D4.2.13 (HL)—Changes during primary succession
Primary succession gradually changes bare surfaces into more complex communities as pioneers form soil, increase biomass, and support food webs.
- Syllabus
- First assessment 2025
- Objective
- D4.2.13
- Level
- HL
Exam analysis
Chance of appearing4%of analysed past papers
Latest appearanceNovember 2025
Most common paperPaper3
Typical marks1–2
Common command terms
- Describe
- Explain
- Suggest
- State
- Outline
- Predict
Scoring notes
- Common mistake
- Forgetting that primary succession begins on bare substrate with little or no soil.
Recent exam appearances
November 2025Paper1A ["HL"] · TZ139[ 1 ]D4.2.13 (HL)—Changes during primary succession
May 2025Paper1A ["HL"] · TZ139[ 1 ]D4.2.13 (HL)—Changes during primary succession
May 2018Paper3 ["HL"] · TZ115(b)[ 3 ]D4.2.13 (HL)—Changes during primary succession
May 2015Paper3 ["HL"] · TZ111(b)(i)[ 1 ]D4.2.13 (HL)—Changes during primary succession
November 2014Paper3 ["HL"] · TZ011(c)[ 2 ]D4.2.13 (HL)—Changes during primary succession
Practice this objective
Coverage 2014–2025 · Updated 16 Jul 2026
Primary Succession Begins without Developed Soil
HL onlyPrimary succession starts on a surface lacking soil and usually proceeds through colonization, soil formation and increasing structural complexity.
Pioneer organisms weather substrate and add organic matter; later plants deepen soil and change resources. The process is slow because soil must develop.
Check whether soil and a biological legacy remain before calling a sequence primary.; separate state, pressure, control loop and time
Lichens colonize fresh volcanic rock, add organic matter, and help later mosses and vascular plants establish. This gives a concrete prediction from the stated ecosystem.
A cleared field with existing soil is secondary succession, even if most vegetation was removed. Interpret the result within the stated model and evidence limits.
Changes during primary succession
HL onlyAssessment in practice
1–3 marksHow it is assessed
This objective is assessed through structured response, commonly using Describe / Explain / Suggest.
Command terms
Describe / Explain / Suggest / State / Outline / Predict
What earns marks
Build the answer around this relationship: Pioneer organisms colonize bare surfaces and begin changing the abiotic environment.
Watch for
Forgetting that primary succession begins on bare substrate with little or no soil.
Representative question
Question 1
Outline the ecological changes that will occur on the island of cooled lava.
Retrieve the HL Succession Route
HL onlyHL D4.2 is the long-term change story. Succession begins after new habitat or disturbance, pioneer species modify conditions, primary succession builds soil and complexity, and some systems repeat cycles or are held before climax by disturbance.
- new habitat or disturbance opens space for community change
- bare surfaces gain soil, biomass, diversity, food webs, and nutrient cycling
- recurring disturbance or interactions repeat community changes
- local stable climax differs from disturbance-maintained earlier stages
HL Succession and Long-Term Change
HL onlyHL succession questions focus on community pathways over time. The answer starts from the initial condition, shows how species modify abiotic conditions and interactions, and identifies whether the pathway is primary, cyclical, climax, or arrested by repeated disturbance.
- Explain succession as community change over time after new habitat or disturbance.
- Use primary succession features: bare surface, soil formation, increasing biomass, diversity, food-web complexity, and nutrient cycling.
- Distinguish cyclical succession, climax communities, and arrested succession using the cause of repeated or stopped change.
Concept essentials
- Pioneer organisms colonize bare surfaces and begin changing the abiotic environment.
- Decomposition and weathering increase soil depth, organic matter, nutrients, and water retention.
- As primary succession proceeds, biomass, diversity, productivity, and food-web complexity usually increase.