Year 11 Biology Module 4 · IQ3 Lesson 15 of 18 ~35 min

Ecological Succession — Primary, Secondary and Climax Communities

In the summer of 2019–20, the Black Summer fires burned 24 million hectares of Australia — an area the size of the United Kingdom. Temperate forests that had stood for centuries were reduced to ash. But beneath the blackened trunks, something was already happening. Seeds dormant for decades burst open. Epicormic buds beneath charred bark sprouted green shoots. Within weeks, the forest began rebuilding itself. This is ecological succession — nature’s process of recovery and rebirth.

🔥

Printable worksheet

Download this lesson's worksheet

Use the PDF for classwork, homework or revision. It includes key ideas, activities, questions, an extend task and success-criteria proof.

Download PDF Open printable version

Think First

Before you read, commit to a prediction. You will revisit these at the end.

Q1. The Black Summer fires burned a eucalyptus forest to the ground. The soil is still present, but all above-ground vegetation is gone. Predict what you would see if you visited the same spot in 6 months, 5 years, and 50 years. What species would appear first, and what would the final community look like?

Q2. A volcanic eruption creates a new island of bare lava rock with no soil. Predict how this island would differ in its recovery trajectory compared to the burned forest. Which would recover faster, and why?

What is Ecological Succession?

Ecological succession is the directional, predictable process of community change over time on a site. A disturbed or newly formed habitat is colonised by a sequence of species, each modifying the environment for the next, until a relatively stable climax community is reached.

Primary vs secondary succession

🗼 Primary Succession

Starts from: Bare substrate with no soil

Examples: New volcanic lava, recently exposed glacial till, bare sand dunes, freshly deposited river silt

Speed: Very slow — soil must form from scratch

First colonisers: Pioneer species such as lichens, nitrogen-fixing bacteria, and specialised grasses

Key process: Facilitation — early species modify the environment (add organic matter, fix nitrogen, stabilise substrate) making it suitable for later species

🔥 Secondary Succession

Starts from: Previously vegetated land where soil remains intact

Examples: After fire, flood, logging, cyclone damage, agricultural abandonment

Speed: Faster — seed bank persists, soil nutrients and structure are intact, roots may resprout

First colonisers: Fire ephemerals, resprouting shrubs, fast-growing herbs from soil seed bank

Key process: Release from suppression — disturbance removes dominant competitors, allowing suppressed species to germinate and grow

⚠️

Most common exam error: Students confuse primary and secondary succession. Remember: primary = no soil. If soil exists, it is secondary. A forest after fire has soil — it is secondary. A lava flow has no soil — it is primary. This distinction is worth marks in almost every HSC succession question.

Primary Succession — Building from Nothing

Primary succession is the ultimate test of life’s resilience. On bare rock or sand, there is no soil, no organic matter, no nitrogen. The first colonisers must tolerate extreme conditions and, crucially, must modify those conditions so that other species can follow.

Stages of primary succession: Australian sand dunes

Pioneer stage

Spinifex grass and marram grass colonise bare sand. Their deep, extensive root systems stabilise shifting dunes and trap wind-blown sand. As plants die, organic matter begins to accumulate. Nitrogen-fixing bacteria associated with grass roots add usable nitrogen to the sand.

Early succession

Mosses and small herbs colonise the stabilised sand. Soil begins to form as organic matter mixes with mineral particles. Nitrogen content increases, moisture retention improves, and the surface becomes less hostile to seedling establishment.

Mid succession

Shrubs such as coastal banksia and wattle establish. Deeper roots improve soil structure and drainage. Increased shade changes the microclimate, creating cooler, moister conditions beneath the canopy. Shade-tolerant species begin to arrive.

Late succession

Tall trees such as smooth-barked apple and blackbutt form a woodland canopy. The canopy shades out earlier colonisers. Biodiversity peaks in the transition zones (ecotones) between open and closed canopy.

