Syntaxonomical survey of mesophilous broad-leaved forests of the alliance Aceri campestris–Quercion roboris Bulokhov et Solomeshch in Bulokhov et Semenishchenkov 2015 on the South-West of Russia

Mesophilous broad-leaved forests predominating in south-western part of Russia were included in alliance Aceri campestris–Quercion roboris Bulokhov et Solomeshch in Bulokhov et Semenishchenkov 2015, association Fraxino excelsioris–Quercetum roboris Bulokhov et Solomeshch 2003 and three geographic subassociations. The subassociation F. e.–Q. r. typicum Bulokhov et Solomeshch 2003 in Bulokhov et Semenishchenkov 2015 unites communities occurring mainly in the broad-leaved forests zone of the Central Russian Upland. The subassociation F. e.–Q. r. stellarietosum nemori Semenishchenkov et al. 2015 occurs in the northern part of the association range in the zone of broad-leaved forests and close to the southeastern border of the hemiboreal subzone. Mesophilous broad-leaved forests occurring in the forest-steppe zone of the Central Russian Upland were included in the subass. F. e.–Q. r. crataegetosum curvisepalae Semenishchenkov in Bulokhov et Semenishchenkov 2015. The geographical distribution of the syntaxa is related to the climate continentality gradient — from the subass F. e.–Q. r. crataegetosum curvisepalae (the largest continentality indices) to the subass. F. e.–Q. r. stellarietosum nemori (the smallest continentality indices). The associations Aceri campestris–Tilietum cordatae Zaugolnova et Braslavskaya 2003 (nom. inv.) from the Kaluga and Tula Regions (Zaugolnova, Braslavskaya, 2003) and Aceri campestris–Quercetum roboris (nom. inv.) (var. Acer tataricum) described from the Voronezh Region (Starodubtseva, Khanina, 2009) were included in the association Fraxino excelsioris–Quercetum roboris after comparative syntxonomical analysis. On the basis of a comparative analysis, diagnostic combinations of subassociations were compiled, consisting of species with constancy above 20 % and values of the statistical φ-coefficient for selections above 20: F. e.–Q. r. stellarietosum nemori — Carex sylvatica (5059.9), Equisetum hyemale (2842.3), Galeobdolon luteum (10087.4), Matteucia struthiopteris (4257.7), Ranunculus cassubicus (5857.9), Stellaria nemorum (3349.6); F. e.–Q. r. crataegetosum curvisepalae — Acer tataricum (5362.0), Crataegus rhipidophylla (5964.0), Poa nemoralis (2736.9), Pyrus pyraster (3840.8), Scilla siberica (4558.4), Viola odorata (3440.5). Analysis of the differentiaal table of mesophilous broad-leaved and spruce-broad-leaved forests syntaxa made it possible to conclude that associations previously (Onyshchenko, 2009) assigned in Ukraine to alliance Scillo sibericae–Quercion roboris have a high floristic similarity with the syntaxa of Aceri campestris–Quercion roboris from the South-West of Russia, especially in the forest-steppe part of its range. Selections of three subassociations of the association Mercurialo perennis–Quercetum roboris from Ukraine floristically close to the syntaxa of alliance Querco roboris–Tilion cordatae from the South-West of Russia. In the dendrogram of cluster analysis, the compared syntaxa are grouped into two blocks corresponding to the rank of alliances: Aceri campestris–Quercion roboris and Querco roboris–Tilion cordatae. Based on the review, the authors believe that the «Hierarchical floristic classification system…» (Mucina et al., 2016) may be amended in terms of recognizing the syntaxonomical independence of the alliance Aceri campestris–Quercion roboris and its geographical interpretation. Derivative communities disturbed by humans in the place of mesophylous broad-leaved forests are classified as anthropogenic variants and non-rank «communities» named after the dominant species: Betula pendula, Populus tremula, Tilia cordata. Forests with a poor floristic composition, in which the diagnostic species of association and subassociation drop out of the coenoflora are classified as inops variants. They are characterized by a noticeable decrease in the average floristic saturation in comparison with typical communities. Derivative forests with a predominance of Betula pendula have a higher species richness in comparison with aspen or linden forests, as well as typical phytocoenoses of the association.