What you need to know
- 5.15Stages of successionThe gradual change in the community of an area over time, as each set of species changes the conditions for the next. from colonisationThe arrival and establishment of a species in an area where it was not found before. to the formation of a climax communityThe stable community at the end of succession..
Climate-change shifts of range are 5C. Speciation is 5.23–5.24, also 5C. A named sere (hydrosere, lithosere) is useful language, not extra specification codes.
By the end, you should be able to…
- Outline colonisation, change through time and a climax community.
- Distinguish primary from secondary successionSuccession on ground that already has soil, after the previous community was removed, for example by fire..
- Explain how organisms alter abioticNon-living. Abiotic factors include light, temperature, water and soil pH. conditions for later speciesA group of organisms that can interbreed to produce fertile offspring..
Build your understanding
Colonisers change the ground
successionThe gradual change in the community of an area over time, as each set of species changes the conditions for the next. is the directional change of a communityAll the populations of different species living in one habitat at the same time. over time. It starts with colonisationThe arrival and establishment of a species in an area where it was not found before.: pioneer speciesThe first species to colonise bare ground, such as lichens. They begin to form soil. arrive on new or cleared ground. Pioneers often tolerate exposed abioticNon-living. Abiotic factors include light, temperature, water and soil pH. conditions — high light, little soil, poor water-holding — and they change those conditions by adding organic matter, reducing erosion, or providing shade.
primary successionSuccession starting on bare ground with no soil, such as bare rock or sand. starts where there is no previous soil: cooled lava, bare rock, a new sand bank. secondary successionSuccession on ground that already has soil, after the previous community was removed, for example by fire. starts where a community has been removed but soil remains: after felling, fire, or a severe flood. Secondary change is usually faster because seeds, roots and nutrients are already present.
A climax is more stable, not immortal
Later communities often include larger, longer-lived plants that create shade and a more structured habitatThe place where an organism lives.. A climax communityThe stable community at the end of succession. is the more stable mix that persists under the prevailing climate and soils if major disturbance stays away. “Stable” means speciesA group of organisms that can interbreed to produce fertile offspring. composition changes slowly, not that nothing dies.
Grazing, fire, storms and people can hold a community at an intermediate stage (a plagioclimax in some textbooks). That word is enrichment. The specification requires the idea of stages from colonisation to climax, not a claim that every site ends as oak woodland.
Biotic and abiotic travel together
Each stage alters light, soil water, mineral ions and shelter, so new species can establish and some pioneers are shaded out. Distribution of later species is therefore not independent of what lived there before. That is succession as an ecological process, not evolution of new species (5C).
A transectA line across a habitat along which samples are taken, to show how organisms change with conditions. from open sand to scrub can look like succession in space. It is supporting evidence only if you also have reasons to think the zones are stages in time, not just different soils that have always been different.
Follow the process
Bare or cleared ground → pioneer colonisers tolerate the harsh abiotic conditions → they add organic matter, shade or better water-holding → those changed conditions let later species establish, and some pioneers are shaded out → a climax community then changes only slowly if the climate and major disturbance stay the same. Primary succession has no previous soil. Secondary succession has soil left, so it is usually faster. This is a change of community, not the evolution of a new species.
NOT: succession is not animals turning into plants, and it is not the evolution of a new species.
- Primary succession: no previous soil, such as bare rock or cooled lava
- Secondary succession: soil remains, so change is usually faster
- A spatial zonation is evidence of time only if the soils were not always different
- Grazing or mowing can hold a community before the climax; that name is enrichment
- The climax depends on the prevailing climate, not on one named tree everywhere
Two traps this diagram blocks
- Do not describe succession as one species evolving into another.
- Do not say every site ends as the same woodland.
From the diagram alone
Question
Explain the difference between primary and secondary succession, and state what the pioneer stage does to the habitat. [4]
Show a model answer
Primary succession starts where there is no soil. Secondary succession starts where a community has been removed but soil remains, so it is usually faster. Pioneers change the abiotic conditions, for example by adding organic matter or shade, which lets later species establish.
| Primary | Secondary | |
|---|---|---|
| Starting surface | New rock, lava, sand with no soil | Cleared ground with soil remaining |
| Pioneers | Often lichens, algae or hardy plants that can make a soil start | Seed bank, roots and colonists from nearby |
| Speed | Usually slower | Usually faster |
Make your reasoning visible
Build the explanation
X happens because Y, leading to Z. X: later speciesA group of organisms that can interbreed to produce fertile offspring. replace the pioneers. Y: the pioneers change abioticNon-living. Abiotic factors include light, temperature, water and soil pH. conditions, for example by adding humus and shade. Z: the communityAll the populations of different species living in one habitat at the same time. moves towards a climax that is stable under that climate. Incomplete: “Plants grow and then there is a forest.” Improved: “pioneer speciesThe first species to colonise bare ground, such as lichens. They begin to form soil. colonise bare ground and change the soil and light, so later species can establish and a climax communityThe stable community at the end of succession. can persist.” The improvement names the change in conditions.
Name a change in conditions
“Pioneers make soil / shade / nitrogen” is stronger than “then bigger plants come”.
Climax is climate-dependent
A desert climax is not a rainforest. Do not write a single universal end-point.
