Ecological succession is the gradual process by which ecosystems change and develop over time, characterized by the replacement of species and changes in the environment. There are two main types: primary succession, which occurs in uncolonized areas, and secondary succession, which occurs in previously inhabited areas affected by disturbances. The process involves pioneer species that modify the environment, preparing it for other species to thrive, and the concept of climax communities has evolved, as most habitats experience ongoing disturbances.

2. The numbers and types of species
that live in them generally change
through time.
This is called ecological succession.
The species living in a particular
place gradually change over time as
does the physical and chemical
environment within that area.

3. Ecological succession is a
very important form of grown and
development of an ecosystem as a
whole.
It allows new areas to be colonized
and damaged ecosystems to be
recolonized, so organisms can
adapt to the changes in the
environment and continue to
survive.

4. Succession takes place because
through the processes of living,
growing and reproducing,
organisms interact with and affect
the environment within an area,
gradually changing it.

5. Fig 1: Ecological succession order

6. Succession is directional. Different
stages in a particular habitat
succession can usually be
accurately predicted.
These stages, characterised by the
presence of different communities,
are known as 'seres.

7. Ecological succession is the
gradual process by which
ecosystems change and develop
over time.
Nothing remains the same and
habitats are constantly changing.
There are two main types,
primary succession and secondary
succession.

8. Succession occurs on many
different timescales, ranging from
a few days to hundreds of years
Fig 2: Succession stages

9. Primary Succession
Primary succession occurs in an
area that has never before been
colonized. Generally, the area is
nothing but bare rock. This type of
environment may come about
when
a) Lava flows from a volcano and hardens into rock.
b) A glacier retreats and leaves behind bare rock.
c) A landslide uncovers an area of bare rock

10. Fig 3: Primary Succession

11. The first species to colonize a
disturbed area such as this are
called pioneer species.
They change the environment and
pave the way for other species to
come into the area.
Pioneer species are likely to include
bacteria and lichens that can live on
bare rock.
Along with wind and water, they
help weather the rock and form
soil.

12. Once soil begins to form, plants
can move in.
At first, the plants include grasses
and other species that can grow
in thin, poor soil.
As more plants grow and die,
organic matter is added to the
soil. This improves the soil and
helps it hold water.

13. Fig 4: Pioneer species

14. Secondary Succession
Secondary succession occurs in a
formerly inhabited area that was
disturbed. The disturbance could
be a fire, flood, or human action
such as farming.
This type of succession is faster
because the soil is already in
place.

15. Fig 5: Secondary succession

16. In this case, the pioneer species
are plants such as grasses, birch
trees, and fireweed.
Organic matter from the pioneer
species improves the soil. This
lets other plants move into the
area.

17. Fig 6: Pioneer species

18. •Secoundary Succession.
•1st year after forest fire, flood,
or farmer abandons a field:
Weeds grow,
2nd year: Seeds blown in or
carried in by animals become
new weedy
5 to 15 years: Small pines begin
growing in the area, gradually
become a forest

19. Climax Communities
Ecologists assumed that
successions always ends with a
final stable stage. They called this
stage the climax community.
Today, most ecologists no longer
hold these views. They believe that
most of communities are
disturbed too often to become
climax communities.

20. Fig 7: Climax Communities