Quaternary disappearance of tree taxa from Southern Europe. Timing and trends

A hundred pollen and plant macrofossil records from the Iberian Peninsula, Southern France, the Italian Peninsula, Greece and the Aegean, and the southwestern Black Sea area formed the basis for a review of the Quaternary distribution and extirpation of tree populations from Southern Europe. Following a discussion of the caveats/challenges about using pollen data, the Quaternary history of tree taxa has been reconstructed with attention to Taxodium/Glyptostrobus, Sciadopitys, Cathaya, Cedrus, Tsuga, Eucommia, Engelhardia, Carya, Pterocarya, Parrotia, Liquidambar, and Zelkova. The timing of extinction, distributed over the whole Quaternary, appears very diverse from one region to the other, in agreement with current biodiversity in Southern Europe. The geographical patterns of persistence/disappearance of taxa show unexpected trends and rule out a simple North to South and/or West to East trend in extirpations. In particular, it is possible to detect disjunct populations (Engelhardia), long-term persistence of taxa in restricted regions (Sciadopitys), distinct populations/species/genera in different geographical areas (Taxodium type). Some taxa that are still widespread in Europe have undergone extirpation in Mediterranean areas in the lateglacial period and Holocene (Buxus, Carpinus betulus, Picea); they provide an indication of the modes of disappearance of tree populations that may be useful to evaluate correctly the vulnerability of modern fragmented plant populations. The demographic histories of tree taxa obtained by combined palaeobotanical and genetic studies is a most challenging field of research needed not only to assess species/population differentiation, but also to reach a better understanding of extinction processes, an essential task in the current global change scenario.