Chapter 4 (Part 1): Plant Succession
Chapter 4 (Part 1): Plant Succession
Fundamentals, Historical Milestones, Causes and Processual Mechanisms
1. Key Concepts and Definitions
Plant Succession
Gradual replacement of one plant community by another towards a climax, representing the culmination of vegetation for a given environment.Sere
The series of plant communities resulting from succession, or any recognizable individual stage in plant succession.Pioneer
A hardy species that invades a bare area and promotes conditions suitable for more exacting successor species.Ecesis
The complete process of establishment in a new area, from germination or vegetative rooting to reproduction.Reaction
The effect of vegetation on its site through changes in light, temperature, wind, soil organic matter, moisture and nutrients.Autogenic Succession
Succession in which the main changes are brought about by the plant community itself modifying its ecosystem.Allogenic Succession
Succession driven by external physical or biotic factors operating independently of the plants themselves.Important distinction: Autogenic succession is driven by community-induced environmental changes; allogenic succession is driven by external factors such as clearing, burning, grazing and landslides.
2. Historical Milestones in Succession Science
| Scientist | Year | Contribution |
|---|---|---|
| Richard Peters | 1806 | Recorded the departure of southern pine timber as evidence of vegetation change on the same soil. |
| Dawson | 1847 | Described localized vegetation shifts. |
| Henry David Thoreau | 1863 | First to coin the term "forest succession". |
| Cowles | 1899 | Investigated dynamic vegetation changes on sand dunes. |
| Frederic Clements | 1916 | Elaborated a unified theory of plant succession. |
Clements' three core tenets
- Vegetation changes continually through interactions between plant communities and habitat factors.
- Succession is inherently progressive and culminates in a stable climax.
- Succession is the progressive development of vegetation on the same site over time.
Historical sequence: Peters → Dawson → Thoreau → Cowles → Clements.
3. Causes of Plant Succession
Succession is governed by two broad sets of causes: initial causes and continuing causes.
A. Initial causes
Primary succession
- Erosion: Wind and water erosion, alluvial deposits, coastal sands, estuarine mud, sand dunes, landslips and screes.
- Physiography: Landform configuration assisting erosion and deposition.
- Elevation and subsidence: Geological or seismic disturbances creating bare riverbeds or new surfaces.
Secondary succession
- Climate: Drought, windthrow, snow-slides and frost.
- Physiography: Landslides removing vegetation from slopes.
- Biotic factors: Clear-felling, fire, overgrazing and land clearing by humans and animals.
Initial causes create a bare site or destroy pre-existing vegetation. Continuing causes subsequently drive community replacement.
4. Clementsian Six-Step Mechanism
The process proceeds through six principal stages, followed by stabilization or climax.
1. Nudation — Creation of a bare site
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2. Migration — Arrival of plant germules
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3. Ecesis — Establishment of colonizers
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4. Grouping and Aggregation — Population increase and spatial grouping
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5. Competition — Struggle for light, nutrients and moisture
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6. Reaction — Vegetation modifies site conditions
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Stabilization / Climax — Dynamic equilibrium
Explanation of the six stages
| Stage | Explanation |
|---|---|
| Nudation | Creation of a bare site devoid of vegetation by initial causes. |
| Migration | Movement of germules such as spores, seeds, fruits or offshoots from parent areas through wind, water or animals. |
| Ecesis | Successful germination, growth and reproduction of colonizers. |
| Grouping and Aggregation | Increase in populations and spatial grouping following reproduction. |
| Competition | Inter- and intra-specific struggle for limited light, nutrients and soil moisture as crowns approach or touch. |
| Reaction | Vegetation modifies its site by reducing ground insolation, moderating temperature, increasing humidity and adding organic matter. |
Climax / stabilization: The community reaches dynamic equilibrium with the regional climate and reproduces in situ.
5. Reaction: How Vegetation Modifies Its Site
Climatic effects
- Reduces ground insolation.
- Lowers daytime air temperature.
- Elevates night temperature.
- Increases relative humidity.
- Moderates temperature extremes.
Soil effects
- Adds organic litter and humus.
- Improves soil structure.
- Enhances water retentivity.
- Improves nutrient availability.
Reaction is a key mechanism through which vegetation changes the environment and facilitates the establishment of successor communities.
6. Kinds of Plant Succession
| Basis | Category | Definition and examples |
|---|---|---|
| Site moisture | Xerarch / Xerosere | Begins in extremely dry situations such as bare rock and sand dunes. |
| Site moisture | Lithosere | Xerarch succession on bare rock surfaces. |
| Site moisture | Psammosere | Xerarch succession on wind-blown sand. |
| Site moisture | Hydrarch / Hydrosere | Begins in water or extremely wet sites such as ponds, lakes, marshes and mudflats. |
| Site origin | Primary succession | Begins on bare sites that have never previously borne vegetation. |
| Site origin | Secondary succession | Begins after partial or complete destruction of original vegetation. |
Memory trick: Litho = rock; Psammo = sand; Hydro = water; Xero = dry.
7. Primary vs. Secondary Succession
| Feature | Primary succession | Secondary succession |
|---|---|---|
| Site origin | Bare site without previous vegetation. | Site after destruction of original vegetation. |
| Soil condition | Immature; low nutrients; poor moisture retentivity; little or no humus. | Relatively mature soil with residual fertility and humus. |
| Seed bank | Generally absent in the original bare-site condition described. | Residual seed reserves may remain. |
| Pioneer examples | Casuarina, Saccharum. | Macaranga, Trema, Woodfordia. |
| Progression rate | Extremely slow; may require centuries or millennia. | Comparatively rapid due to existing soil maturity. |
Conceptual distinction: Primary succession begins on a previously unvegetated surface; secondary succession begins where vegetation has been disturbed or destroyed.
8. Important One-Liner Facts
- Thoreau (1863): coined the term "forest succession".
- Clements (1916): developed the unified succession theory.
- Pioneer species tolerate strong sunlight, wide temperature ranges, strong winds and low soil fertility.
- Forest canopy closure reduces ground insolation.
- Forest canopy closure lowers daytime air temperature and elevates night temperature.
- Vegetation reaction increases relative humidity and organic matter.
- Primary succession begins on sites without previous vegetation.
- Secondary succession follows destruction of original vegetation.
- Lithosere occurs on rock; Psammosere occurs on sand.
9. Quick Revision Box
- Succession: Gradual replacement of plant communities.
- Sere: Series of communities or an individual seral stage.
- Pioneer: Hardy early colonizer.
- Ecesis: Establishment from germination to reproduction.
- Reaction: Vegetation modifies its own site.
- Autogenic: Community-driven change.
- Allogenic: Externally driven change.
- Thoreau: 1863, forest succession.
- Cowles: 1899, sand-dune vegetation.
- Clements: 1916, succession theory.
- Xerosere: Dry-site succession.
- Hydrosere: Wet-site succession.
- Lithosere: Bare rock.
- Psammosere: Sand.
10. Interactive MCQ Quiz
15 questions. Tap an option to see the correct answer and explanation straight away, then go to the next question.
Your score
Chapter 4 (Part 1) | Plant Succession
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