Primary succession is a type of ecological succession that occurs after an extreme disturbance in an environment that is devoid of vegetation and other organisms. This type of succession begins on rock formations, such as volcanoes or mountains, or in a place with no organisms or soil. Primary succession leads to conditions that are more favorable for vascular plant growth. The early stages of primary succession are dominated by species with small propagules (seeds and spores) that can be dispersed long distances. The early colonizers, often algae, fungi, and lichens, stabilize the substrate. Nitrogen supplies are limited in new soils, and nitrogen-fixing species tend to play an important role early in primary succession. Pioneer species like lichen, algae, and fungi, as well as abiotic factors like wind and water, start to "normalise" the habitat or, in other words, start to develop soil and other important mechanisms for greater diversity to flourish. Primary succession is distinguished from secondary succession, which is the recovery of an existing biological community after a disturbance sets back the community’s ecological structure to an earlier stage. Examples of settings in which primary succession often occurs include lava-sterilized landscapes, newly formed sand dunes, and rocks either deposited or scoured by retreating glaciers, because these places either lack soil or their soil cannot sustain life.