Biology · 9th Grade · Ecology and Global Systems · Weeks 28-36

Ecological Succession and Disturbance

Tracing the predictable changes in a community following a disturbance, from pioneer to climax communities.

• Common Core State Standards
• HS-LS2-6
• HS-LS4-5

About This Topic

Ecological succession is the predictable, directional change in community composition following a disturbance. In 9th grade biology, students differentiate between primary succession, which begins on bare substrate with no existing soil (such as on a newly formed volcanic island or glacial moraine), and secondary succession, which begins where a community was disrupted but soil remains (such as an abandoned agricultural field or a post-fire forest site). Pioneer species colonize first and modify the environment in ways that enable later, more competitive species to establish. This aligns with HS-LS2-6 and HS-LS4-5.

The traditional concept of a stable 'climax community' that succession inevitably reaches has been significantly revised by ecologists. Modern disturbance ecology recognizes that most real ecosystems exist in a shifting mosaic of successional stages, shaped by ongoing fire, windstorms, flooding, and other disturbances. Some US ecosystems, including fire-adapted longleaf pine forests of the Southeast and tallgrass prairies of the Midwest, depend on periodic disturbance to maintain their characteristic structure and biodiversity.

Active learning makes succession concrete. When students sequence photographic records from a known disturbance site such as Mount St. Helens or a post-fire Yellowstone watershed, they move from memorizing succession stages to reasoning about the ecological mechanisms that drive community change over time.

Key Questions

1. Differentiate between primary and secondary succession.
2. Explain how pioneer species modify the environment for later arrivals.
3. Critique the concept of a 'climax community' in light of ongoing environmental change.

Learning Objectives

• Compare and contrast primary and secondary ecological succession, identifying key differences in starting conditions and initial colonizers.
• Explain the role of pioneer species in facilitating the establishment of later successional species by altering environmental factors.
• Analyze case studies of ecological disturbances, such as Mount St. Helens or Yellowstone fires, to trace the stages of succession over time.
• Critique the traditional concept of a climax community by evaluating evidence of ongoing disturbance and ecosystem dynamism.

Before You Start

Basic Ecology: Biotic and Abiotic Factors

Why: Students need to understand the components of an ecosystem to grasp how changes in these factors drive succession.

Plant Adaptations

Why: Knowledge of how plants are adapted to different environments is crucial for understanding the success of pioneer species and later arrivals.

Key Vocabulary

Ecological Succession	The gradual process by which ecosystems change and develop over time, involving predictable shifts in species composition.
Primary Succession	Ecological change that begins on surfaces devoid of soil and life, such as newly formed volcanic rock or glacial till.
Secondary Succession	Ecological change that occurs in areas where a community previously existed but has been disturbed, leaving soil intact.
Pioneer Species	The first organisms, typically hardy plants like lichens and mosses, to colonize barren land and initiate ecological succession.
Climax Community	A theoretical stable, mature ecological community that represents the final stage of succession for a given environment.

Watch Out for These Misconceptions

Common Misconception

Succession always ends in a forest.

What to Teach Instead

The endpoint of succession depends entirely on regional climate. In grassland climates, succession ends in grassland; in arid regions, it ends in shrubland or desert. The climax community is the community most stable under prevailing climatic conditions, not always a forest. Examining photographs of climax communities from different US biomes helps correct this assumption effectively.

Common Misconception

Primary succession is faster than secondary succession.

What to Teach Instead

Secondary succession is almost always faster because the soil, seed bank, and sometimes root systems from the previous community remain intact. Primary succession on bare rock can take centuries or millennia. Comparing time scales for a lava field and an abandoned farm field side by side on a timeline during a collaborative activity helps students internalize this difference.

Common Misconception

Pioneer species destroy the habitat by making it unsuitable for themselves.

What to Teach Instead

Pioneer species do modify the environment in ways that benefit later-arriving species more than themselves, leading to their competitive replacement. But this is a gradual facilitated displacement, not destruction. Tracing the specific mechanism (soil enrichment through organic matter and nitrogen fixation, then competitive establishment by later species) during a case study helps students see succession as a series of facilitated replacements driven by soil development.

