Science · 6th Grade · Energy Flow in Ecosystems · Weeks 19-27

Ecosystem Stability and Disturbances

Students evaluate how ecosystems respond to changes such as natural disasters or human intervention.

• Common Core State Standards
• MS-LS2-1
• MS-LS2-4

About This Topic

Ecosystems are not static systems but dynamic ones that constantly respond to disturbances ranging from wildfires and floods to invasive species and habitat fragmentation. This topic asks students to distinguish between two types of ecological response: resistance (the ability to withstand disturbance without changing) and resilience (the ability to recover after a disturbance). An old-growth forest may be resistant to a single dry season; a grassland that burned severely may show high resilience, recovering within a few years. This aligns with MS-LS2-1 and MS-LS2-4.

Students explore what makes some ecosystems more stable than others, including biodiversity, redundancy of function, and the presence of keystone species. Case studies like the Yellowstone fire recovery, coral bleaching events, or post-invasive species recovery in US ecosystems give students concrete examples to analyze.

This topic benefits from case-study based active learning because stability is an emergent property that must be understood through multiple interacting factors. Analyzing real ecosystems requires the kind of higher-order synthesis that collaborative investigation naturally promotes.

Key Questions

1. Explain how ecosystems recover after a major forest fire.
2. Differentiate between resistance and resilience in an ecosystem.
3. Analyze the factors that make some ecosystems more stable than others during a drought.

Learning Objectives

• Analyze case studies to explain how specific US ecosystems recover after a major disturbance, such as a forest fire or drought.
• Compare and contrast the concepts of ecosystem resistance and resilience using examples of different habitats.
• Evaluate the factors, including biodiversity and keystone species, that contribute to the stability of US ecosystems during periods of drought.
• Synthesize information from scientific articles to propose strategies for enhancing ecosystem resilience in the face of climate change.

Before You Start

Food Webs and Energy Transfer

Why: Students need to understand how energy flows through an ecosystem to grasp how disturbances disrupt these flows and impact stability.

Biotic and Abiotic Factors

Why: Understanding the components of an ecosystem is essential for analyzing how these factors are affected by and contribute to stability and disturbances.

Key Vocabulary

Ecosystem Disturbance	An event that disrupts the structure of an ecological community, such as a wildfire, flood, or human development.
Ecosystem Resistance	The ability of an ecosystem to remain relatively unchanged and maintain its structure and function when faced with a disturbance.
Ecosystem Resilience	The ability of an ecosystem to recover and return to its original state or a similar state after experiencing a disturbance.
Biodiversity	The variety of life within a particular habitat or ecosystem, including the diversity of species, genes, and ecosystems.
Keystone Species	A species that has a disproportionately large effect on its environment relative to its abundance, playing a critical role in maintaining ecosystem structure.

Watch Out for These Misconceptions

Common Misconception

Students often think that after a fire or storm, an ecosystem 'starts over' from zero and recovers in a predictable sequence back to its original state.

What to Teach Instead

Ecological succession after disturbance is real but rarely returns to the exact prior state. Factors like seed banks, soil conditions, and climate can produce different successional endpoints. The Yellowstone fire recovery is a good case because the regrown forest has a different species composition than the pre-fire forest, challenging the 'reset to default' assumption.

Common Misconception

Many students assume larger ecosystems are always more stable than smaller ones.

What to Teach Instead

Ecosystem size matters less than biodiversity and functional redundancy. A large monoculture is highly vulnerable to a single pest or disease. A small diverse wetland may recover from drought much faster than an adjacent irrigated cornfield. The drought comparison activity directly tests this assumption with evidence.

Common Misconception

Students sometimes think human activities that disturb ecosystems can simply be 'cleaned up' and the ecosystem will fully return to its previous state.

What to Teach Instead

Some disturbances cause regime shifts, tipping the ecosystem into an alternative stable state from which recovery is extremely difficult. Coral reef bleaching that exceeds a thermal threshold or the eutrophication of a shallow lake are examples where the original state may not be recoverable on human timescales. This is a sobering but important concept for environmental literacy.

