Data from: Extending glacial refugia for a European tree: genetic markers show that Iberian populations of white elm are native relicts and not introductions

Conservation policies usually focus on in situ protection of native
populations, a priority that requires accurate assessment of population
status. Distinction between native and introduced status can be
particularly difficult (and at the same time, is most important) for
species whose natural habitat has become both rare and highly fragmented.
Here we address the status of the white elm (Ulmus laevis Pallas), a
European riparian tree species whose populations have been fragmented by
human activity and is protected wherever it is considered native. Small
populations of this species are located in Iberia, where they are
unprotected because they are considered introductions due to their rarity.
However, Iberia and neighbouring regions in south-western France have been
shown to support discrete glacial refuge populations of many European
trees, and the possibility remains that Iberian white elms are native
relicts. We used chloroplast RFLPs and nuclear microsatellites to
establish the relationship between populations in Iberia and the Central
European core distribution. Bayesian approaches revealed significant
spatial structure across populations. Those in Iberia and south-western
France shared alleles absent from Central Europe, and showed spatial
population structure within Iberia common in recognised native taxa.
Iberian populations show a demographic signature of ancient population
bottlenecks, while those in Central European show a signature of recent
population bottlenecks. These patterns are not consistent with historical
introduction of white elm to Iberia, and instead strongly support native
status, arguing for immediate implementation of conservation measures for
white elm populations in Spain and contiguous areas of southern France.