Rocks and outcrops colonised by pioneer communities, especially of Crassulaceae. Vegetation of the alliance Sedo-Scleranthion biennis. Substrates are mostly siliceous, occurring in the upland and montane levels of the nemoral zone. The communities are dominated by succulent Sempervivum, Jovibarba and Sedum species accompanied by Silene rupestris, Erophila verna, Scleranthus polycarpos, Veronica fruticans, Thymus praecox ssp. polytrichus, Viola tricolor ssp. saxatilis, by small crucifers, lichens and mosses Polytrichum piliferum and Racomitrium canescens.