📌Definition Table

Term	Definition
Succession	The gradual change in community composition over time.
Primary succession	Succession starting on bare rock or newly formed surfaces with no soil.
Secondary succession	Succession in disturbed areas where soil remains (e.g., after fire).
Pioneer species	The first species to colonise new or disturbed environments.
Climax community	A stable, self-sustaining community at the end of succession.
Resilience	The ability of an ecosystem to recover after disturbance.

📌Introduction

Ecological succession describes how communities change over time, driven by species colonisation, competition, and modification of the environment. Succession increases biodiversity and complexity until a stable climax community is established. However, disturbances such as fire, storms, or human activity can reset succession. Ecosystem stability depends on resilience — the capacity to recover after such events

📌 Primary Succession

• Begins on bare rock (volcanic islands, retreating glaciers).
• Pioneer species (lichens, mosses) colonise first, breaking rock into soil.
• Soil formation allows grasses, shrubs, and eventually trees to grow.
• Increases organic matter, nutrient cycling, and habitat complexity.
• Takes hundreds to thousands of years to reach a climax community.

🧠 Examiner Tip: Distinguish clearly between primary and secondary succession — many students mix them up.

📌 Secondary Succession

• Occurs after disturbances that remove communities but leave soil intact.
• Faster than primary succession because soil and seeds remain.
• Common after forest fires, floods, or abandoned farmland.
• Communities rebuild through stages: weeds → grasses → shrubs → trees.
• Biodiversity recovers more quickly than in primary succession.

🧬 IA Tips & Guidance: Students can monitor succession in school grounds (e.g., abandoned plots) over months, recording species diversity.

📌 Climax Communities and Stability

• Climax community is the endpoint of succession: stable, high biodiversity.
• Composition depends on climate (e.g., tropical rainforest vs desert).
• Dynamic equilibrium: communities remain stable but not static.
• Disturbances (storms, fires) may shift communities into new stable states.
• Human activity (logging, farming) often prevents climax formation.

🌐 EE Focus: An EE could compare primary vs secondary succession in local ecosystems, using biodiversity indices to track recovery.

📌 Resilience and Disturbance

• Ecosystems vary in resilience — ability to bounce back after disturbance.
• High diversity often increases resilience by providing functional redundancy.
• Keystone species contribute to recovery capacity.
• Disturbance regimes (frequency, intensity) determine community pathways.
• Low resilience ecosystems risk collapse under repeated stress.

❤️ CAS Link: Students could support local ecological restoration projects, such as planting native species in degraded areas.

📌 Human Impacts on Succession

• Agriculture and urbanisation halt natural succession.
• Invasive species alter successional pathways by outcompeting natives.
• Fire suppression changes natural disturbance regimes, reducing biodiversity.
• Restoration ecology seeks to guide succession towards desired outcomes.
• Humans both hinder and manage succession processes.

🔍 TOK Perspective: Succession is often depicted as a linear pathway to climax. TOK issue: Do such models ignore the unpredictability and multiple possible outcomes of real ecosystems?

📝 Paper 2: Questions may involve distinguishing primary vs secondary succession, explaining resilience, or analysing biodiversity changes after disturbance. Data often include graphs of species richness over time.