Succession is the gradual transformation or creation of a biological community as new species move into an area and modify local environmental conditions. Primary succession occurs when plant and animal species colonize a previously barren area, such as a new volcanic island, a sand dune, or recently glaciated ground. In these cases every living thing, from soil bacteria and fungi to larger plants and animals, must arrive from some adjacent habitat. Secondary succession is the development of communities in an area that has been disturbed by fire, hurricanes, field clearing, tree felling, or some other process that removes most plants and animals. Intermediate successional communities are known as "seral stages" or "seres."

As early successional species become established, they alter their environment and make it more habitable for later seral stages. Usually a disturbed or barren area has low soil nutrient levels, intense sunlight, and no protection from...