Ecological succession describes how community composition changes over time after new habitat forms or after a disturbance. In AP Biology Unit 8, the key distinction is primary succession begins without soil, while secondary succession begins where soil remains after disturbance.
Updated June 4, 2026 · Reviewed by APScore5 Editorial Team
Ecological succession shows how communities change over time after new habitat forms or disturbance occurs.
Quick answer
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What is ecological succession in AP Biology?
Ecological succession is the gradual change in community composition over time after new habitat forms or after a disturbance. Primary succession begins without soil, while secondary succession begins where soil remains.
Short answer
Ecological succession = communities changing over time. Primary = no soil. Secondary = soil remains.
AP exam tip: On ecological succession AP Biology prompts, use the soil test first, then explain how community composition changes over time.
Takeaways
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Ecological Succession Key Takeaways
Ecological succession changes community composition over time.
Primary succession begins where no soil exists.
Secondary succession begins where soil remains after disturbance.
Pioneer species are the first organisms to colonize an area.
Succession often changes biodiversity, soil quality, and community structure.
Secondary succession is usually faster than primary succession.
Shortcut
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Ecological Succession AP Shortcut
Compact reference
No soil = primary succession.
Soil remains = secondary succession.
Pioneer species arrive first.
Lichens and mosses can help build soil.
Fire, farming, hurricanes, and floods usually lead to secondary succession.
Lava flow or glacial retreat usually leads to primary succession.
AP exam clue: Use the soil test first. Then explain how the community changes over time.
Reasoning
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Ecological Succession Reasoning Ladder
1
Identify the disturbance or starting condition
Is the habitat newly formed or disturbed?
2
Ask whether soil is present
No soil suggests primary succession; soil remaining suggests secondary succession.
3
Identify pioneer species
Which organisms colonize first?
4
Track community change
Which species replace earlier species over time?
5
Connect to biodiversity and stability
How do richness, structure, or resilience change?
6
Predict recovery pattern
Will recovery be slow or fast based on soil, seed banks, and disturbance severity?
AP exam clue: Succession questions are about community change, not individual organisms changing.
Succession
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What is ecological succession?
Direct answer: Ecological succession is the process by which the species composition of a community changes over time.
Succession can occur after new land forms.
Succession can occur after disturbance.
Communities change as species colonize, grow, compete, and modify the environment.
Succession can affect biodiversity and ecosystem stability.
AP Biology questions often ask students to distinguish primary and secondary succession.
Facilitation, Inhibition, and Tolerance in Succession
Direct answer: Facilitation, inhibition, and tolerance are models that explain how species interactions influence succession.
Model
Meaning
AP Clue
Example
Facilitation
Early species help later species colonize
Early species improve habitat
Lichens help build soil
Inhibition
Early species prevent or slow later species
Early species block replacement
Dense shrubs reduce tree seedlings
Tolerance
Later species tolerate conditions and eventually dominate
Species replace others without direct help
Shade-tolerant trees grow under canopy
Example
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Primary Succession Example
Scenario: A lava flow cools into bare rock. Lichens colonize the rock, break it down slowly, and add organic material when they die. Over time, mosses, grasses, shrubs, and eventually trees can grow.
No soil at the beginning.
Pioneer species arrive first.
Soil forms slowly.
Community complexity increases over time.
Example
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Secondary Succession Example
Scenario: A forest fire removes many trees but leaves soil, roots, seeds, and microbes. Grasses and small plants grow first, followed by shrubs and young trees. Over time, the forest community may recover.
Soil remains after disturbance.
Recovery is faster than primary succession.
Species return through seed banks, surviving roots, and dispersal.
Community structure changes over time.
Data
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AP Biology Data Patterns for Ecological Succession
Data pattern: Bare rock, no soil, lichens appear first.
What to do: Identify primary succession.
Data pattern: Fire removes plants but soil remains.
What to do: Identify secondary succession.
Data pattern: Species richness increases over time after disturbance.
What to do: Connect succession to biodiversity change.
Data pattern: Soil depth increases over time.
What to do: Explain pioneer species and organic matter buildup.
Data pattern: Early species are replaced by shrubs and trees.
What to do: Explain community change and species replacement.
Data pattern: Recovery is faster when roots, seeds, and soil remain.
What to do: Explain why secondary succession is faster.
Quick check
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Quick Check
Quick Check
Test yourself in 5 seconds
A glacier retreats and exposes bare rock with no soil. Lichens begin growing on the rock. Which process is occurring?
Answer: A — This is primary succession because the community begins on bare rock where no soil exists. Lichens are pioneer species that can help begin soil formation over time.
Mistakes
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Common Ecological Succession Mistakes
Mistake: Confusing primary and secondary succession.
Fix: Use the soil test: no soil = primary; soil remains = secondary.
