Phytogeography of parasteppic vegetation in the high Friulian Plain (NE Italy)

Abstract

The vascular flora of pedologically conditioned, extensive dry grasslands occurring in a very rainy area of northeastern Italy, was submitted to phytogeographic analysis. The distributional ranges of 144 species were digitized into two presence-absence matrices of species and Operational Geographic Units (quadrants), one covering Europe, the other, limited to 56 species with extra-European distributions, extended to the Northern Hemisphere north of the Tropic of Cancer. These matrices were submitted to numerical classification, obtaining clusters of species with similar distributional patterns (chorotypes). For each cluster of species, the percent occurrencies in each quadrant were processed by a program of automatic mapping, producing a series of isoporic maps showing the joint distribution of the species of each cluster. The species can be subdivided into six main phytogeographical groups: (1) Narrow-ranging (34% of the total), including the endemic, subendemic, Illyrian-Balcanic and NW submediterranean elements, (2) Southern European-Submediterranean (18.8%), (3) Wide-ranging European (16.6%), (4) Eastern-Pontic (7.6%), (5) Southern Eurasiatic (10.5%), (6) Northern Eurasiatic (12.5%). The phytogeographic originality of the investigated grasslands is high, with more than one third of the species having narrow distributional ranges. Particularly relevant are the connections with the Balkanic-Illyrian and the eastern Alpine regions.