With a scattered distribution globally, these young rocky ecosystems are exposed to extreme temperatures, weathering and disturbance, and have limited capacity to retain water and nutrients. Analogues in icy environments belong to T6.2. Productivity and diversity are consequently low. Lichens and mosses are often abundant and important to ecosystem development, slowly building soils through incremental retention of moisture and nutrients. Successional development of soils and vegetation may be interrupted by landslides, eruptions and other mass movements. Small-leaved pioneer shrubs and grasses are sparse, often growing in crevices. The simple foodwebs are comprised mainly of microbes and itinerant organisms, with few resident vertebrates other than reptiles and ground-nesting birds.