The 10 Fagion associations bound to the we,;tern part of Czechoslovakia are conditioned both ecologically and chorologically in their species differentiation as well as geographical distribution. The division of the alliance into suballiances follows primarily the ecological phenomena. Within the Eu-Fagenion the associations form 3 groups conditioned by ecological factors.
The Tilio platyphylli Fagetum, Tilio cordatae Fagetum, Melico-Fagetum and Carici pilosae-Fagetum represent associations of the submontane bell:. The Tilio platyphylli Fagetum is characterized by overlapping of Fagion and Carpinion species and by the absence of any Dentaria species due to chorological causes. The Tilio cordatae-Fagetum does not show any chorological phenomena in the species composition, however, it is limited to central, southern and western Bohemia only. The Melico Fagetum is characterized by dominant Melica uniflora which is absent in the western and southern part of Bohemia. The Melico-Fageturn has even a more limited distribution occurring in northern and eastern Bohemia and in northern and central Moravia only. The Carici pilosae-Fagetum is characterized by Carex pilosa (dominant), Cephalanthera longifolia and Euphorbia amygdaloides; it is confined to the Carpathian province.
The Dentario enneaphylli Fagetum, Dentario glandulosae-Fagetum and Violo reichenbachianae-Fagetum represent a group of vicarious associations of the montane belt. The Dentario enneaphylli-Fagetum occurs mainly in the geographical province ~esk~i vyso~ina. Its eastern limit lies in the westernmost part of the Carpathian province where it forms a special subassociation and contacts the Dentarioglandulosae-Fagetum. The latter association is characterized primarily by Dentaria glandulosa, a Carpathian endemic species. The Violo reichenbachianae-Fagetum is conditioned chorologically by the absence of any Dentaria species; it occurs in the mountains Kru~n6 hory and Doupovsk6 hory only.
The Festuco-Fagetum is the single representant of the third group conditioned mainly by ecological factors.