Ecological succession describes the natural process of environmental change through which biological communities develop over time. Primary succession occurs in areas without previous life, like new lava flows, while secondary succession follows a disturbance in an existing ecosystem. Succession proceeds through a series of changes as pioneer species like lichens establish and modify the environment, allowing other species to colonize until a climax community develops.

1. CHANGES IN ECOSYSTEMS:
ECOLOGICAL SUCCESSION
Course 19 – Fundamental of Ecology
Course Instructor:
Arbaz Madni
Department of Environmental Sciences
NFC Institute of Engineering & Technology, Multan

2. DEFINITION:
• Natural, gradual changes in the types of species
that live in an area; can be primary or secondary
• The gradual replacement of one plant community
by another through natural processes over time

3. THERE ARE TWO MAIN TYPES OF
ECOLOGICAL SUCCESSION
• Primary Succession: The process of creating life in an
area where no life previously existed.
• Secondary Succession: The process of re-
stabilization that follows a disturbance in an area
where life has formed an ecosystem.
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4. PRIMARY SUCCESSION
• The development of an
ecosystem in an area that has
never had a community living
within it occurs by a process
called PRIMARY SUCCESSION.
• An example of an area in
which a community has never
lived before, would be a new
lava or rock from a volcano
that makes a new island.
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5. PRIMARY SUCCESSION
• Begins in a place without any soil
• In the beginning there is only rock, sand, volcanic ash.
• Since there is no soil, there is no community.
Why is there no soil?

6. PRIMARY SUCCESSION
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7. PRIMARY SUCCESSION
• Lichens begin growing on the rocks. Over many
years lichens break down rock into sand.
• Weathering and erosion break down rock into sand.

8. PRIMARY SUCCESSION
• Lichens that do not need soil to survive
• Called PIONEER SPECIES

9. PRIMARY SUCCESSION
• Lichens grow larger. Some die. Decomposers arrive
and break down the lichens. The dead lichens and
waste materials of the decomposers enrich the
sand. Nitrogen cycle begins. Eventually enough
nutrients enter the sand and it becomes soil.

10. http://www.life.uiuc.edu

11. PRIMARY SUCCESSION
• Seeds are blown in by the wind or carried in by
animals. Simple plants like mosses can grow in the
new soil
• The plants grow and the soil gets enriched as plants
die..

12. PRIMARY SUCCESSION
• Herbs and weeds can grow in the thicker, enriched
soil

13. PRIMARY SUCCESSION
• The simple plants die, adding more organic material
• The soil layer thickens, and grasses, wildflowers, and
other plants begin to take over
http://www.cwrl.utexas.edu

14. PRIMARY SUCCESSION
• Medium sized animals and birds make this
their habitat.
• The vegetation grows closer together,
reducing the amount of space available for
growing.
• Competition between lichen and shrubs for
the same space. Eventually one species
(lichen) will die out (or move) and the other
species will survive (shrubs).

15. PRIMARY SUCCESSION
• These plants die, and they add more nutrients to
the soil
• Shrubs and tress can survive now

16. PRIMARY SUCCESSION
• Insects, small birds, and mammals have begun to
move in
• What was once bare rock now supports a variety of
life
http://p2-raw.greenpeace.org

17. PRIMARY SUCCESSION
• These plants die, and they add more nutrients to
the soil
• Now larger trees can grow: Beech, Oak, Walnut,
Maple…