Climax community

A self-sustaining forest in equilibrium with the regional climate. On the NSW coast, this is typically coastal sclerophyll forest or rainforest depending on rainfall. The community is stable until the next major disturbance resets the cycle.

💡

Facilitation is the key: Early species do not just survive harsh conditions — they actively improve them. Without spinifex stabilising sand and adding organic matter, banksias and wattles could not establish. Without banksias shading the ground, forest trees would desiccate. Each stage makes the next possible. This is the essence of succession.

Secondary Succession — Recovery After Fire

Australian ecosystems are fire-adapted. Eucalypts have epicormic buds beneath their bark. Banksias hold seeds in woody cones that open only when heated. The soil seed bank contains fire ephemerals that have waited decades for their moment. When fire clears the canopy, these adaptations ensure rapid recovery.

Stages of secondary succession: Post-fire eucalyptus woodland

Immediate (days to weeks)

Ash covers the ground. Soil nutrients are temporarily elevated because fire releases minerals bound in plant tissue. The blackened landscape looks lifeless, but below ground, root systems remain alive.

Short term (weeks to months)

Fire ephemerals — annual herbs such as Brachyscome and Podolepis — germinate from the soil seed bank. Epicormic shoots sprout from the trunks and branches of surviving eucalypts. Lignotubers (swollen root bases) resprout in many understorey species.

Medium term (1–5 years)

The shrub layer re-establishes from resprouts and seed. Grass cover returns. Legumes such as pea bushes add nitrogen to the recovering soil. Insect populations rebound, followed by insectivorous birds and reptiles.

Long term (5–20 years)

The tree canopy closes. Shrub diversity peaks as light conditions transition from open to shaded. The understorey shifts from sun-loving pioneers to shade-tolerant species. Ground cover stabilises and soil erosion declines.

Maturity (20–150+ years)

The mature canopy is fully re-established. However, hollow-dependent species — possums, owls, parrots, bats — require tree hollows that take 80–150 years to form. Until then, these species cannot fully recolonise. The community is not truly “recovered” until hollow-bearing trees return.

🇦🇺

The Black Summer legacy: The 2019–20 fires burned with unprecedented intensity, killing even fire-adapted species in some areas. In the NSW South Coast forests, ecologists observed that while eucalypts resprouted as expected, the intensity of the fires meant that some seed banks were incinerated. Recovery in these patches may take longer than historical norms, and the final community may differ from the pre-fire state. Climate change is making fires hotter and more frequent, potentially pushing some ecosystems past their resilience threshold.

Key Concepts in Succession

Beyond the stages, several underlying processes and principles determine how succession unfolds. Understanding these separates a Band 4 response from a Band 6 response.

Facilitation

Early species modify the environment in ways that benefit later species. Pioneer species do not simply tolerate harsh conditions — they improve them. This is the dominant mechanism in primary succession.

Example: Legumes fix atmospheric nitrogen into forms usable by other plants. When they die and decompose, this nitrogen enriches the soil for subsequent colonisers.

Inhibition

Early species modify the environment in ways that prevent other species from establishing. They monopolise space, light, or nutrients.

Example: Dense spinifex cover on dunes can prevent shrub seedlings from establishing until the grass clumps die back or are disturbed.

Tolerance

Later species are simply better competitors under the conditions created by earlier species. They do not need early species to prepare the ground; they can tolerate the conditions once they arise.

Example: Shade-tolerant forest tree seedlings can survive in the understorey of a developing woodland, waiting for a canopy gap to reach the light.

Climax community

A relatively stable community in equilibrium with regional climate and soil. It is self-sustaining and persists until the next major disturbance. The climax community is determined by climate, not by the starting conditions.

Example: The same starting substrate (sand dune) will climax as rainforest in high-rainfall Queensland but as sclerophyll woodland in drier NSW.

💡

Modern view: The concept of a single, stable climax community has been challenged. Many ecologists now view succession as a shifting mosaic where patches are at different stages, and disturbance is a constant rather than an exception. In fire-prone Australia, the “climax” is better understood as a fire-maintained equilibrium — the community persists because fire returns before late-successional species can dominate.

