The importance of environmental difference among sites and dispersal limitations of species to the explanation of diversity differs among biological systems and geographical regions. We hypothesized that climate and then dispersal limitation will predominantly explain the similarity of alpine vegetation at increasing distances between pairs of regions at sub-continental extent. We computed the similarity of all pairs of 23 European mountain regions below 50°N after dividing the species lists of each region by calcareous or siliceous substrates. Distance decay in similarity was better fitted by a cubic polynomial than a negative exponential function, and the fit was better on calcareous than on siliceous substrate. Commonality analysis revealed that the proportion of explanation of beta diversity by climatic difference had unimodal patterns on a gradient of increasing distance between regions, while explanation by dispersal limitation had consistently rising patterns on both substrates. On siliceous substrate, dispersal limitation explained more of the variation in beta-diversity only at longer distances, but it was predominant at all distances on calcareous substrate. The steeper response to distance at <1600 km and >2600 km may indicate dispersal limitation at different temporal scales, and the uptick in the response to distance at the longest distances may reflect how isolated some regions have been before and since the Last Glacial Maximum.

Distance data were derived from a cost-distance surface by Jiménez-Alfaro, B., S. Abdulhak, F. Attorre, A. Bergamini, M.L. Carranza, A. Chiarucci, A., R. Ćušterevska, S. Dullinger, R.G. Gavilán, G. Giusso del Galdo, N. Kuzmanović, P. Laiolo, J. Loidi, G.P. Malanson, C. Marcenó, D. Milanović, E.R. Pansing, J.V. Roces-Díaz, E. Ruprecht, J. Šibik, A. Stanisci, R. Testolin, J-P. Theurillat, K. Vassilev, W. Willner, M. Winkler. 2021. Postglacial determinants of regional species pools in alpine grasslands. Global Ecology and Biogeography 30: 1101-1115. 

Climate differences were derived from principal components analysis of data from CHELSA v1.2. (CHELSA; https://envicloud.wsl.ch/#/?prefix=chelsa%2Fchelsa_V1 and at Dryad: http://dx.doi.org/doi:10.5061/dryad.kd1d4)

Vegetation similarity was derived using Beta-Simpson similarity from Baselga, A. and F. Laprieur. 2015. Comparing methods to separate components of beta diversity. Methods in Ecology and Evolution 6: 1069-1079 applied to the regional vegetation data with Jiménez-Alfaro, B., S. Abdulhak, F. Attorre, A. Bergamini, M.L. Carranza, A. Chiarucci, A., R. Ćušterevska, S. Dullinger, R.G. Gavilán, G. Giusso del Galdo, N. Kuzmanović, P. Laiolo, J. Loidi, G.P. Malanson, C. Marcenó, D. Milanović, E.R. Pansing, J.V. Roces-Díaz, E. Ruprecht, J. Šibik, A. Stanisci, R. Testolin, J-P. Theurillat, K. Vassilev, W. Willner, M. Winkler. 2021. Postglacial determinants of regional species pools in alpine grasslands. Global Ecology and Biogeography 30: 1101-1115. (at Dryad: doi:10.5061%2Fdryad.0cfxpnw1h).

Empty cells are for regions without calcareous substrate.