Active Learning Ideas

Photo Sequencing: Succession Timeline

Small groups receive 8 to 10 photographs taken at different times after a specific disturbance (Mount St. Helens volcano sites or Yellowstone post-1988 fire areas). Students arrange the photos in chronological order, justify the sequence using ecological logic, and label each photo with the dominant functional group and its role in facilitating the next stage.

40 min·Small Groups

Simulation Game: Succession Dice Game

Students represent different plant species with specific colonization, growth, and displacement rules encoded on cards. Each round, dice rolls determine whether each species establishes, grows, or is displaced. The class tracks community composition over 20 rounds, graphs the proportional representation of each species, and identifies the successional trajectory that emerges.

45 min·Small Groups

Collaborative Debate: Is the Climax Community Concept Accurate?

Students read two short competing passages: one presenting the classical climax community model and one presenting the modern non-equilibrium disturbance perspective. Small groups create a two-column evidence chart, then participate in a structured class discussion to develop a nuanced position on whether 'climax community' is a useful scientific concept.

40 min·Small Groups

Think-Pair-Share: Classifying Succession Types

Students receive six disturbance scenarios (volcanic eruption, forest fire, glacier retreat, agricultural abandonment, hurricane, quarry abandonment) and classify each as primary or secondary succession. They compare predictions with a partner, resolve differences by applying the soil criterion, and then predict the first three functional groups to colonize each site.

25 min·Pairs

Real-World Connections

• Restoration ecologists use their understanding of succession to guide the replanting and management of areas damaged by deforestation or mining, aiming to re-establish native plant and animal communities.
• Forestry professionals in fire-prone regions, like the Pacific Northwest, study secondary succession to predict forest recovery rates after wildfires and inform management strategies for timber resources and biodiversity.
• Park rangers at national parks, such as Yellowstone, monitor the effects of natural disturbances like fires and volcanic activity on ecosystem recovery, using succession principles to interpret landscape changes for visitors.

Assessment Ideas

Quick Check

Present students with two scenarios: one describing colonization of a new lava flow, the other an abandoned farm field. Ask students to write one sentence identifying which is primary succession and one sentence identifying which is secondary succession, and why.

Discussion Prompt

Pose the question: 'Is the idea of a permanent climax community still valid today?' Facilitate a class discussion where students cite examples of ongoing disturbances and ecosystem resilience to support their arguments.

Exit Ticket

Provide students with images depicting different stages of plant growth on a bare rock surface. Ask them to label the images in the correct order of primary succession and identify one pioneer species that might be present in the earliest stage.

Frequently Asked Questions

What is the difference between primary and secondary succession?

Primary succession begins on bare substrate where no soil exists, such as a newly cooled lava flow or an exposed glacial moraine. Secondary succession begins where an established community was disrupted but the soil remains, such as a field abandoned after farming or a forest recovering after a fire. Secondary succession is faster because it starts with existing soil nutrients and typically has surviving seeds or root systems already present.

How do pioneer species change the environment for later arrivals?

Pioneer species begin building soil by breaking rock through secretions (in the case of lichens) and adding organic matter as they die and decompose. This creates a gradually thickening layer of nutrient-containing soil that can support more demanding plants. Each successional stage modifies conditions in ways that favor the next stage over itself, driving the sequence of community replacement that defines succession.

What are the limitations of the climax community concept?

The climax community concept implies that succession reaches a stable, self-perpetuating endpoint. Modern ecology recognizes that most ecosystems are continuously disturbed at various spatial scales and that communities exist in dynamic flux. Many ecologically valuable communities, including fire-maintained grasslands and early-successional habitats for disturbance-dependent species, require ongoing disturbance to persist. The concept of a permanent stable climax oversimplifies a more dynamic ecological reality.

What active learning strategies work best for teaching ecological succession?

Photo sequencing activities are highly effective because they train students to use ecological reasoning to reconstruct a temporal process from visual evidence, a genuine scientific skill. When students must justify why one photo precedes another based on species composition and soil characteristics rather than a labeled diagram, they engage with succession mechanistically. Pairing this with the Climax Community Debate develops the additional capacity to evaluate contested scientific concepts using evidence.