Active Learning Ideas

Case Study Comparison: Fire Recovery vs. Invasive Species

Assign half the class to research the Yellowstone fire recovery (1988-present) and the other half to research a local or regional invasive species impact. Each group identifies whether the ecosystem showed resistance, resilience, or neither, and the factors that influenced the outcome. Groups present to each other and the class synthesizes a list of factors that promote ecosystem stability.

45 min·Small Groups

Simulation Game: Stability Jenga

Use a block tower where each block is labeled with a species or function in an ecosystem. Students take turns removing blocks (simulating species loss or disturbance) while the class predicts at each step whether the ecosystem can remain stable. After the tower falls, discuss which removals were most destabilizing and what that reveals about keystone species and functional redundancy.

25 min·Small Groups

Think-Pair-Share: Drought Resilience

Present data from two ecosystems facing the same drought: a monoculture cornfield and a tallgrass prairie. Pairs analyze which is more resilient and explain why, using evidence about biodiversity, root depth, soil structure, and species interactions. Pairs share their reasoning, and the class builds a conceptual model of what structural features predict resilience.

20 min·Pairs

Real-World Connections

• Ecologists with the National Park Service study the recovery of ecosystems after wildfires, like those in Yellowstone National Park, to inform land management and restoration efforts.
• Conservation scientists assess the resilience of coral reefs in Florida to rising ocean temperatures and acidification, developing strategies to protect these vital marine habitats.
• Forestry managers in the Pacific Northwest use data on tree species and soil conditions to predict how different forest types will respond to drought and to plan for sustainable timber harvesting.

Assessment Ideas

Exit Ticket

Provide students with a brief description of a hypothetical US ecosystem facing a specific disturbance (e.g., a coastal wetland after a hurricane). Ask them to write one sentence defining resistance and one sentence defining resilience in this context, and then predict which concept might be more important for the wetland's long-term survival.

Quick Check

Present students with two short case studies of US ecosystems recovering from disturbances. Ask them to identify one factor that promoted resistance in the first ecosystem and one factor that promoted resilience in the second ecosystem, writing their answers in their notebooks.

Discussion Prompt

Pose the question: 'Imagine a forest ecosystem that is highly resistant to small, frequent fires but takes a very long time to recover from a single, massive wildfire. Is this ecosystem more resistant or more resilient?' Facilitate a class discussion where students justify their answers using the vocabulary terms.

Frequently Asked Questions

How do ecosystems recover after a major forest fire?

Fire recovery begins within weeks as pioneer species, typically fast-growing grasses and shrubs, colonize the burned area. Over years to decades, taller shrubs and then trees return through ecological succession. Soil nutrients released by the fire initially promote rapid growth. Recovery speed depends on fire intensity, soil health, seed availability, climate, and whether nearby intact habitat provides a source of colonizing species.

What is the difference between resistance and resilience in an ecosystem?

Resistance is an ecosystem's ability to withstand a disturbance with little or no change. A mature rainforest may resist a single drought with minimal change because of its deep soil moisture. Resilience is the ability to recover after a disturbance does cause change. A grassland that burns and regrows within two years has high resilience. Both properties are important, and different ecosystems may be high in one but not the other.

What makes some ecosystems more stable than others during a drought or disturbance?

Higher biodiversity generally increases stability because more species means more functional redundancy: if one species declines, others with similar ecological roles can compensate. Ecosystems with deep-rooted plants, complex soil food webs, and diverse microbial communities tend to withstand drought better. Keystone species also play outsized roles, so ecosystems containing them are more buffered against cascading losses.

How does active learning help students understand ecosystem stability?

Stability is an emergent property shaped by many interacting factors, which makes it hard to grasp from a definition alone. Analyzing real case studies requires students to weigh evidence, identify causal factors, and draw conclusions, the same process ecologists use. The Stability Jenga simulation makes the role of redundancy and keystone species viscerally clear in a way that no textbook illustration can replicate.