Ecological succession is the process by which the mix of species and habitat in an area changes over time. Gradually, these communities replace one another until a “climax community”—like a mature forest—is reached, or until a disturbance, like a fire, occurs.
Ecological succession is a fundamental concept in ecology. The study of succession was pioneered at the University of Chicago by Henry Chandler Cowles, who was also one of the founders of ecology as a discipline, as he studied the plants of the Indiana Dunes.
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What is ecological succession?
Ecological succession is the process by which natural communities replace (or “succeed”) one another over time. For example, when an old farm field in the midwestern U.S. is abandoned and left alone for many years, it gradually becomes a meadow, then a few bushes grow, and eventually, trees completely fill in the field, producing a forest.
Each plant community creates conditions that subsequently allow different plant communities to thrive. For example, early colonizers like grasses might add nutrients to the soil, whereas later ones like shrubs and trees might create cover and shade. Succession stops temporarily when a “climax” community forms; such communities remain in relative equilibrium until a disturbance restarts the succession process.
In this video from the National Park Service, Tim Watkins and Robert Boyd explore the Indiana Dunes, learning about its history as an important case study for the development of ecological succession theory.
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.
For example, many natural communities in North America have adapted to periodic disturbances from wildfires: This can help maintain prairie or savanna communities that depend on open habitat and nutrient cycling that might occur as a result of fire.
What are primary and secondary ecological succession?
There are two major types of ecological succession: primary succession and secondary succession.
Primary succession happens when a new patch of land is created or exposed for the first time. This can happen, for example, when lava cools and creates new rocks, or when a glacier retreats and exposes rocks without any soil. During primary succession, organisms must start from scratch. First, lichens might attach themselves to rocks, and a few small plants able to live without much soil might appear. These are known as “pioneer species.”