Whether the distribution and assembly of plant species are adapted to current climates or legacy effects poses a problem for their conservation during ongoing climate change. The alpine regions of southern and central Europe (SACEU) are compared to those of the western US and Canada (WUSAC) because they differ in their geographies and histories. Individual-based simulation experiments disentangled the role of geography in species adaptations and legacy effects in four combinations: approximations of observed alpine geographies vs. regular lattices with the same number of regions (realistic and null representations), and virtual species with responses to either climatic or simple spatial gradients (adaptations or legacy effects). Additionally, dispersal distances were varied using five Gaussian kernels. Because the similarity of pairs of regional species pools indicated the processes of assembly at extensive spatiotemporal scales and is a measure of beta diversity, this output of the simulations was correlated to observed similarity for Europe and North America. In North America, correlations were highest for simulations with approximated geography and location-adapted species; those in Europe had their highest correlation with the lattice pattern and climate-adapted species. Only SACEU correlations were sensitive to dispersal limitation. The southern and central European alpine areas are more isolated and with more distinct climates to which species are adapted. In the western US and Canada, less isolation and more mixing of species from refugia have caused location to mask climate adaptation. Among continents, the balance of explanatory factors for the assembly of regional species pools will vary with their unique historical biogeographies, with isolation lessening disequilibria.

The southern and central Europe data were derived from releve data in the European Vegetation Archive (Chytrý et al. 2016) and extracted for alpine grasslands by Jiménez-Alfaro et al. (2021). These data are already in Dryad at: https://doi.org/10.5061/dryad.0cfxpnw1h.

• Chytrý M., Hennekens, S.M., Jiménez-Alfaro, B., Knollová, I., Dengler, J., Jansen, F., … & Yamalov, S. (2016). European Vegetation Archive EVA: an integrated database of European vegetation plots. Applied Vegetation Science, 19, 173-180.
• Jiménez-Alfaro, B., Abdulhak, S., Attorre, F., Bergamini, A., Carranza, M. L., Chiarucci, A., et al. (2021). Postglacial determinants of regional species pools in alpine grasslands. Global Ecology & Biogeography 30, 1101-1115.

The western USA and Canada dataset was derived from a variety of sources, including theses and regional floras. The species lists for added regions that did not well-differentiate the alpine zone were reduced to those species that were in the alpine zone of at least three of the regions with good differentiation or were linked to the alpine by name (e.g., binomial alpinus or common name “alpine …”). This choice was a compromise between excluding regions and including species as alpine that were not. The species nomenclature was updated and reconciled using the Taxonomic Name Resolution Service (tnrs.iplantcollaborative.org) cross-checked with the UDSA PLANTS Database (plants.sc.egov.usda.gov).

Stored as CSV in Excel and accessible with Apache open office.