Question: How do broad-leaved ravine forests in SE Europe differentiate phytogeographically? Do they differ from analogous European forests? What is their distribution pattern?

Location: southeastern Europe, Apennine-Balkan province.

Methods: The initial data set of 2189 relevés was stratified geographically and phytosociologically; 614 relevés remaining after stratification were classified with a TWINSPAN and cluster analysis, wich resulted in four clusters and eight subclusters. Average Pignatti indicator values for relevés of each subcluster were subjected to PCA to show ecological relationships among the clusters. The spectra of geoelements and sociological species groups of individual subclusters were calculated to show phytogeographical and sociological relationships between them. The diagnostic species combination was calculated by a fidelity measure (φ-coefficient) and presented in a synoptic table.

Results: Broad-leaved ravine forests in southeastern Europe form a separate group within the European broad-leaved ravine forests. They are well differentiated by the species with a southeast European distribution, as well as by many other species that reflect their different ecological affinities.

Conclusions: The phytosociological and phytogeographical relationships between the Apennines and the Balkan peninsula that have already been recognized for other vegetation types have been confirmed for broad-leaved ravine forests. According to the numerical analysis, two suballiances of broad-leaved ravine forests in southeastern Europe are proposed, both belonging to the alliance Tilio-Acerion: an amphi-Adriatic xerothermophilous suballiance Ostryo-Tilienion platyphylli suball. nova and a mesophilous suballiance Lamio orvalae-Acerenion suball. nova, the latter appearing only on the Balkan Peninsula.

Nomenclature: Tutin et al. (1964–1980); except Stellaria montana Pierrat and Dryopteris affinis (Lowe) Fraser-Jenkins. Fagus moesiaca is included in Fagus sylvatica; syntaxonomy follows Mucina et al. (1993), except for the syntaxa under consideration. New names are based on the nomenclature rules in Weber et al. (2000).