Is chorological symmetry observable within the forest steppe biome in Hungary? — A demonstrative analysis of floristic data

Biome interfaces are expected to exhibit chorological symmetry, i.e., decreasing trends in the number of species associated with each of the two neighbouring biomes as we progress from one into the other. Our aim was to test for such a pattern within the forest steppe biome, which is a transition zone in itself between the temperate deciduous forests and the steppe biome. Presence of chorological symmetry would provide indirect evidence for the prehuman presence of zonal steppes in the Carpathian basin. We also whished to provide an example with this analysis for drawing biogeographical conclusions based on quantitative species occurrence data, an information source hitherto neglected in Central Europe. Occurrence patterns of forest and steppe species were analysed at the Duna-Tisza köze (Danube-Tisza Interfluve) by the traditional qualitative biogeographic method and by hierarchical classification of predicted spatial pattern based on Generalized Linear Models with logistic link function. Species presences were explained by variables describing spatial orientation. In this approach, an outgroup of sand grassland species was also added to characetrise the discrimination ability of the approach. The quantitative method discriminated the out-group of sand grassland species, providing evidence of its suitability for our purpose. The results of the quantitative investigations were also in accordance with the qualitative evaluation. Surprisingly, forest and steppe species showed similar distributional patterns, i.e., no chorological symmetry was discernable. The quantitative biogeographic approach unveiled important evidence for deciding about the potential presence of zonal steppes in the Carpathian basin. Although the observed similarity of the distribution of forest and steppe species may have multiple reasons, the major cause of the lack of chorological symmetry is most probably the lack of zonal steppe South of the forest steppe biome in the Carpathian basin. Additional explanations include land use pattern and the mountain belt around the basin acting as a refugium in the ice ages