Activity: Sequence and Order

Test your understanding of succession by sequencing stages and matching concepts.

Part A — Sequence the Stages

The following stages describe secondary succession after a bushfire in a eucalyptus woodland. Write the correct order (1–5) in the space provided.

__ Tree canopy closes; shrub diversity peaks as light transitions from open to shaded.

__ Ash covers the ground; soil nutrients are temporarily elevated from burned plant material.

__ Mature canopy re-established; hollow-dependent species begin to return as tree hollows form.

__ Fire ephemerals germinate from soil seed bank; epicormic shoots sprout from eucalypt trunks.

__ Shrub layer re-establishes; grass cover returns; legumes add nitrogen to recovering soil.

Correct order: 4, 1, 5, 2, 3

Part B — Predict and Explain

A new sand dune forms on the coast of Victoria after a storm. Describe the first three stages of primary succession on this dune. For each stage, name a likely pioneer species and explain how it modifies the environment for the next stage. (6 marks)

Copy Into Your Books

Definition

Ecological succession: A directional, predictable process of community change over time on a site, developing through sequential stages toward a stable climax community.

Primary succession

Starts from bare substrate with no soil. Very slow (decades to centuries). Pioneer species (lichens, grasses) modify the environment through facilitation. Australian example: coastal sand dune succession.

Secondary succession

Starts from previously vegetated land with soil intact. Faster because seed bank persists and roots may resprout. Australian example: post-fire eucalyptus woodland recovery.

Key concept: facilitation

Early species modify the environment (add organic matter, fix nitrogen, stabilise soil) making conditions suitable for later species that could not have colonised bare substrate directly.

Australian fire adaptations

Eucalypts have epicormic buds beneath bark for resprouting. Banksias hold seeds in fire-opened cones. Soil seed banks contain fire ephemerals waiting for disturbance.

Syllabus link

ACSBL050, ACSBL053, ACSBL060: Predict how disturbance affects species distribution and abundance over time; distinguish primary from secondary succession.

Revisit Your Predictions

Now that you have completed the lesson, review your initial answers. What did you get right? What surprised you?

Lesson Summary

In this lesson you learned:

Ecological succession is the directional, predictable process of community change over time toward a stable climax community.
Primary succession starts from bare substrate with no soil. It is very slow because soil must form from scratch. Pioneer species facilitate later colonisation by modifying the environment.
Secondary succession occurs on previously vegetated land where soil remains intact. It is faster because seed banks persist and roots may resprout.
The Australian sand dune example shows primary succession: spinifex stabilises sand → mosses and herbs form soil → shrubs establish → woodland develops → climax forest.
The Australian post-fire eucalyptus woodland shows secondary succession: ash and nutrients → fire ephemerals and resprouts → shrub recovery → canopy closure → mature forest with hollow-bearing trees.
Facilitation is the key process in primary succession — early species make conditions suitable for later species. Inhibition and tolerance also operate at different stages.
The climax community is determined by regional climate, not starting conditions. In fire-prone Australia, the climax is often a fire-maintained equilibrium.

I have completed this lesson and copied the key points into my notes.

Practice Questions

Test your understanding of ecological succession

Q1. Which of the following best distinguishes primary succession from secondary succession?

A Primary succession occurs only on land, while secondary succession occurs only in water

B Primary succession begins on bare substrate with no soil; secondary succession begins where soil remains intact

C Primary succession is faster than secondary succession because there is no competition

D Primary succession produces more biodiversity than secondary succession

Q2. What is the primary role of pioneer species in primary succession?

A To outcompete all other species and dominate the climax community

B To prevent later species from establishing by monopolising resources

C To modify the environment through facilitation, making conditions suitable for later colonisers

D To consume decomposers and recycle nutrients back to the soil

Q3. Why does secondary succession generally proceed faster than primary succession?

