Late Quaternary range shifts of marcescent oaks unveil the dynamics of a major biogeographic transition in southern Europe

Marcescent forests are ecotones distributed across southern Europe that host increased levels of biodiversity but their persistence is threatened by global change. Here we study the range dynamics of these forests in the Iberian Peninsula (IP) during the Late Quaternary, a period of profound climate and anthropic changes. We modeled and compared the distribution of eight oak taxa for the present and two paleoclimatic environments, the Last Glacial Maximum (LGM, ~ 21 kya) and the Mid-Holocene (MH, ~ 6 kya). Presence records were combined with bioclimatic and topographic data in an ensemble modelling framework to obtain spatial projections for present and past conditions across taxa. Substantial distribution shifts were projected between the three studied periods, that were explained by precipitation, winter cold and terrain ruggedness. Results were congruent with paleoclimatic records of the IP and showed that range shifts of these contact zones concurred with range dynamics of both Submediterranean and Temperate oaks. Notably, the distribution ranges of hybrid oaks and marcescent forests matched throughout the late Quaternary. This study contributes to unveil the complex Late-Quaternary biogeography of the ecotone belt occupied by marcescent forests and, more broadly, of Mediterranean oaks. Improved knowledge of species’ responses to climate dynamics will allow us to anticipate and manage future range shifts driven by climate change.