Fig. 1

Hypothetical scenarios of postglacial expansion in the extreme western part of the range of Pinus cembra. a ‘Classic’ temporal scenario of colonization and extinction, based on glacial refugia in the Carpathians or the eastern Alps, and migration through central massifs/valleys with four hypothetical haplotypes (number chosen for the conceptual exercise) illustrating colonization, expansion and extinction processes. b Modern spatial pattern of the hypothetical haplotypes, their main/central (large polygon) and peripheral/fragmented populations (small polygons), their migration routes (arrows), and their eventual extinction or absence of immigration (grey area). c Actual locations of main P. cembra forests in the western Alps (the red dashed line distinguishes main central populations from peripheral/fragmented populations), and locations of first dated supporting subfossils (see Additional file 1). d Schematic illustration of the three hypothetical scenarios explaining the species’ distribution in the western Alps: the ‘Classic’ scenario (Ho1); ‘Southeast Alpine refugia’ scenario (Ho2, based on [25, 26]; and ‘Intra-Alpine southern refugia’ (Ho3 based on [27]). The three scenarios are not exclusive but complementary