Investigating the Evolution of Functional Diversity in Trees During Cenozoic Climate Change

The native tree flora of Holocene Europe represents the aftermath of a series of climate-induced extinction events that began with the onset of a global cooling trend in the Middle Eocene (ca. 45 Mya). Step by step, Europe was stripped of its evergreen, thermophilous, and moisture-demanding trees, which are nowadays confined exclusively to tropical and subtropical latitudes. Despite these losses, the succeeding temperate-deciduous tree flora continued to boast high diversity leading up to the Plio-Pleistocene Transition (ca. 2 – 3 Mya). However, during the Pleistocene, repeated glaciations left Central Europe especially depauperated compared to other temperate regions of the Holarctic realm. Within this context, I aim to investigate general trends in the evolution of genus-level functional diversity in trees over the course of the Cenozoic. I test the hypothesis that this ecological re-sorting was not random, rather driven by a high degree of ecological determinism with respect to the selection of useful traits. I expect that gradual cooling will increasingly favour traits related to persistence, whereas the Pleistocene glaciations will increasingly favour traits related to dispersal. With future climate change predicted to pose serious risks to the integrity of European forests, expanding knowledge of how trees have responded to climate-induced extinctions in the past could enable policymakers to craft better strategies for increasing forest resilience.