Bioregionalization of Albania: Mismatch between the flora and the climate suggests that our models of Southern European bioregions are in need of a revision

Abstract

We analysed the floristic subdivisions of Albania by hierarchical clustering of all the vascular plant species of Albania over a grid of 25 km cells, adapting data from the Vascular Species Distribution Atlas in Albania of ( Barina Z (ed.) (2017) Distribution atlas of vascular plants in Albania. Hungarian Natural History Museum, Budapest). We identified the principal axes of variation of the flora and the bioclimatic variables that explain it. We also analysed the bioclimate of Albania by means of a self-organizing map (SOM) of the main climatic variables and the application of the global bioclimatic model of Rivas-Martínez. We compared the analysis based on the flora with that based on the bioclimate. The results divided Albania into eight floristic units corresponding to the main vegetation types (Carpinus orientalis woodlands, Quercus cerris woodlands, Quercus petraea and Fagus sylvatica woodlands, Quercus coccifera woodlands, Quercus coccifera and Quercus ithaburensis woodlands, Pinus heldreichii woodlands, alpine vegetation of North Albania, and alpine vegetation of eastern Albania). Two main trends of variation can be recognized: four elevational belts, strongly correlated with average July temperature, and a north–south subdivision, weakly correlated with annual rainfall and thermal excursion. The bioclimatic analysis (SOM and Rivas-Martínez model) resolves and adds detail to the axis of the elevational belts but cannot discern the north–south subdivision apart from the high mountains. We obtained a division into eight floristic units ordered according to two gradients: four elevational belts, each in turn subdivided into a north-central and a southern province. These two gradients seem to have a broader meaning in Southern Europe, particularly the north–south subdivision at about 30° latitude. The partial mismatch between the bioclimate and the flora indicates that bioclimatic models of Europe are in need of a revision and suggests that the history, in addition to the present-day climate (for instance, the vegetation of the last glacial maximum), can play a role in shaping the biogeography of Southern Europe.