Pinus uncinata forests of the western outer Alps, the Jura and Pyrenean north facing slopes (ubacs), developed on siliceous or decalcified soils of the subalpine level with a predominately ericaceous undergrowh comprising Rhododendron ferrugineum (dominant), Vaccinium myrtillus, Vaccinium uliginosum, Calluna vulgaris, Homogyne alpina, Deschampsia flexuosa, Lycopodium annotinum.
Pinus uncinata forests of north facing slopes (ubacs) of the Pyrenees developed on siliceous soils, or on decalcified soils in the calcareous ranges, in the more humid and snowy parts of the subalpine level, with a ground layer dominated by Rhododendron ferrugineum accompanied by Vaccinium myrtillus, Homogyne alpina, Rosa alpina, Deschampsia flexuosa, Oxalis acetosella, Juniperus nana, Calluna vulgaris, Dryopteris linneana, Polystichum spinulosum, Solidago virgaurea.