fossil sites were reconstructed as xeric grasslands. East Asia and North America in the middle latitudinal regions were still dominated by broad-leaved deciduous forests to mixed mesophytic forests and the low latitudinal regions of East Asia were dominated by broad-leaved evergreen forests.