Postglacial dispersal limitation of widespread forest plant species in nemoral Europe

Climate is often singled out as the primary range limiting factor at large scales, while other environmental factors, notably soil, are thought to predominate at smaller scales. However, the postglacial migrational lag hypothesis controversially suggests that many species are strongly dispersal-limited and still expanding from their ice age refugia. We investigated the importance of postglacial migrational lag, climate, and soil as range determinants for 47 widespread forest plant species across nemoral Europe (47.0-60.0 degrees N, west of 24.0 degrees E) using regression modeling, information-theoretic model selection, multi-model inference, and variation partitioning. Migrational lag was represented by a measure of accessibility to recolonization from ice age refugia. Twelve species were largely ubiquitous and not analyzed further. For the remaining species, there was strong support for climate, soil, and accessibility to postglacial recolonization. Accessibility accounted for a small to moderate amount of variation, but its model-averaged regression coefficient was stronger than those for climate or soil for 11 species and the second or third strongest coefficient for an additional 10 species. The resulting odds ratios were greater than one for 33 out of 35 species, i.e. adjusted for climate and soil, prevalence for the far majority of the 35 non-ubiquitous species increased with increasing accessibility. There were no differences among growth forms in the importance of accessibility. In contrast, compared to non-boreal species, accessibility had little importance for species with wide boreal distributions, as expected from their more widespread, northern glacial distributions. In conclusion, even the ranges of many widespread forest plant species are probably still moderately to strongly limited by postglacial migrational lag. Therefore, although species ranges are also strongly influenced by climate, we cannot expect most forest plant species to closely track the expected 21st century climatic changes.