Primary succession is ecological succession that begins in essentially lifeless areas, such as regions in which there is no soil or where the soil is incapable of sustaining life (because of recent lava flows, newly formed sand dunes, or rocks left from a retreating glacier). The first species to arrive are fast-growing “weedy species,” such as lichens or small annual plants, which create the first layers of soil as they decompose. These plants also provide habitats for small animals and other forms of life. These plants are replaced by grasses and shrubs, which shade out the first colonizers and alter the soil further, before large trees and more shade-tolerant species replace the community of sun-loving grasses and shrubs. Each community may support different collections of animal species.
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