The flora varies between islands, based on the natural conditions. On the least thriving islands vegetation is limited to lichen growing on stones. Vegetation typically covers five to ten percent of the ground surface, with notable exceptions under bird colonies where it can reach one hundred percent. Vegetation varies with the altitude: up to there is a belt of grass-moss arctic desert, then moss-lichen arctic desert to , then lichen arctic desert up to and above lifeless snow desert, with occasional lichens on nunataks and snow algae on glacier surfaces.