Mistake: Thinking succession is individual organisms evolving.
Fix: Succession is community composition changing over time.
Mistake: Saying secondary succession always starts with bare rock.
Fix: Secondary succession starts after disturbance where soil remains.
Mistake: Forgetting pioneer species.
Fix: Pioneer species colonize early and can change conditions for later species.
Mistake: Assuming succession always follows one exact path.
Fix: Succession depends on climate, soil, species, disturbance, and interactions.
Mistake: Calling every disturbance primary succession.
Fix: Many disturbances leave soil, causing secondary succession.
FRQ tips
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Ecological Succession FRQ Strategy
Direct answer: For ecological succession FRQs, identify the starting condition, determine whether soil is present, classify primary or secondary succession, and explain how community composition changes over time.
The starting condition is ____. This is ____ succession because ____. Pioneer species such as ____ may ____. Over time, the community changes as ____.
Scoring checklist
Identifies the starting condition.
States whether soil is present.
Correctly classifies primary or secondary succession.
Two sites are studied after disturbance. Site A is a cooled lava field with no soil. Site B is a burned forest where soil, roots, and some seeds remain.
(a) Identify the type of succession occurring at Site A. (1 pt)
(b) Identify the type of succession occurring at Site B. (1 pt)
(c) Explain why succession is likely faster at Site B. (2 pts)
(d) Describe one role pioneer species may play at Site A. (2 pts)
Scoring checklist
Identifies the starting condition.
States whether soil is present.
Correctly classifies primary or secondary succession.
Identifies pioneer species if relevant.
Explains community change over time.
Uses evidence from the prompt.
Point rubric
(a) Identify the type of succession occurring at Site A. (1 pt)
(b) Identify the type of succession occurring at Site B. (1 pt)
(c) Explain why succession is likely faster at Site B. (2 pts)
(d) Describe one role pioneer species may play at Site A. (2 pts)
Model answer
Site A is primary succession because it begins without soil.
Site B is secondary succession because soil remains after the fire.
Site B recovers faster because soil, roots, seeds, and microbes remain.
Pioneer species at Site A may help break down rock and add organic matter, allowing soil to form.
Common mistake: Do not classify Site B as primary succession just because a fire occurred.
Flashcards
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Ecological Succession Flashcards
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Ecological succession is the gradual change in community composition over time after new habitat forms or after a disturbance. On the AP Biology exam, succession questions usually ask you to classify primary versus secondary succession and explain how the community changes.
What is primary succession?
Primary succession begins in an area where no soil exists, such as bare rock after a lava flow or land exposed by glacier retreat. Pioneer species like lichens and mosses often arrive first and help soil form slowly over time.
What is secondary succession?
Secondary succession begins after a disturbance in an area where soil remains, such as after a forest fire or abandoned farmland. Because soil, seeds, roots, and microbes may survive, recovery is usually faster than primary succession.
What is the difference between primary and secondary succession?
Primary succession starts without soil, while secondary succession starts where soil is already present after disturbance. The fastest AP Biology shortcut is the soil test: no soil means primary; soil remaining means secondary.
What are pioneer species?
Pioneer species are the first organisms to colonize an area during succession. They often tolerate harsh conditions and can modify the environment—lichens break down rock and add organic matter, making later colonization easier.
Why is soil important in succession?
Soil provides nutrients, water-holding capacity, and anchorage for plant roots. Primary succession is slow largely because soil must form first; once soil develops, grasses, shrubs, and trees can colonize more readily.
Why is secondary succession usually faster than primary succession?
Secondary succession is faster because soil, seed banks, surviving roots, and soil microbes often remain after disturbance. Primary succession must build soil from bare rock or exposed surfaces, which takes much longer.
What causes ecological succession?
Succession occurs when new habitat forms or when disturbance resets or alters a community. Colonizing species compete, modify the environment, and are eventually replaced by later species as conditions change.
How does biodiversity change during succession?
Biodiversity often increases during succession as more species colonize and more niches become available. Early stages may have fewer species; middle stages often gain richness; later stages may have more complex interactions.
How does succession connect to ecosystem stability?
Succession affects ecosystem stability by changing biodiversity, food webs, soil quality, and community structure over time. Recovery after disturbance depends on resilience factors like soil retention, seed banks, and remaining species.
What are facilitation, inhibition, and tolerance in succession?
Facilitation means early species improve conditions for later species; inhibition means early species block or slow later colonizers; tolerance means later species endure conditions and eventually replace earlier ones. AP Biology may ask which model fits a given scenario.
How should I explain ecological succession on an AP Biology FRQ?
Identify the starting condition, state whether soil is present, classify primary or secondary succession, name pioneer species if relevant, and explain how community composition changes over time using evidence from the prompt.
