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).