Functional leaf traits and leaf economics in the Paleogene - A case study for Central Europe

Numerous data based on extant vegetation reveal global patterns of relationships between functional leaf traits and climate. Leaf life span (LLS), i.e. evergreen vs. deciduous leaves, represents a central parameter linking functional traits related to the global leaf economics spectrum. Paleogene climate transitions are therefore expected to be reflected by functional leaf traits and leaf economics. In this study, fossil floras from six sites in Central Europe dating back to the Paleocene, late Eocene, Early and Late Oligocene are studied, addressing the following questions: 1) How does leaf economics and LLS change through the Paleogene? 2) How do various functional leaf traits change through the Paleogene, and how do they relate to leaf economics? 3) Are changes in leaf functional traits consistent with climate reconstructions from proxy data? As a proxy for LLS change, leaf mass per area (LMA) was determined indirectly. The results show the late Eocene site to stand out from all other sites, by tending towards lower leaf size/width, higher leaf mass per area (LMA), a tendency towards untoothed leaf margins, a high frequency of looped secondary veins, an almost complete absence of lobed leaves, and a low proportion of toothed pinnate leaves with non-looped secondaries. The LMA peak at the Eocene site is caused by untoothed leaf types tending to higher LMA and by an increase in LMA of toothed leaf types, compared to the Paleocene and Oligocene. The proportion of lobed leaves, which usually tend to lower LMA and therefore to deciduousness, increases from the older to the younger Oligocene sites. The results demonstrate that LMA data are valuable for evaluating functional/ecological contexts of architectural traits of fossil leaves. The results are consistent with a post-Eocene cooling trend with mild winters and the development of a drier season, both favoring a trend towards deciduous vegetation.