Biology · Ecology

Ecological Succession

How communities change over time

Ecological succession describes the gradual change in species composition and environmental conditions within an ecological community.

BAREPIONEERSSHRUBS / GRASSMATURE COMMUNITY community composition changes over time
Start Here

What Is Ecological Succession?

Ecological succession is the gradual change in the species composition and structure of an ecological community over time. As organisms arrive, establish, interact, and modify their environment, the conditions of the community can change.

The Big Idea

Succession is a process of community change over time, not simply the replacement of one organism by another.

BAREPIONEERSSHRUBS / GRASSMATURE COMMUNITY community composition changes over time
A simplified succession sequence. Real ecosystems do not always follow exactly the same pathway.
Type 1

Primary Succession

Primary succession begins in an area where little or no soil is present. Examples include newly exposed rock after glacial retreat or newly formed volcanic surfaces.

Pioneer organisms can establish under harsh conditions and help change the environment. Over time, soil develops and conditions can become suitable for additional organisms.

Type 2

Secondary Succession

Secondary succession occurs after a disturbance when soil remains. Examples include recovery after some wildfires, storms, logging, or the abandonment of agricultural fields.

PRIMARY SUCCESSIONSECONDARY SUCCESSION BARE ROCK SOIL DEVELOPS DISTURBANCE SOIL REMAINS little or no soil at the startrecovery can begin with existing soil
The key distinction is the starting condition: primary succession begins without developed soil; secondary succession begins with soil remaining.
Test-Day Shortcut

If the question emphasizes that soil remains, think secondary succession.

The Sequence

Stages of Succession

A simplified model may show pioneer organisms followed by grasses and herbs, shrubs, young trees, and a more mature community. These labels are useful for understanding the general pattern, but actual succession varies with climate, disturbance, species, and starting conditions.

BAREPIONEERSSHRUBSYOUNGTREESMATURECOMMUNITY
Think Like an Ecologist

How Communities Change

Organisms do not simply respond to the environment; they can also change the environment. Plants can alter light levels, soil structure, moisture, and nutrient availability. Those changes can make conditions more favorable for some species and less favorable for others.

ORGANISMSgrow + interactENVIRONMENTsoil • light • moistureNEW CONDITIONSdifferent species favored
Succession involves feedback between organisms and their physical environment.
Disturbance

Disturbance and Succession

Disturbances can change the direction or starting point of succession. The most important question is often: What remained after the disturbance?

Soil remains
Secondary succession may occur because organisms can recolonize an already developed soil environment.
Little or no soil remains
Primary succession may occur because soil must develop before a larger community can establish.
A More Careful Model

Is There Always a Climax Community?

Older ecology models often describe succession as moving toward a stable climax community. Modern ecology recognizes that communities can continue changing because of disturbance, climate, species interactions, and other environmental changes.

Important Nuance

For high-school questions, a climax community generally means a relatively stable, mature community. Real ecosystems can remain dynamic.

Watch Out

Common Misconceptions

“Every fire causes primary succession.”
Many fires leave soil behind, so recovery can involve secondary succession.
“Succession means an ecosystem starts completely over.”
Succession is gradual community change, and what remains after disturbance matters.
“Every ecosystem follows exactly the same stages.”
Succession depends on climate, species, disturbance, and starting conditions.
Test-Day Connections

If You See This on a Test...

“Bare rock with no soil.”
Primary succession
“A field is abandoned and soil remains.”
Secondary succession
“Lichens colonize newly exposed rock.”
Pioneer organisms / primary succession
“Species change the conditions of the environment.”
Organism–environment feedback
Check Your Understanding

Quick Practice

1. What distinguishes primary from secondary succession?
Answer: Primary succession begins where little or no soil exists; secondary succession begins where soil remains after disturbance.
2. Why are pioneer organisms important?
Answer: They can establish in harsh conditions and help modify the environment, including contributing to soil development.
3. Why can succession differ between ecosystems?
Answer: Climate, disturbance, species present, and starting conditions vary.
4. Why might a mature community still change?
Answer: Disturbance, climate, species interactions, and environmental changes can continue to alter the community.
Remember These

Key Takeaways

Remember These

Key Takeaways

  • Ecological succession is gradual change in community composition over time.
  • Primary succession begins with little or no soil.
  • Secondary succession begins where soil remains.
  • Organisms can modify environmental conditions, influencing which species establish next.
  • On tests, identify the starting conditions and disturbance history.
Continue Learning
Habitats →Community Interactions →Ecological Levels of Organization →Carrying Capacity →Limiting Factors →Trophic Levels →
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