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Variability and plant communities’ diversity of acidophilous dwarf-heath mountain tundra (the class Loiseleurio-Vaccinietea) in Romanian Carpathians

The paper presents a comprehensive numerical analysis of vegetation within the class Loiseleurio-Vaccinietea Eggler ex Schubert 1960 in Southeastern Carpathians (Romanian Carpathians), specifically the cryophilous dwarf-shrub heathlands on windswept slopes and edges and acidophilous mesophilous dwarf-shrub communities in subalpine and alpine belts. Based on a large dataset of phytosociological relevés stored in the Romanian Grasslands Database (EU-RO-008), this contribution was focused on the variability of dwarf-shrub communities, their environmental preferences, and the main ecological factors shaping their floristic composition. All relevés were analyzed using hierarchical agglomerative clustering methods to identify the main vegetation groups. Direct and indirect ordination methods were used to identify the main gradients affecting the floristic composition of individual vegetation types. The numerical analysis revealed six well-defined communities, largely corresponding to associations described in syntaxonomical literature, according to their diagnostic species: Cetrario-Loiseleurietum procumbentis Br.-Bl. et al. 1939, Cetrario nivalis-Vaccinietum gaultherioidis (Hadač 1956) Hadač ex Šibík et al. 2007, Rhododendro myrtifolii-Vaccinietum Coldea et al. 1981 , Campanulo abietinae-Juniperetum nanae Simon 1966 , Campanulo abietinae-Vaccinietum myrtilli (Buia et al. 1962 ) Boşcaiu 1971 , and Bruckenthalio-Juniperetum nanae (Horvat 1938) Coldea in Coldea et al. 2015. New syntaxa were identified at lower hierarchical levels (sub-associations) and new typifications were made. The floristic composition of target species-poor communities was mainly modelled by altitudinal range (temperature) and bedrock type. In Detrended Correspondence Analysis, the plant communities were arranged based on a gradient of altitude, from those occurring in the harshest environmental conditions, at highest elevations, with a floristic composition rich in heliophile species (alliance Loiseleurio-Vaccinion Br.-Bl. in Br.-Bl. et Jenny 1926) to communities distributed at lower elevations, on sites with higher mean annual temperatures and with a floristic composition rich in shade tolerating species (alliance Juniperion nanae Br.-Bl. in Br.-Bl. et al. 1939). Relevés of alliance Rhododendrion myrtifolii de Foucault ex Theurillat et Mucina in Mucina et al. 2016 were located in an intermediate position within studied communities.