The gradual replacement of one community by another in the development of vegetation towards a climax is the culmination stage in plant succession for a given environment.

1. Introduction
 The gradual replacement of one community by another in the
development of vegetation towards a climax which is the
culmination stage in plant succession for a given environment.
 The plant communities involved in the succession before the
climax is reached are called 'seres’.
 Sere is defined as the series of plant communities resulting
from processes of succession or any recognizable stage in
plant succession'.

2. EVOLUTION OF THE CONCEPT OF
PLANT SUCCESSION
 Richard Peters, who in 1806 described the departure of
southern pine timber as a proof of the tendency in the
nature to a change in products on the same soil.
 Dawson (1847) and Thoreau (1863) described the
changes in localized places. Thoreau who, first, used the
term ’forest succession’.

3. EVOLUTION OF THE CONCEPT OF
PLANT SUCCESSION
 Cawles (1899) described the change in vegetation on
sand dunes.
 Clements (1916) who developed the idea and elaborated
the theory of plant succession.

4. Concept of plant Succession
 There is a continual change in the vegetation as a result of
interaction of plant community and the habitat factors.
 The succession is inherently and inevitably progressive and the
end product is the climax.
 The succession is the progressive development of vegetation
on the same site in course of time.

5. Kinds of Plant succession
 Succession can be classified mainly in two ways:
 On the basis of moisture conditions of the place
 On the basis of presence or absence of vegetation in the place.

6. On the basis of moisture
conditions of the place
 On the basis of the moisture conditions, succession is classified
into:
 Xerarch succession which is defined as the succession
initiated in extremely dry situations such as bare rock,
wind blown sand, rocky talus slopes, etc.
 Hydrarch succession which is defined as the "succession
beginning in water, or very wet land as in ponds, lakes,
marshes, etc.' The various stages of this succession are
called Hydrosere.

7. On the basis of the presence or
absence of vegetation in the place
 On the basis of the presence or absence of vegetation in the place,
succession is classified into:
 Primary succession which is defined as the succession which
takes place on ‘sites which have previously not borne
vegetation'. Primary succession is, sometimes, termed as
Autogenic succession because it takes place as a result of
autogenic factors which are defined as the 'dominating
factors of change which are due only to the individuals in a
plant community.

8. On the basis of the presence or
absence of vegetation in the place
 Secondary succession which is defined as the succession
which takes place on site 'after the destruction of the whole
or part of the original vegetation'. This succession is,
sometimes, termed as Allogenic succession as it takes place
due to allogenic factors which are defined as the 'factors
which operate, independently of the plant themselves, to
alter the habitat gradually and thus cause changes in
vegetation.

9. Different types of habitats in
which succession takes place
 Hydrosere: succession occurs where water is plenty, e.g.
pond.
 Derosere: succession occurs on a dry soil or rock.
 Xerosere: succession occurs on dry habitat like dry desert
or bare rock
 Psammosre: succession which occurs on sand dunes.
 Halosere: succession which occurs on saline soil
 Lithosere: Succession on newly exposed rock surface
 Oxylosere: Succession on acidic soil

10. Causes of succession
 The causes of succession may be classified as under:
 Initial causes
 Continuing causes

11. Initial causes of primary
succession
 Erosion-Wind and water erode the soil and deposit it
elsewhere. Thus, new soils are created in the form of alluvial
deposits, coastal sands, estuarian deposits, sand dunes,
landslips and scree.
 Physiography- The configuration of the land surface is an
initial cause to the extent it helps the agents of erosion i.e.,
wind, water and gravity, to create new soils.
 Elevation and subsidence- Seismic disturbances result in
elevation and subsidence of the soil resulting in the formation
of new soils. Due to these disturbances, river beds are silted up
or the rivers change their courses leaving their original beds for
starting primary succession.

12. Initial causes of secondary
succession
 Climate- Climate is the initial cause when the vegetation is destroyed by
the action of drought, wind, snow or frost. For instance, a fair portion of a
forest may be killed by drought. If left to it self, secondary succession will
start on this bare area. Wind may lay bare an area by uprooting the original
crop. Snow may, similarly, destroy forest by sliding.
 Physiography - Physiography is the initial cause when configuration of the
land surface is responsible for the destruction of vegetation in combination
with some other factors. For instance, land slide may take place on a steep
slope, destroying the forest.
 Biotic factor- Biotic factor is the initial cause where a forest is destroyed as
result of the activity of man, his animals, or even wild animals. For
instance, a forest may be destroyed by reckless cutting, clearing, burning,
indiscriminate heavy grazing, etc.

