Vegetation classification of acidophytic oak forests of Romania
The acidophytic oak forests of Romania are well documented with phytosociological data but a critical revision of their ecology and syntaxonomy is still missing. The most recent syntheses of vegetation rely only on expert-based classification. As these results are not fully satisfactory, the methods of multivariate analysis could offer an objective insight into vegetation variability. For that, we gathered from Romanian literature and from our own studies 701 relevés identified as acidophytic or oligotrophic oak forests. A preliminary selection was applied in order to keep only those relevés with a minimum proportion of acidophilous species. The results indicate that many relevés represent not acidophytic but oak-hornbeam vegetation. The final database, comprising 279 relevés, was subjected to divisive classification (TWINSPAN). Three vegetation units are distinguished, corresponding to the following syntaxa: Luzulo luzuloidis-Quercetum - mesic, oligotrophic, in colder areas, Cytiso nigricantis-Quercetum - dry, extreme oligotrophic, Sorbo torminalis-Quercetum - dry-mesic, mesotrophic. The floristic composition reflects the transitional character between acidophytic and xerophytic forests and in this regard is discussed the relationship of the identified associations with the phytosociological alliances - the first two units were subordinated to the alliance Quercion roboris and the third to the alliance Quercion petraeae. The syntaxonomical scheme of acidophytic oak forests, in use in Romania, is being critically revised considering the major monographs published at European level.