Ecological succession is the process by which the species composition of an ecosystem changes over time. It occurs through a predictable sequence of species replacements as the environment changes. There are two types of succession - primary succession, which establishes ecosystems in newly available habitats like volcanic landscapes, and secondary succession, which reestablishes ecosystems after a disturbance like a forest fire. Succession proceeds through stages from pioneer to intermediate to climax communities as species alter environmental conditions and facilitate the establishment of other species. Ecological succession is driven by both biotic changes from organisms as well as abiotic changes in the physical environment and is an ongoing, endless process as conditions continually change over geological timescales.

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PRESENTATION
ON

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Definition of
succession
Causes of
succession
Mechanism of
succession
Stages of
succession
Types of
succession
Content
s

3. What actually the succession
is?
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 Ecological Succession: The series of changes in
an ecosystem when one community is replaced
by another community as a result of changes in
biotic and abiotic factors.
 Occurs in all types of ecosystems i.e., forests,
ponds, coral reefs, etc.

4. Ecological succession is
characterised by
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 Increased productivity
 The shift of nutrients from the reservoir
 Increased diversity of organisms with increased
niche development
 Gradual increase in the complexity of food webs.

5. Ecological Succession
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6. Causes of plant succession:
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Autogenic succession- can be brought by changes in the soil caused by
the organisms there.
For example, when larger species like trees mature, they produce shade on to
the developing forest floor that tends to exclude light-requiring species.
Shade-tolerant species will invade the area.
Allogenic succession-caused by external environmental influences and not
by the vegetation.
For example, soil changes due to erosion, leaching or the deposition of silt and clays
can alter the nutrient content and water relationships in the ecosystems.

7. Causes of ecological
succession
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 Physical environment
 Natural disturbance
 Human disturbance
Can result in gradual changes in the physical
environment or from sudden disturbance.
 Clearing land
 Climate change
 Introduction of non native species
 Natural disasters such as volcanic, eruptions, forest
fires, hurricanes and floods.

8. Why Does Ecological Succession
Occur?
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• Because it is the process of life for plants, soil and
other living organisms.
• Because organisms alter soil structure, chemistry,
and microclimates, the species composition of
ecological communities constantly changes over time.
• Succession will continue until the environment
reaches it’s final stage…the Climax Community.

9. Mechanism of succession
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According to Clements, succession is a process involving several phases:
Nudation: Succession begins with the development of a bare site, called Nudation
(disturbance).
Migration: It refers to arrival of propagules.
Ecesis: It involves establishment and initial growth of vegetation.
Competition: As vegetation becomes well established, grow, and spread, various
species begin to compete for space, light and nutrients.
Reaction: During this phase autogenic changes such as the buildup of humus
affect the habitat, and one plant community replaces another.
Stabilization: A supposedly stable climax community forms.[

10. Stages of ecological
succession
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 Pioneer community
 Intermediate community
 Climax community

11. Types of succession
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• Primary succession
• Seconday succession

12. Types of succession
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Primary Succession
The process of creating and developing an ecosystem
in an area that was previously uninhabited.
Examples of uninhabited areas:
• Sides of volcanoes
• Sites of glacier recession

13. Examples of
Primary Succession
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14. 1. In this example, a volcanic eruption has destroyed the previous ecosystem.
2. The first organisms to appear are lichens.
3. Mosses soon appear, and grasses take root in the thin layer of soil.
4. Eventually, tree seedlings and shrubs sprout among the plant community.
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16. Secondary succession
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The disturbed area undergo series of changes similar to
primary succession in which smaller, faster growing species
are gradually replaced by larger and more stable species.
Secondary succession is a never ending process.

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20. AN EXAMPLE OF SECONDARY SUCCESSION7/15/202020

21. An example of Secondary Succession
by stages:
1. A stable deciduous forest community
2. A disturbance, such as a wild fire, destroys the forest
3. The fire burns the forest to the ground
4. The fire leaves behind empty, but not destroyed, soil
5. Grasses and other herbaceous plants grow back first
6. Small bushes and trees begin to colonize the area
7. Fast growing evergreen trees develop to their fullest, while
shade-tolerant trees develop in the understory
8. The short-lived and shade intolerant evergreen trees die as
the larger deciduous trees overtop them. The ecosystem is now
back to a similar state to where it began.
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Threats to Succession
• The grasses that move in as pioneer species are often
thought of as weeds
• The subsequent growth of shrubs are considered
undesirable "brush".
• Without these intermediate stages, the disturbed habitat
can't return to a natural forest.
• The fragility and stability of the ecological community are
dependent upon several factors.

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• Also, over long periods of time (“geological time”) the
climate conditions and other fundamental aspects of an
ecosystem change.
• These geological time scale changes are not observable
in our “ ecological” time, but their fundamental existence
and historical reality cannot be disputed.
• No ecosystem, then, has existed or will exist unchanged
or unchanging over a geological time scale.
ECOLOGICAL SUCCESSION NEVER
ENDS

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ENDLESS
ECOLOGICAL
SUCCESSION...

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References
Modern concepts of ecology - H D Kumar
https://en.wikipedia.org/wiki/Ecological_succession
https://www.britannica.com/science/ecological-
succession

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