18. THE CLIMAX COMMUNITY
• A climax community is a mature, stable community
that is the final stage of ecological succession. In an
ecosystem with a climax community, the conditions
continue to be suitable for all the members of the
community.
• Any particular region has its own set of climax
species, which are the plants that are best adapted
for the area and will persist after succession has
finished, until another disturbance clears the area.
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19. THESE ARE CLIMAX COMMUNITIES
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20. • Two main physical factors determine the nature of
the community that develops in an area. These are
temperature and the amount of rainfall.
• If we place the amount of rainfall on a graph’s “x”
axis, from 0-10, 10-20,and 20-30+ inches and the
temperature along the “y” axis from hot, moderate,
to cold, the various types of ecosystems will fit into
the graph based on the conditions that they require.
Temperature
Cold Cold desert Tundra Taiga
Moderate Temperate forest Grassland Deciduous forest
Hot Hot desert Savanna Tropical forest
Rainfall (inches) 0-10 10-20 20-30+
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21. A SUMMARY OF CHANGES THAT OCCUR
DURING SUCCESSION:
• Pioneer species colonize a bare or disturbed site. Soil building.
• Changes in the physical environment occur (e.g., light,
moisture).
• New species of plants displace existing plants because their
seedlings are better able to become established in the
changed environment.
• Newly arriving species alter the physical conditions, often in
ways that enable other species to become established.
• Animals come in with or after the plants they need to survive.
• Eventually a climax community that is more or less stable will
become established and have the ability to reproduce itself.
• Disturbances will start the process of succession again.
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22. THREATS TO CLIMAX COMMUNITIES
• Forest Fires
• Humans building cities and roads
• Flooding, Volcanic eruptions
• Clearing a community for agricultural
purposes
• Anything that destroys the existing
community, but much of the soil remains.
Sometimes, some of the organisms remain
as well.

23. SECONDARY
SUCCESSION

24. SECONDARY SECCESSION

25. SECONDARY SUCCESSION
• Organisms are destroyed but the soil is safe.
• The soil already contains the seeds of weeds,
grasses, and trees. More seeds are carried to the
area by wind and birds.
• Succession begins again but the primary species
are different.
• Because soil is present, this succession is faster.

26. ECOLOGICAL SUCCESSION
•N

27. SECONDARY SUCCESSION ON AN
ABANDONED CORNFIELD

28. SECONDARY SUCCESSION
• 1. Some seeds in the
soil begin to grow.

29. SECONDARY SUCCESSION
• Larger shrubs move in.

30. SECONDARY SUCCESSION
• 3. Fast growing trees
(such as pines)
move in
• 4. These are
followed by slower-
growing hardwood
trees

31. http://www.ux1.eiu.edu

32. http://www.agen.ufl.edu

33. CLIMAX COMMUNITY
• A stable group of plants and animals that is the
end result of the succession process
• Does not always mean big trees
• Grasses in prairies
• Cacti in deserts

34. • Insects
• Nationwide, 70 million acres of public and private
lands are at serious risk from insects and diseases
• Across the South, one of the biggest forest
management challenges is the Southern Pine Beetle.
Attacking timber stands throughout the region, it is
estimated that 57 million acres are at risk of infestation.
From 1999 to the present, the Southern Pine Beetle
outbreak has caused timber value losses of over $1.5
billion.
Gypsy Moth, Lymantria dispar
(Linnaeus) female
Photo from USDA APHIS PPQ archives

35. • Diseases
• Forest pests and disease have seriously harmed the environment and have
imposed significant cost to the U.S. economy. Exotic pests and pathogens,
such as the chestnut blight, Dutch elm disease, and beech bark disease have
had a profound effect on Eastern forests.
• Management of these pests and diseases has been impacted by a variety of
factors such as forest fragmentation, increasing human population, and the
expansion of invasive species.
• Prompt identification and treatment of forest diseases often means the
difference between losing or saving a valuable forest stand.
Annosum Root Disease

36. • Invasive Plants
• Invasive species have been characterized as a “catastrophic
wildfire in slow motion.” Thousands of nonnative invasive plants
have infested millions of acres of land and water across the
Nation.
• These invaders cause massive disruptions in ecosystems by
reducing biodiversity and degrading the health of our nation’s
forests, prairies, mountains, wetlands, rivers, and oceans. They
have the capacity to dominate, overwhelm, or wipe out
native species.
• The financial impact from invasive species infestations in the
United States has been estimated at $138 billion per year in
total economic damages and associated control costs.
Congongrass Kudzu

37. • Human Development

38. QUESTIONS
1. What is the difference between primary succession
and secondary succession?
2. What is a pioneer species?
3. What is the role of lichens in primary succession?