Science · Grade 7 · Interactions within Ecosystems · Term 1

Ecological Succession: Primary and Secondary

Investigating how ecosystems change over time, from primary succession to climax communities.

• Ontario Curriculum Expectations
• MS-LS2-4

About This Topic

Ecological succession traces how ecosystems develop and change over time after disturbances. Primary succession starts on bare rock or lava, where pioneer species such as lichens and mosses break down rock to form soil, paving the way for grasses, shrubs, and trees until a stable climax community forms. Secondary succession occurs faster in areas with existing soil, like after forest fires or floods, beginning with fast-growing herbs and progressing through similar stages to a climax community.

This topic anchors the Interactions within Ecosystems unit by showing how species interactions drive community assembly and biodiversity. Students differentiate the two types, examine pioneer species roles in soil formation and nutrient cycling, and predict changes after events like wildfires, aligning with standards on population dynamics and ecosystem resilience.

Active learning suits this topic well. Succession unfolds over decades or centuries, yet students model it quickly through layered terrariums or timeline constructions. These hands-on methods make long-term processes visible, foster prediction skills, and connect abstract ideas to local examples like abandoned fields.

Key Questions

1. Differentiate between primary and secondary succession with examples.
2. Analyze the role of pioneer species in establishing new ecosystems.
3. Predict the sequence of changes in an ecosystem after a major natural disaster.

Learning Objectives

• Compare and contrast the initial conditions and processes involved in primary and secondary ecological succession.
• Analyze the role of pioneer species in soil formation and the establishment of new plant communities.
• Predict the sequence of plant and animal community changes following a significant natural disturbance, such as a volcanic eruption or a forest fire.
• Classify different stages of ecological succession based on the dominant plant species present.

Before You Start

Introduction to Ecosystems

Why: Students need a basic understanding of what an ecosystem is, including biotic and abiotic factors, before learning how they change over time.

Food Chains and Food Webs

Why: Understanding how energy flows through an ecosystem is foundational to comprehending how different species interact and change during succession.

Key Vocabulary

Ecological Succession	The gradual process by which ecosystems change and develop over time, leading to a more stable climax community.
Primary Succession	Ecological change that begins on surfaces that are devoid of soil, such as bare rock, lava flows, or sand dunes.
Secondary Succession	Ecological change that occurs in areas where a previous community existed but was disturbed, leaving soil intact, such as after a fire or logging.
Pioneer Species	The first species, typically hardy plants like lichens and mosses, to colonize barren land and initiate soil formation.
Climax Community	A stable, mature ecological community that represents the final stage of succession for a particular environment.

Watch Out for These Misconceptions

Common Misconception

Primary and secondary succession happen at the same speed.

What to Teach Instead

Primary takes centuries due to soil building, while secondary uses existing soil for quicker regrowth. Hands-on terrarium comparisons let students time both processes side-by-side, revealing speed differences through direct observation and measurement.

Common Misconception

Succession always reaches the exact same climax community.

What to Teach Instead

Climax depends on climate and soil; disturbances can restart cycles. Group timeline debates expose variations, as students defend predictions with local examples and adjust models collaboratively.

Common Misconception

Pioneer species disappear once succession advances.

What to Teach Instead

Pioneers create conditions for others but may persist marginally. Succession station rotations help students track species persistence in models, challenging the idea through repeated observations.

Active Learning Ideas

Stations Rotation: Succession Stages

Prepare four stations with trays: bare rock (lichens simulated by moss), soil formation (add grasses), shrub stage (plant small bushes), and climax forest (add trees). Groups rotate every 10 minutes, sketching changes and noting pioneer roles. Conclude with a class chart comparing primary to secondary.

45 min·Small Groups

Timeline Construction: Predict Post-Fire Recovery

Provide images of a burned forest area over years. In pairs, students sequence cards showing grasses, shrubs, and trees into a timeline, labeling pioneer species and soil advantages. They predict year 50 based on patterns.

30 min·Pairs

Microcosm Model: Build Your Ecosystem

Students layer jars: primary with rock and lichens, secondary with soil and seeds. Observe weekly over two weeks, recording species arrival and changes. Discuss acceleration in secondary setups.

40 min·Individual

Case Study Debate: Local Disturbance

Share a real Ontario forest fire case. Groups debate primary vs. secondary paths, citing evidence from photos. Vote on predictions for biodiversity recovery.

35 min·Small Groups

Real-World Connections

• Ecologists study the succession of plant life on Mount St. Helens after its 1980 eruption to understand how ecosystems recover from catastrophic events.
• Forestry managers use knowledge of secondary succession to plan reforestation efforts after wildfires, predicting which tree species will naturally colonize the area first.
• Restoration ecologists apply principles of succession when rehabilitating degraded lands, such as abandoned mine sites, by introducing appropriate pioneer species to kickstart soil development.

Assessment Ideas

Quick Check

Present students with images of different landscapes (e.g., bare rock, a recently burned forest, a mature forest). Ask them to label each image as representing primary succession, secondary succession, or a climax community, and briefly explain their reasoning.

Exit Ticket

On an index card, have students define primary succession in their own words and provide one example of a pioneer species. Then, ask them to define secondary succession and give an example of a disturbance that would lead to it.

Discussion Prompt

Pose the question: 'Imagine a large area of forest is cleared for a new housing development. What types of plants do you predict will be the first to grow back in the cleared areas, and why? What might the ecosystem look like in 50 years?' Facilitate a class discussion on their predictions.

Frequently Asked Questions

How do I differentiate primary and secondary succession for grade 7?

Use visuals: primary on bare surfaces like moraines, secondary after fires on soil-rich ground. Anchor with Ontario examples, such as Niagara Escarpment lichens versus post-logging fields. Build models to show soil's role in speeding secondary stages, reinforcing through prediction tasks.

What are pioneer species and their role in succession?

Pioneer species, like lichens or grasses, tolerate harsh conditions, fix nitrogen, and build soil. They enable later species arrival. Students investigate via microcosms, observing how pioneers alter habitats for biodiversity gains over simulated time.

How can active learning help teach ecological succession?

Active methods compress time scales: terrariums show weekly changes mimicking decades, while station rotations let groups experience pioneer-to-climax shifts. Predictions from disaster scenarios build systems thinking. Collaborative charting connects observations to Ontario ecosystems, making abstract concepts concrete and memorable for all learners.

What examples of succession fit Ontario curriculum?

Primary: Great Lakes sand dunes with grasses to forests. Secondary: Algonquin Park fires, regrowing from soil seeds. Use local photos and data logs for predictions, tying to climate resilience and tying into unit questions on interactions.