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Ecological Succession Stages & Processes

Lauren Scott, Joshua Anderson
  • Author
    Lauren Scott

    Lauren has a Bachelor's degree in biology from Virginia Tech and Master's degrees in environmental science & policy and special education from Johns Hopkins University. She has 20 years of teaching experience in public, private, and informal educational settings.

  • Instructor
    Joshua Anderson
Understand ecological succession, the process of ecological succession, and learn about climax succession. Learn to examine the stages in ecological succession. Updated: 09/14/2021

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Ecological Succession

The recovery of plant communities after a dramatic disturbance illustrates nature's resilience. The vegetation gradually returns to a damaged ecosystem, forming populations and communities that change over time. That repopulation process, in which disturbed regions are colonized by organisms that are gradually replaced by new species, is called ecological succession.

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  • 0:05 Ecological Succession
  • 2:13 Chaparral Ecosystems
  • 4:12 Secondary Succession
  • 6:25 Primary Succession
  • 8:19 Lesson Summary
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Process of Ecological Succession

Natural succession occurs through several stages and processes. Succession begins with disruption to an existing environment, followed by increasing organism density and diversity as the region recovers. Ecologists describe environmental succession with the following terms:

  • Initial Conditions (Equilibrium)
  • Disturbance
  • Colonization
  • Competition
  • Succession
  • Climax

These stages and processes involve interactions between plant species and biotic, or living, and abiotic, or nonliving, factors in the environment.

Examining the Stages in Ecological Succession

An in-depth examination of the stages in ecological succession reveals a complex process that is heavily dependent on chance. The timing of each stage, and the species involved, depends on wind direction, weather, human activity, geological events, animal movement, and the species composition of the surrounding environment.

Initial Conditions (Equilibrium)

The initial conditions are those that existed before a significant ecological change. In some ecosystems, this may be a state of equilibrium in which species populations are balanced and stable. The output of primary producers, like plants and algae, strongly influences this balance. Initial conditions may already be unstable due to habitat destruction, loss of apex predators, or other ecological imbalances.

Disturbance

The disturbance is the event that severely damages or destroys the existing ecosystem. This may be a major event, like a volcanic eruption or massive wildfire, or a more minor event like a local flood. Little or no life remains in the area after the disturbance, and abiotic factors like sunlight exposure and soil composition change.

Colonization

Sometime after the disturbance, tiny organisms reestablish themselves in the damaged ecosystem. This return of microscopic organisms and small primary producers is called colonization. The first species to repopulate the environment must be able to tolerate harsh and unstable conditions.

Competition

Colonizing organisms change environmental conditions, including soil composition, allowing new species to establish themselves. As biodiversity, or the number of species in the area, increases, resource competition increases. For example, bushes and shrubs reduce sunlight availability for smaller plants. Shade-tolerant species eventually outcompete plants with greater sunlight requirements.

Succession

The process in which other species replace established species is called succession. The first organisms to colonize the landscape are diminished or eliminated through resource competition, and larger plant species become dominant. If the initial ecosystem contained a diverse community of herbaceous plants, shrubs, and trees, this process might happen in several stages. In ecosystems with fewer plant species, like grasslands and some wetlands, the process has fewer stages.

Climax

The last stage of ecological succession is the formation of a climax community. There is minimal resource competition and no further replacement of dominant plant species.

Types of Ecosystem Succession

The ecological disturbances leading to environmental succession vary and determine how succession starts and progresses. Succession that occurs after a significant geological event, like a glacier retreat or volcanic eruption, is called primary succession. Succession that occurs after a wildfire, clear-cutting, or discontinuation of farming is called secondary succession. Organism colonization happens differently in each succession type due to variations in ecological conditions after a disturbance.

Primary Succession

Primary succession occurs when there is little to no soil left after a significant geological event. Microscopic organisms, like protists, colonize the area first. The first macroscopic organisms are often lichen and mosses that grow from spores carried by the wind. The first colonizing species are called pioneer species and must survive in nutrient-poor conditions. As these pioneer organisms die and decompose, a thin layer of soil forms, supporting herbaceous plants and grasses.

Small plants slowly colonize the rubble field left behind by a retreating glacier.

grass growing over glacier moraine

These small plants contribute to further ecological changes that allow shrubs to grow. In a forest ecosystem recovering from severe disturbance, long-lived trees eventually outcompete the shrubs. The speed of this process relies on many factors, including weather, human interference, and the types of seeds deposited by animals and the wind. It may take hundreds or thousands of years for the ecosystem to approach its original state.

Primary succession reestablished grasses and some trees around Mount Saint Helens 25 years after the eruption.

Primary succession at Mount Saint Helens

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Frequently Asked Questions

What is the climax stage of succession?

The climax stage of succession is the final stage in which the ecosystem is balanced and relatively stable. Species replacement ceases.

How does ecological succession occur?

Ecological succession occurs when environmental changes allow new plant species to outcompete existing plant species in a recovering ecosystem. Plant communities shift and diversify over time.

What are examples of ecological succession?

An example of primary succession is the recovery of the Mount Saint Helens region after the 1980 eruption. Small plants are gradually being replaced by larger ones on ground that was covered in ash. An example of secondary succession is the recovery of chaparral ecosystems after a wildfire. Soil and protected roots remain, allowing plant populations to recover more quickly.

What is ecological succession and its types?

Ecological succession is the slow replacement of plant species by other plant species in a disturbed ecosystem. Primary succession occurs when a natural disaster leaves no topsoil behind. Secondary succession occurs when fires, floods, or human activity remove vegetation but leave the topsoil.

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