Past, present and future distributions of Oriental beech (Fagus orientalis) under climate change projections

Phylogeographic and taxonomic framework and inferred glacial refugia In general, populations of F. orientalis are markedly more differentiated than F. sylvatica L. with FST (coefficient of differentiation among populations) being 0.157 in the former and 0.032 in the latter. In addition, much higher levels of allelic richness in this species indicating that Pleistocene bottlenecks did not deplete the gene pool to the extent they did in the European F. sylvatica [52]. Geographical subgroups of F. orientalis are morphologi- cally and genetically highly distinct [52–56]. Populations ranging from eastern Bulgaria to northern Turkey and the Amanos Mountains form one cluster. Two additional highly dis- tinct clusters involve the Caucasian populations on the one hand and the populations south of the Caspian Sea on the other hand. In contrast, the European F. sylvatica forms a single cluster [52]. In a recent study, Go¨mo¨ry et al. [56] tested speciation scenarios in sub- groups of F. orientalis under an approximate Bayesian framework. The number of genera- tions was used to estimate divergence times between genetically distinct regional populations. Divergence times suggest that European populations of F. sylvatica diverged from Asian Minor populations (F. orientalis) at c. 1.222–0.7 Ma. The Crimean beech is a hybrid between Caucasian F. orientalis and F. sylvatica. It might have originated at around the Eemian interglacial (130–114 ka). Differentiation among the eastern populations hap- pened much earlier: Caspian populations become isolated from Caucasian ones at 2.2–1.6

Ma, and from Turkish ones at 1.9–1.8 Ma. Finally, genetic isolation between populations of F. sylvatica from the Balkans and Central Europe and Apennine occurred much later, at 100 ka and 70 ka. This has important implications for inferring Pleistocene refugia for beech in western Eurasia. Essentially, when considering LGM and MH, in situ refugia must have existed for all geographical subgroups of F. orientalis because these regional groups had been isolated long before these events. Table 1. Correlation matrix between 19 bioclimatic variables. VARIABLES BIO1 BIO10 BIO11 BIO12 BIO13 BIO14 BIO15 BIO16 BIO17 BIO18 BIO19 BIO2 BIO3 BIO4 BIO5 BIO6 BIO7 BIO8 BIO9 BIO1 1,00 BIO10 0,97 1,00 BIO11 0,96 0,87 1,00 BIO12 -0,45 -0,56 -0,29 1,00 BIO13 -0,59 -0,65 -0,46 0,90 1,00 BIO14 -0,21 -0,32 -0,06 0,86 0,60 1,00 BIO15 -0,17 -0,04 -0,31 -0,46 -0,10 -0,77 1,00 BIO16 -0,59 -0,66 -0,46 0,91 0,99 0,60 -0,10 1,00 BIO17 -0,21 -0,32 -0,05 0,87 0,60 0,99 -0,78 0,61 1,00 BIO18 -0,68 -0,68 -0,61 0,82 0,87 0,61 -0,17 0,87 0,61 1,00 BIO19 0,26 0,08 0,44 0,53 0,30 0,64 -0,61 0,30 0,64 -0,02 1,00 BIO2 -0,09 0,00 -0,22 -0,32 -0,25 -0,34 0,50 -0,24 -0,36 -0,23 -0,28 1,00 BIO3 -0,19 -0,29 -0,07 0,23 0,19 0,15 0,05 0,20 0,14 0,01 0,31 0,62 1,00 BIO4 0,19 0,42 -0,09 -0,61 -0,47 -0,55 0,50 -0,47 -0,56 -0,25 -0,64 0,41 -0,44 1,00 BIO5 0,93 0,98 0,80 -0,63 -0,71 -0,40 0,06 -0,71 -0,41 -0,74 0,02 0,20 -0,18 0,49 1,00

BIO6 0,92 0,81 0,99 -0,20 -0,38 0,01 -0,38 -0,38 0,02 -0,54 0,49 -0,37 -0,15 -0,18 0,72 1,00 BIO7 0,03 0,24 -0,23 -0,58 -0,45 -0,56 0,59 -0,45 -0,57 -0,28 -0,62 0,75 -0,05 0,90 0,39 -0,36 1,00 BIO8 -0,15 -0,08 -0,23 0,25 0,33 0,11 0,11 0,32 0,12 0,51 -0,36 -0,08 -0,25 0,25 -0,11 -0,21 0,13 1,00 BIO9 0,81 0,75 0,81 -0,56 -0,67 -0,37 -0,01 -0,66 -0,37 -0,87 0,31 0,14 0,13 0,03 0,78 0,75 0,04 -0,51 1,00 The bioclimatic variables selected for the present study are highlighted in red. https://doi.org/10.1371/journal.pone.0242280.t001 PLOS ONE Species distribution modeling of Oriental beech (Fagus orientalis) PLOS ONE | https://doi.org/10.1371/journal.pone.0242280 November 17, 2020 5 / 19