Biology · 12th Grade · Ecological Interactions · Weeks 28-36

Ecological Succession

Examine the processes of primary and secondary succession and their role in ecosystem recovery.

• Common Core State Standards
• HS-LS2-6

About This Topic

Ecological succession describes the predictable sequence of community changes that occur in an ecosystem over time. In US K-12 biology, students distinguish between primary succession , which begins on bare, lifeless substrate such as exposed bedrock after a glacier retreats , and secondary succession, which follows a disturbance like a wildfire or abandoned agricultural field where soil and seed banks remain. Primary succession can span thousands of years; secondary succession typically plays out over decades.

Pioneer species are central to both processes. Lichens and mosses in primary succession break down rock and accumulate organic material, gradually building conditions that support more complex plant communities. In secondary succession, fast-growing annuals and opportunistic shrubs quickly colonize disturbed soil. As facilitation, tolerance, and inhibition mechanisms operate across succession stages, species diversity typically increases toward a climax community , though the concept of a single stable endpoint has been revised in modern ecology.

Active learning works especially well here because succession unfolds over timescales students cannot directly observe. Simulation activities, case-study analysis of real sites like Mount St. Helens or the Chicago Wilderness, and structured data interpretation let students reason through change over time without waiting centuries for results.

Key Questions

1. Explain how primary succession differs from secondary succession in terms of time and species composition.
2. Analyze the role of pioneer species in initiating ecological succession.
3. Predict the long-term changes in species diversity during different stages of succession.

Learning Objectives

• Compare and contrast the initial conditions, rates of change, and dominant species present during primary and secondary ecological succession.
• Analyze the role of pioneer species in facilitating the establishment of later successional communities.
• Predict the trajectory of species diversity and biomass accumulation through different stages of succession in a given ecosystem.
• Evaluate the impact of specific disturbances, such as volcanic eruptions or deforestation, on the process of ecological succession.

Before You Start

Ecosystems and Biomes

Why: Students need a foundational understanding of what constitutes an ecosystem and the characteristics of different biomes to understand how they change over time.

Population Ecology

Why: Understanding population growth, carrying capacity, and interspecific competition is crucial for analyzing how different species interact and replace each other during succession.

Key Vocabulary

Ecological Succession	The gradual process by which ecosystems change and develop over time, involving the replacement of one community of organisms by another.
Primary Succession	Ecological succession that begins in an environment devoid of life and soil, such as on bare rock or sand dunes.
Secondary Succession	Ecological succession that occurs in an area where a community previously existed but has been removed by a disturbance, such as fire or logging.
Pioneer Species	The first species to colonize a barren or disturbed environment, often hardy plants like lichens or grasses that help create soil and modify conditions for other species.
Climax Community	A stable, mature ecological community that represents the final stage of succession for a particular environment, though this concept is now viewed as dynamic.

Watch Out for These Misconceptions

Common Misconception

Succession always ends at a single stable climax community that never changes.

What to Teach Instead

Modern ecology recognizes that disturbance is ongoing and ecosystems are dynamic. A so-called climax community can be reset by fire, drought, or human activity. Having students analyze real longitudinal datasets , rather than idealized diagrams , makes this distinction concrete.

Common Misconception

Primary and secondary succession are just faster and slower versions of the same process.

What to Teach Instead

They differ not just in rate but in starting conditions: primary succession lacks soil and a seed bank, requiring physical substrate modification before plants can establish. Active case-study comparison of volcanic islands versus burned forests helps students see why these are qualitatively different, not just quantitatively different.

Common Misconception

Pioneer species are always plants.

What to Teach Instead

In aquatic and terrestrial systems alike, pioneer organisms can be bacteria, fungi, lichens, or algae , organisms that tolerate extreme conditions and begin nutrient cycling. Gallery walks using diverse photo evidence (not just lichen-on-rock textbook images) broaden students' understanding.

