The Tilio-Acerion alliance includes azonal forests occurring in ravines, on talus slopes and cliffs, which are composed of the nutrient-demanding trees Acer platanoides, A. pseudoplatanus, Fraxinus excelsior, Tilia cordata, T. platyphyllos and Ulmus glabra. Limes (Tilia spp.) occur mainly on slightly drier sites, while the others prefer wetter sites. Other tree species typical of adjacent zonal forests can also be found mixed in the tree layer. The shrub and herb layers contain nitrophilous and mesotrophic forest species, frequently including ferns. These forests occur throughout the Czech Republic on various bedrock types and are absent only on mountain summits and in flat lowland regions. Most stands are however of limited extent. They are most common in deep river valleys.