Azonal communities of ravine forests are often confined to pristine sites, and represent habitats with species-rich biota. Despite their significance for conservation biology, little attention has been paid to this vegetation in the Caucasus, one of the global biodiversity hotspots. Aims: (a) to describe the variability, ecology, and distribution patterns of ravine forests at lower elevations of Colchis in Georgia; (b) to examine the syntaxonomic position of Colchic and Caucasian ravine forests; and (c) to outline the relationships between the identified vegetation types and environmental as well as biogeographic factors. Study area: Georgia, Türkiye. Methods: Two classification analyses (beta-flexible clustering) were performed; the first on vegetation plots of ravine forests (n = 45) from Georgian Colchis, the second on an extended dataset (n = 134) that included additional plots of Caucasian ravine forests and the alliance Alnion barbatae.NMDS was applied to visualize patterns of similarity among the communities. Results: Three associations of Colchic ravine forests were distinguished, mainly reflecting the climate and bedrock: Polysticho woronowii-Ulmetum glabrae (wet climate, volcanics), Pterido creticae-Tilietum begoniifoliae (wet climate, limestones), and Polysticho aculeati-Tilietum begoniifoliae (drier climate, limestones). The classification of the extended dataset resulted in two main clusters, Colchic alluvial forests (Populetalia albae) and scree and ravine forests (Aceretalia pseudoplatani). A further partitioning distinguished between Caucasian and Colchic ravine forests. The latter represent a newly established alliance Pterido creticae-Tilion begoniifoliae, characterised by a wealth of Colchic endemic and relict species. These forests are of particular importance for safeguarding the Colchic forest biota. Conclusions: The variability of the Colchic ravine forests primarily reflects site-specific and climatic conditions, which allow their classification into three distinct associations. These stands constitute a novel alliance which complements the so-far known vegetation diversity of the prominent Colchic forests, a hotspot of Tertiary relict flora in the Northern Hemisphere.<br> Taxonomic reference: Euro+Med PlantBase (https://europlusmed.org/) [accessed 10 Oct 2024].<br> Syntaxonomic reference: Higher syntaxa follow Mucina et al. (2016), exceptions and associations are accompanied by their author citations at the first mention.<br> Abbreviations: DCA = Detrended Correspondence Analysis; GIVD = Global Index of Vegetation-Plot Databases; NMDS = Non-Metric Multidimensional Scaling; TWINSPAN = Two Way Indicator Species Analysis.
