Phylogenetic distance
We calculated phylogenetic distances of each tree species within a genus to a genera specific native reference species, namely, Betula pendula , Fraxinus excelsior , Quercus robur and Acer platanoides . The phylogenetic trees and distance calculations in this study were constructed and calculated by using the native reference species, Betula pendul a and Fraxinus excelsio r, as a root (i.e., a phylogenetic distance of zero), and calculating the time of the last divergence event between the most closely related species from the last common ancestor species. The next divergence event was then calculated from the last common ancestor to the following one, and so on. The phylogenetic distances for each studied tree species to the native reference species was extracted from available literature, by using chronograms that displayed the divergence time between species in million years before present (myr). A study from the IranianBetula population was used as a baseline for Betula (Binaet al. 2016), with additions added with the consideration of further studies (Wang et al. 2016) to construct a phylogenetic tree spanning the Betula species considered in this study. The classifications into subgenera and sections follows a taxonomic revision, spanning the whole genus (Ashburner & McAllister 2013). The phylogeny and biogeography of genus Fraxinus is well-resolved and generally accepted in literature, following numerous revisions over the last two decades (Hinsinger et al. 2013; Olofsson et al.2019; Wallander 2008). The phylogenetic tree by Hinsinger et al. (2013) was used as a baseline for Fraxinus , while the classification into sections follows Olofsson et al. (2019), with the omitted sections being included from Hinsinger et al. (2013). To examine phylogenetic distances in the genus Quercus the phylogenies of Xu et al. (2019) and of Pearse & Hipp (2009) were used, for the genus Acerthat of Li et al. (2019).