Key explanations
- Some earlier species are then shaded out. This is replacement of populations, not evolution of a new species.
Avoid this misconception
The claim: successionThe gradual change in the community of an area over time, as each set of species changes the conditions for the next. is animals turning into plants, or new species evolving on the lava.
The correction: It is a change in which populations occupy the site. Evolution of new species is a different specification idea.
Order the stages of succession
In succession each community changes the conditions so that the next can grow. Order primary succession on bare rock.
Order the steps
What to do
- Reorder the cards below: drag a card (on a touch screen, drag its number), tap a card then tap where it goes, or use the ↑ and ↓ arrows at its right.
- Press Check under the cards to mark each one green (right place) or red; the count shows how many are right.
- Stuck? Hint first outlines the first wrong place, then gives a clue, then places that step for you.
- Shuffle mixes the cards again; Start again returns them to the starting order. Keyboard: Space picks up, arrow keys move, Space drops.
New bare rock is exposed. Put the stages of succession in order.
0 of 6 in the right place
Secondary succession starts from existing soil (for example after a fire), so it skips the pioneer stage. Human activity can hold a community before the climax (a plagioclimax).
Check your understanding
Try each question before opening the suggested answer.
Practice question
Retrieval and explanation · suggested answer
What is colonisation in succession?
Show suggested answer
The arrival and establishment of the first species, the pioneers, on new or cleared ground.
Practice question
Retrieval and explanation · suggested answer
Distinguish primary and secondary succession.
Show suggested answer
Primary starts without soil, on new surfaces. Secondary starts where soil and often a seed bank remain after disturbance.
Practice question
Retrieval and explanation · suggested answer
What is meant by a climax community?
Show suggested answer
A more stable community that persists under the prevailing conditions if not reset by major disturbance.
Take the idea further
Apply the same specification knowledge to an unfamiliar problem. Any extra assumptions are supplied in the question.
Stretch question
After a volcanic blast, some seeds and burrowing animals survive under debris while other ground is sterile. Which patches will more closely resemble secondary succession, and why might a single climax diagram be too simple?
Show a hint
Biological leftovers matter.
Explore the reasoning
Patches with surviving seeds, roots or animals already have a biological start, more like secondary succession. Sterile pumice is closer to primary. Different disturbance intensities therefore produce a mosaic, not one tidy sequence, so a single climax sketch is a model, not a map of every square metre.
Recall this lesson
Lesson recall questions
Question 1 of 5: Name the first organisms to colonise bare rock, and the term for them.
Succession to climax
Practice question
Retrieval and explanation · suggested answer
Name the first organisms to colonise bare rock, and the term for them.
Lesson: 5B 2: How Ecosystems Evolve
Try this from memory first.
Put your biology to work
Explore where these ideas appear in the world. Enrichment, not extra required recall.
Recovery is not a blank page
5B · How Ecosystems EvolveUSGS accounts of Mount St. Helens after 1980 describe surviving seeds, spores, gophers and fungi as well as later colonists such as prairie lupines. Aquatic systems often rebounded…Specification 5.15Read & use the scienceClose article
Why this matters
USGS accounts of Mount St. Helens after 1980 describe surviving seeds, spores, gophers and fungi as well as later colonists such as prairie lupines. Aquatic systems often rebounded faster than forests. That research is enrichment: it shows succession as a real, messy process with biological leftovers, not a cartoon that always starts from nothing. That makes the initial conditions important. A surviving soil layer can supply nutrients, microbes and dormant seeds, so two patches of the same mountain may follow very different sequences after the same eruption.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 4, pp. 29–32. The application extends beyond required recall.
- 5.15 understand the stages of succession from colonisation to the formation of a climax community
Use the science
Why does a surviving seed bank make “primary succession on the whole mountain” an over-simple headline?
Explore a possible response
Where soil and seeds remained, change was closer to secondary succession. Only fully new, sterile surfaces behaved like a true primary start.
Explore the source
- USGS: ecology of Mount St. Helens National MonumentU.S. Geological Survey
A buried forest waiting for disturbance
5B · How Ecosystems EvolveUS Forest Service researchers describe the soil seed bank as a hidden reserve of living seeds that can survive a disturbance. Fire, browsing by deer and gaps in…Specification 5.15Read & use the scienceClose article
Why this matters
US Forest Service researchers describe the soil seed bank as a hidden reserve of living seeds that can survive a disturbance. Fire, browsing by deer and gaps in the canopy change which plants return. The first visible seedlings do not necessarily arrive from outside; some were already below ground. That complicates the simple school succession diagram in a useful way. Where soil and a seed bank remain, recovery resembles secondary succession, with a biological legacy from the previous community. A site stripped to new bare rock has a very different starting point and may need pioneers to build soil first.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 4, pp. 29–32. The application extends beyond required recall.
- 5.15 understand the stages of succession from colonisation to the formation of a climax community
Use the science
Why might two burned forest patches develop different plant communities even if they receive the same rainfall afterward?
Explore a possible response
They may have different surviving seed banks, soil, browsing pressure and light after the fire. Initial biological legacies alter the sequence.
Explore the source
- How fire, deer and canopy gaps shape seed banksUS Forest Service