Succession in biology refers to the process by which the structure of a biological community changes over time. It is a predictable and inevitable change that occurs in response to changes in the environment. There are two types of succession: primary and secondary. Primary succession occurs in essentially lifeless areas, such as regions in which the soil is incapable of sustaining life due to factors like lava flows, newly formed sand dunes, or rocks left from a retreating glacier. Secondary succession occurs in areas where a community that previously existed has been removed, and it is typified by smaller-scale disturbances that do not eliminate all life and nutrients from the environment.
During succession, the sequential progression of species is not random, and certain species have evolved life histories to exploit the particular conditions of the community. These changes allow other species that are better suited to this modified habitat to succeed the old species, and this process repeats multiple times during succession. At each stage, new species move into an area, often due to changes to the environment made by the preceding species, and may replace their predecessors. Succession often involves a progression from communities with lower species diversity to communities with higher species diversity, though this is not a universal rule.
Understanding how succession happens in a variety of ecosystems and what kinds of disturbances and time spans lead to the formation of different plant and animal communities is important for scientists who want to understand ecosystem dynamics and effectively protect or restore natural communities.
