1. Ecological Succession
Name: _______________________
Date: ________________________
Pd. _______
Ecological Succession
As you read the information on ecological succession, answer the questions in the right column.
Communities are continuously changing. Migration of a new species into a habitat can alter the entire food chain. Major disturbances (both natural and man-made) including volcanic eruptions, tornados, land development, floods, droughts, invasion of species from other areas, and forest fires can suddenly and drastically destroy a community or an entire ecosystem.
The destruction of an ecosystem is followed by a process of sequential rebuilding. This process of community change after the disturbance is called ecological succession. In ecological succession, the community changes over time and new populations slowly replace the existing ones. Ecological succession involves a change in species composition of a community over time following a disturbance. There are two types of succession: primary and secondary.
If the rebuilding of the ecosystem begins in a lifeless area where even soil has been removed, this is called primary succession. Primary succession follows the formation of new land surfaces consisting of rock, lava, volcanic ash, sand, clay, or some other exclusively mineral substrate.
For example, after a volcano erupts and the lava cools the land is completely barren. The essential and dominant characteristic of primary succession is soil building. In the beginning, there is no soil present.
Define the term ecological succession:
What causes ecological succession?
Identify the dominant characteristic of primary ecological succession.
Fig 1: Primary Succession

2. After an ecosystem is destroyed, the first organisms to inhabit a barren area are called pioneer organisms. Pioneer species initiate the recovery following a disturbance in both primary and secondary succession. Pioneer organisms include lichens (a symbiont consisting of algae and fungi) and mosses. These are often introduced to an area as spores in the wind. Pioneers pave the way for later colonists by altering the biotic and abiotic environment For example, they may alter soil stabilization, soil nutrient enrichment, moisture holding capacity, light availability, temperature, and exposure to wind.
In primary succession, soil develops gradually as rocks are eroded and organic matter accumulates from the decomposed remains of the pioneer organisms. The lichens and mosses grow on rocks and release acids that break down the rock to form soil. Once soil is present, pioneer organisms are overrun by other larger organisms such as ferns, grasses, shrubs, and eventually trees. As the organisms die, more soil builds.
One example of primary succession occurred in 1980 when Mt. St. Helens, a volcano in Washington, erupted and destroyed thousands of acres of pristine forest. All that was left of the community was dust and ash. Within a few years, small herbs and shrubs colonized the area, seeds began to germinate, and animals returned. Over a period of time, trees replaced the herbs to form a mature forest.
The process known as secondary succession occurs when an existing community is severely damaged or cleared by some disturbance such as fire, windstorm, or flood. However, in secondary succession, the soil is left intact. One example is a forest cleared for farmland and then abandoned. The farmland may eventually return to a forest.
In 1988, severe fires in Yellowstone National Park destroyed the trees, but left the soil intact. Within a year, the burned areas of Yellowstone were covered with new vegetation.
What is a pioneer organism?
What types of organisms are pioneer species?
What do you think the term “symbiont” means?
Describe how soil develops after the ecosystem has been destroyed.
Explain how the number and types of organism present in the community would change over time.
Compare primary and secondary succession.
Do you think primary or secondary succession would occur more quickly? Explain why.
Fig 2: Mt. St. Helens after the eruption

3. Fig 3: Secondary Succession
In both primary and secondary succession, the community eventually becomes fairly stable, or reaches equilibrium. A stable, mature community that undergoes little or no change in species is a climax community. The climax community is the final stable community that remains after ecological succession. It describes an end product of succession that persists until the ecosystem is once again disturbed by environmental change.
Primary succession involves changing an area from one lacking any community (no plants, animals, insects, seeds, or soil) to one consisting of populations, communities, and ecosystems. There may have been a previous community, but it a disturbance removes or covers the soil this is primary succession.
Secondary succession follows disturbance of an existing community that removes or damages the vegetation, but does not remove, destroy, or cover the soil. Secondary succession starts WITH SOIL; primary succession does not. Therefore, the pioneer plants of secondary succession start from roots or seeds remaining in the soil or from seeds carried in by the wind or animals from surrounding communities. Since the soil is left intact, secondary succession occurs faster than primary succession.
What is a climax community?
What types of organisms would compose the climax community.
How might natural disturbances and human activities, such as deforestation for farming or building, affect the process of succession?

4. Draw a comic showing how the land changes after a disaster in PRIMARY SUCCESSION
Disaster (lava)
Climax Community
Draw a comic showing how the land changes after a disaster in SECONDARY SUCCESSION
Disaster (fire)
Climax Community