Postglacial Genetic Legacies, Demography, and Climate Change: Setting Conservation Priorities for Silver Fir

Aim: Climate change challenges the adaptive capacity of several tree species. This study explores the genetic diversity and past range dynamics of silver fir (Abies alba) with the objective of set hotspots of population diversity and priorities for conservation based on climate change-induced dieback. Location: Mediterranean, Europe Methods: We perform genome-wide analysis by RAD-seq to range-wide 26 A. alba populations. Results: We identified two lineages in the southern range, formed by populations from the Apennine chain, from the west side, and those from the Balkans and Carpathians, from the east side. Northern range populations showed two lineages, with definite genetic differences between the westernmost populations from those from the eastern. Populations from the Northern Balkans and the NE Apennine were situated in the introgression zones between postglacial recolonization routes, indicating their intermediate positions. Regarding demographics, southern populations remained stable as glacial refuges, while northern populations experienced a population decline during the middle Pleistocene due to glaciations. Although the demographic events that shaped the current spatial structure of genetic diversity of silver fir go back to the Pleistocene, human pressure during the Holocene likely led to an abrupt range decline, while recent drought events have caused widespread dieback. Main Conclusions: We provide a generic framework for setting silver fir conservation priorities based on the phylogeographical lineages and current dieback symptoms induced by climate change. Our results support that rear edge populations might be disproportionately important for the adaptive capacity of silver fir under a climate change scenario.