[This habitat could not be formally defined in the expert system because it is not based on vegetation.]

This habitat occurs on very exposed summits, ridges and slopes of mountains in the boreal and arctic zones, blown clear of snow in winter and with shallow stony soils, nutrient-poor and usually acidic, that are susceptible to freeze-thaw and sorting. The vegetation is determined by the strong winds and cold and dominated by bryophytes and fruticose lichens. The habitat is generally beyond the limit of pastoral farming but can be grazed by wild herbivores.