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Diversity of wet and mesic grasslands along a climatic gradient on the southern margin of the Pannonian Basin

Questions Which are the main wet and mesic grassland vegetation types along the climatic gradient on the southern margin of the Pannonian basin? Which are the most important environmental gradients that determine their distribution and species composition? Location The southern margin of the Pannonian plain (N and E Slovenia, N Croatia, N Serbia). Methods A database of 2, 575 vegetation plots originally assigned to theMolinio-Arrhenathereteawas compiled. Semi- supervised classification based on theK-means algorithm was applied to assign plots into 12 a- priori alliances and to search for new alliances. Non-metric Multidimensional Scaling (NMDS) ordination with Ellenberg's indicator values and bioclimatic variables were applied to show the influence of ecological conditions on species composition. The plots within each alliance were further classified into associations using the beta flexible method. Results Classification resulted in 12 alliances recognized in the EuroVegChecklist, and two new groups appeared. The first group occurs in the eastern part of the research area, where many ruderal species appear. This group was treated as a new alliance, Salvio nemorosae-Arrhenatherionforming a vicariant syntaxon of the allianceArrhenatherion. The second group occurs in the western part. It is a transitional group between mesic (Arrhenatherion) and wet meadows (Deschampsion) and can be treated asAlopecurion. Besides, three new associations and six new subassociations were described, together with the typification of seven associations and of three subassociations. Numerical analyses revealed floristic, ecological and geographical differentiation among analysed vegetation types. Conclusions The communities showed typical Central European features in the western part, but their floristic and ecological conditions changed towards the eastern part, where the continental influence was more pronounced. The vegetation structure and plant species composition in the studied area were influenced by soil moisture and soil nutrient availability as well as by strong biogeographical and climatic gradients.

environmental gradient, macroclimate, meadows, Molinio-Arrhentheretea, pastures, phytosociology, relevés, vegetation classification

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