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Succession

Can a plant really grow in hardened lava?

It can if it is very hardy and tenacious. And that is how succession starts. It begins with a plant that must be able to grow on new land with minimal soil or nutrients.

Ecological Succession

Communities are not usually static. The numbers and types of species that live in them generally change over time. This is called ecological succession . Important cases of succession are primary and secondary succession.

Primary Succession

Primary succession occurs in an area that has never before been colonized. Generally, the area is nothing but bare rock. This type of environment may come about when

  • lava flows from a volcano and hardens into rock.
  • a glacier retreats and leaves behind bare rock.
  • a landslide uncovers an area of bare rock.

The first species to colonize a disturbed area such as this are called pioneer species (see Figure below ). They change the environment and pave the way for other species to come into the area. Pioneer species are likely to include bacteria and lichens that can live on bare rock. Along with wind and water, they help weather the rock and form soil. Once soil begins to form, plants can move in. At first, the plants include grasses and other species that can grow in thin, poor soil. As more plants grow and die, organic matter is added to the soil. This improves the soil and helps it hold water. The improved soil allows shrubs and trees to move into the area.

Primary succession, volcanic eruption being colonized by pioneer species

Primary Succession. New land from a volcanic eruption is slowly being colonized by a pioneer species.

Secondary Succession

Secondary succession occurs in a formerly inhabited area that was disturbed. The disturbance could be a fire, flood, or human action such as farming. This type of succession is faster because the soil is already in place. In this case, the pioneer species are plants such as grasses, birch trees, and fireweed. Organic matter from the pioneer species improves the soil. This lets other plants move into the area. An example of this type of succession is shown in Figure below .

Secondary succession, plants growing after a forest fire

Secondary Succession. Two months after a forest fire, new plants are already sprouting among the charred logs.

Climax Communities

Many early ecologists thought that a community always goes through the same series of stages during succession. They also assumed that succession always ends with a final stable stage. They called this stage the climax community . Today, most ecologists no longer hold these views. They believe that continued change is normal in most ecosystems. They think that most communities are disturbed too often to become climax communities.

Summary

  • Ecological succession is the process in which a community changes through time.
  • Primary succession occurs in an area that has never before been colonized.
  • Secondary succession occurs in a formerly inhabited area that was disturbed.

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Use these resources to answer the questions that follow.

  1. How does this resource define ecological succession?
  2. Why does succession occur?
  3. What happens to the other species as the plants in an ecosystem change?
  4. What happens when large organisms die in a climax community?
  5. What factors control what actual species are involved in the succession of an area?

Review

  1. What is ecological succession?
  2. Describe the main difference between primary and secondary succession.
  3. Give two examples of habitats that will go through primary succession.
  4. What is a climax community?
  5. Summarize how ideas about ecological succession and climax communities have changed.

Vocabulary

climax community

climax community

Final stable stage of ecological succession that may be reached in an undisturbed community.
ecological succession

ecological succession

Changes through time in the numbers and types of species that make up the community of an ecosystem.
pioneer species

pioneer species

Type of species that first colonizes a disturbed area.
primary succession

primary succession

Change in the numbers and types of species that live in a community that occurs in an area that has never before been colonized.
secondary succession

secondary succession

Change in the numbers and types of species that live in a community that occurs in an area that was previously colonized but has been disturbed.

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