Active Learning Ideas

Gallery Walk: Before and After Succession Photos

Post paired photo sets around the room showing sites at different succession stages (e.g., Mount St. Helens 1980 vs. 2005 vs. today; old-field succession in the eastern US). Student pairs rotate, recording species present, estimated stage, and key evidence at each station. Groups then share observations and build a class timeline on the board.

35 min·Pairs

Think-Pair-Share: Pioneer Species Trade-offs

Pose a scenario: a wildfire burns through a forest. Ask students individually to identify three characteristics a pioneer species would need to survive and reproduce first. Pairs compare lists, then the class consolidates a ranked list with reasons. Follow with a brief reading on nitrogen-fixing bacteria in early succession to test their predictions.

20 min·Pairs

Jigsaw: Succession Case Studies

Assign small groups one of four case studies , Krakatoa recolonization, Yellowstone post-fire, Great Lakes sand dune succession, and Chesapeake Bay seagrass recovery. Each group reads their case, identifies succession type, key species, and rate of change, then teaches the class. Conclude with a structured comparison chart students complete individually.

50 min·Small Groups

Data Analysis: Species Diversity Across Time

Provide students with species richness and evenness data from longitudinal field studies at multiple succession stages. Students graph the data, identify trends, and write a claim-evidence-reasoning paragraph predicting what happens to diversity at the climax stage. Debrief as a class to address contradictions between datasets.

30 min·Individual

Real-World Connections

• Restoration ecologists use principles of succession to guide the replanting and recovery of areas damaged by mining operations or oil spills, aiming to re-establish native plant and animal communities.
• National Park Service rangers monitor the recovery of ecosystems after wildfires, like those in Yellowstone, to understand how plant and animal populations will change over decades and inform future management strategies.
• Urban planners consider secondary succession when deciding what to do with abandoned industrial sites or vacant lots, observing how nature reclaims these spaces and planning for green infrastructure or development.

Assessment Ideas

Quick Check

Present students with two scenarios: one describing bare rock exposed by a retreating glacier, and another describing a forest after a wildfire. Ask them to write one sentence for each scenario identifying the type of succession and one sentence explaining why they chose that type.

Discussion Prompt

Facilitate a class discussion using the prompt: 'Imagine a large area of rainforest is cleared for cattle ranching. What types of species would you expect to see in the first year, after 10 years, and after 100 years? Explain the role of facilitation and inhibition in these changes.'

Exit Ticket

Provide students with a list of species (e.g., lichen, moss, grass, shrub, young pine tree, mature oak tree). Ask them to arrange these species in the order they would likely appear during primary succession and then again during secondary succession, briefly justifying their arrangement for each.

Frequently Asked Questions

What is the difference between primary and secondary succession?

Primary succession begins on substrate with no existing soil or organic matter, such as bare rock after glacial retreat. Secondary succession occurs where soil and a seed bank remain after a disturbance like fire or farming. Primary succession takes much longer because pioneer organisms must first build soil conditions that support larger plant communities.

What role do pioneer species play in ecological succession?

Pioneer species colonize bare or disturbed environments first. They tolerate harsh conditions , low nutrients, temperature extremes, poor soil , and through their growth and decomposition, begin building organic matter and stabilizing substrate. This physical and chemical modification gradually creates conditions that support later-successional species that could not survive the initial environment.

How does species diversity change during succession?

Species diversity generally increases through early and middle stages of succession as habitat complexity grows and more niches become available. In some late-successional systems, diversity may plateau or even decline slightly as dominant species competitively exclude others. Real-world patterns vary considerably by ecosystem type and disturbance history.

How can active learning help students understand ecological succession?

Succession spans timescales beyond any classroom observation window, making direct experience impossible. Active approaches , case-study analysis, longitudinal data graphing, and structured photo comparisons , let students reason through change over time using real evidence. These methods build the pattern-recognition and scientific argumentation skills that rote memorization of succession diagrams cannot.