Mixed forests of Ulmus glabra, Acer campestre, Acer opalus, Fraxinus excelsior, Fagus sylvatica, Quercus petraea, Quercus robur, Tilia cordata, Tilia platyphyllos, Sorbus aria, Sorbus mougeotii, Alnus glutinosa, Pinus sylvestris, Hedera helix, with an understorey comprising numerous shrubs, such as Corylus avellana and Crataegus monogyna, and a rich and luxuriant herb layer including numerous ferns, characteristic of the bottom colluvions of steep, shaded valleys, canyons and gorges of the collinar to montane levels of the Pyrenean and Cantabrian ranges.