Tree diversity in the Miocene forests of Western Eurasia

In the present study, published Miocene mega- and microfloral records compiled from a total of 92 localities in Western Eurasia are analysed with respect to diversity of different plant functional types (PFTs). To study spatial diversity patterns and their evolution three time-intervals are selected corresponding to the Langhian (16.3-13.6 Ma), the Serravallian (13.6-11.6), and the earlier part of the Tortonian (11.6-8.5 Ma). First all arboreal species occurring in the floras are classified using a total of 13 different PFTs (functional types of trees and climatically defined subtypes). In a next step, diversity spectra with respect to these PFTs are generated for each site. Cluster analysis is then performed in order to obtain groups of floras with similar spectra that are interpreted in terms of vegetation type. Their spatial distribution in each time-interval is shown in maps. According to these results, zonally arranged patterns are obtained. Broadleaved Deciduous Forests are most important in the higher latitudes while Mixed Mesophytic Forests dominate the mid-latitudes in Western Eurasia. Broadleaved Evergreen Forests are of minor importance in the area of interest. The observed diversity patterns and their changes in time are correlated with spatial climate patterns and the continental palaeoclimate evolution. During the late Miocene cooling, Broadleaved Evergreen Forests completely disappear from the mid-latitudes of Western Eurasia, and Mixed Mesophytic Forests of the mid-latitudes are mostly replaced by broadleaved deciduous vegetation types. In the context of this cooling, a drier season became established in Western Europe during the Tortonian, as is evident from reconstructed arboreal diversity data and precipitation data. In Central Europe, vegetation types indicating permanently humid conditions persisted throughout all the three time-intervals analysed.