A Soil structure, nutrients, and seed banks are already present

B Pioneer species in secondary succession reproduce more quickly

C Secondary succession receives more rainfall than primary succession

D There is less competition in secondary succession

Q4. Eucalyptus trees resprouting from epicormic buds beneath their bark after a bushfire is an example of:

A Primary succession on bare rock

B Facilitation by a pioneer species

C The enemy release hypothesis

D A fire adaptation that accelerates secondary succession

Q5. A climax community is best defined as:

A The first community to colonise a disturbed site

B A self-sustaining community in equilibrium with the prevailing climate

C A community with the highest possible biodiversity

D A community that never experiences disturbance

Short Answer

Q1. Distinguish between primary and secondary succession. In your answer, define each type and provide one named Australian example for each. (4 marks)

Q2. Explain the role of facilitation in primary succession. Use the Australian coastal sand dune example to illustrate how pioneer species modify the environment for later colonisers. (4 marks)

Q3. The 2019–20 Black Summer fires burned a eucalyptus forest in southern NSW. The soil remained intact, but all above-ground vegetation was destroyed.

(a) Predict what the community would look like 6 months after the fire. Name at least two species or groups you would expect to see and explain their appearance. (2 marks)

(b) Predict what the community would look like 5 years after the fire. Describe changes in vegetation structure and explain why these changes occur. (2 marks)

(c) Predict what the community would look like 50 years after the fire. Explain why some species may still not have returned, even after half a century. (2 marks)

Comprehensive Answers

Primary succession occurs on bare substrate where no soil exists. Pioneer species such as lichens and specialised grasses must colonise raw rock or sand and begin soil formation. It is very slow, taking decades to centuries, because organic matter must accumulate and soil structure must develop from scratch (1 mark). Australian example: coastal sand dune succession where spinifex grass colonises bare sand and gradually builds soil for shrub and tree establishment (1 mark).

Secondary succession occurs on previously vegetated land where soil remains intact after a disturbance such as fire, flood, or logging (1 mark). It proceeds faster than primary succession because seed banks persist in the soil, nutrients are already present, and many plants can resprout from surviving root systems. Australian example: post-fire recovery in eucalyptus woodland, where epicormic shoots and soil-stored seeds allow rapid regeneration (1 mark).

Facilitation is the process by which early successional species modify the environment in ways that benefit later species, making conditions suitable for colonisers that could not have survived on the bare substrate directly (1 mark).

On Australian coastal sand dunes, spinifex grass and marram grass are pioneer species. Their deep, extensive root systems stabilise shifting sand and trap wind-blown particles, preventing erosion and building dune height (1 mark). As these grasses die and decompose, they add organic matter to the sand, beginning soil formation. Nitrogen-fixing bacteria associated with grass roots add usable nitrogen, enriching the nutrient-poor sand (1 mark).

These modifications create conditions suitable for mosses and small herbs, which require some soil moisture and organic content. Later, coastal banksia and wattle shrubs establish, their deeper roots further improving soil structure. Without the pioneer grasses preparing the ground, none of these later species could have colonised bare sand (1 mark).

(a) Six months after the fire, fire ephemerals such as Brachyscome daisies would germinate from the soil seed bank, taking advantage of elevated nutrients and reduced competition (1 mark). Eucalyptus trees would produce epicormic shoots from buds beneath their charred bark, and understorey species with lignotubers would resprout from their root bases (1 mark).

(b) After five years, the shrub layer would be well re-established from resprouts and seed. Grass cover would have returned, and legumes such as pea bushes would be adding nitrogen to the recovering soil (1 mark). The tree canopy would be beginning to close, changing light conditions in the understorey from open to shaded, which favours shade-tolerant species over sun-loving pioneers (1 mark).

(c) After 50 years, the mature canopy would be re-established and the community would resemble the pre-fire forest in structure. However, hollow-dependent species such as possums, owls, and parrots may still not have returned because tree hollows take 80–150 years to form naturally (1 mark). Without hollow-bearing trees, these species lack nesting and shelter sites, so the community is not fully recovered even after five decades (1 mark).