Diversity Drivers of Inland Saline Vegetation-What Unites Them and Divides Them?

The current knowledge on vegetation of salt-affected habitats has been advanced, calling for a supra-regional assessment. We evaluate the common and distinct features of inland saline/alkaline landscapes of temperate Europe in terms of floristic composition, vegetation types, and abiotic conditions to find out what are the main drivers of their spatial variability and diversity. We delineate 13 subregions with a high occurrence of inland saline/alkaline habitats and by utilizing extensive field surveys in the past 20 years we analyze factors presumably affecting their variability: the size of the area, its proximity to the seacoast, and bioclimatic variables. We subjected them to descriptive statistics and ANOVA; principal components analysis was performed to reduce the number of dimensions for each dataset; correlation analysis was conducted to identify the statistical dependence between the diversity of subregions and observed factors. Despite the general uniformity typical for saline habitats, we observed that the subregions exhibit significant dissimilarity. Among the 107 autochtonous plant specialists, they have in common only one obligate and five facultative halophytes (Puccinellia distans agg.; Carex distans, Juncus gerardi, Lotus tenuis, Schoenoplectus lacustris subsp. glaucus and Trifolium fragiferum). The size of the subregion and its distance from the nearest seas did not affect the overall variability. Higher halophyte richness is driven by the broader range of abiotic and biotic prerequisites, especially the specific climate featuring summer evaporation causing various salinization levels in the soil, which is the most pronounced in the central subregions of the Pannonian Lowland. In its peripheries, the effect of specific conditions is lower, generating a reduced richness of halophytes, and in the subregions of the North German and Polish Plain and the Transylvanian Basin, the edaphic conditions (salt springs from salt deposits) take the main role, resulting also in a decreased halophyte richness and variability.