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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 Builds Soil and Ecosystem Complexity

HL only

Primary succession begins on a surface without developed soil, so pioneer organisms must help create the conditions needed by later communities.

From pioneer to later stages General change
Plant size and biomass Increase
Amount of primary production Increase as producer cover develops
Species diversity Increase as more niches form
Food-web complexity Increase as trophic interactions accumulate
Nutrient cycling Becomes larger and more internally recycled as soil and biomass develop

On fresh volcanic rock, lichens and mosses weather substrate and add organic matter; deeper soil later supports herbs, shrubs and trees.

If soil and a biological legacy remain after disturbance, recovery is secondary rather than primary succession.

Changes during primary succession

HL only

Assessment in practice

1–3 marks
How 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

[Maximum number: 4]

Outline the ecological changes that will occur on the island of cooled lava.

Retrieve the HL Succession Route

HL only

HL 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 only

HL 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.