13. Continuing causes
 Continuing causes-Continuing causes are those causes of succession which
help the development of plant communities and their replacement by other
plant communities. Thus, while the initial causes create suitable conditions
for starting succession, the continuing causes help in the formation of plant
communities and their gradual replacement by other communities leading to
a climax. They consist of the following:
 Migration;
 Ecesis or establishment;
 Grouping and aggregation;
 Competition; and
 Reaction.

14. Hydrosere or Hydrarch
 It is succession occurring in the aquatic environment. Such a type
of succession does not necessarily lead the aquatic communities
toward the development of land communities.
 If the body of water is large and very deep or very strong wave
action and other powerful physical forces are at work, the
succession results in a stable aquatic community in which any
considerable further change is hardly recognizable.
 Succession is recognizable only if the colonization of plant
communities takes place in artificial small and shallow ponds,
lakes, etc. where wave action speeds up the process by allowing
the erosion of soil towards edge regions. In this way, the filling
process also speeds up quickly and consequently the body of water
disappears within few years time.

15. The different types of vegetation at different depths in a
pond

17. Xerosere or Xerarch
 The original substratum is deficient in water and lacks any
organic matter, having only minerals in disintegrated
unweather state. The pioneers to colonize this primitive
substratum are crustose type of lichens, and through a series of
successive seral stages the succession finally terminates into a
forest which constitutes the climax community.
 The various stages in xerosere can be enumerated as follows—
 Lichen stage
 Moss stage
 Herbaceous stage
 Shrub stage
 Climax forest

18. Various stages in xerosere

19. Climax
 BCFT(1953) defines climax as the culmination stage in
plant/community succession for a given environment
 A climax which owes its distinctive characters to climatic factors in
conjunction with only such biotic influences as plants and animals
naturally occurring in the area, bring about
 This is also, sometimes, referred to as formation which is defined as
‘the major unit of vegetation comprising the climax communities of an
area uniform in its major physiognomic features’.
 Pro-climax, which is defined as a term applied to all communities that
suggest something of a permanence or extent of a climax but are not
typical of the existing climate'. It includes sub-climax, sere-climax,
pre-climax, post-climax and dis-climax.

20. Theories of Climax
 Monoclimax theory
 Polyclimax theory
 Mosaic theory
 Vegetational gradient and climax pattern theory

21. Aubreville's mosaic theory
 Aubreville proposed Mosaic theory of climax. In English
language, mosaic means a form or work of art in which designs
are made by fitting together differently coloured bits of stones.
Even if the pattern of fitting stone pieces is changed, the design
is still called mosaic.
 Aubreville believed that the forest is composed of a number of
irregular small units with one or few dominants, which develop
on more or less predictable but different lines. These small
units may be compared *to the small bits of stones of the
engineering mosaic.
 The pattern of mosaic of the climax community keeps on
changing continually and is never constant.

22. Whittaker's theory of vegetational
gradient and climax patterns
 Whittaker was of the view that there is no absolute climatic
climax for any area and the climax is a function of the sum
total of all the factors of a mature ecosystem, i.e., climate, soil,
other site factors, biotic influences, availability of species, their
characteristics, dispersal, etc.
 It is thus a partially stabilized steady state adapted to the
whole pattern of environmental factors in which it exists,
exhibiting similar or convergent patterns in adaptation to
similar environments but showing continuous change along the
various continuous environmental gradients.

23. Classification of climax
 Even though the concept of climax is still developing it is convenient for practical use to
classify the climax as follows:
 Climatic climax-It is the climax which owes its distinctive characters to climatic
factors in conjunction with only such biotic influences as plants and animals naturally
occurring in the area bring about.
 Edaphic climax-Edaphic climax is defined as a community which differs from the
climatic climax of the area owing to the influence of special soil factors'. In other
words, within the general climatic climax, there may be characteristic vegetation
locally due to the influence of soil peculiarities
 Pre-climax-Pre-climax is the plant community immediately preceding in seral
development the climatic climax of the region and found under conditions drier than
are usual in the climate of the region

24. Classification of climax
 Post climax- Post climax is 'a plant community more
exacting than the climatic climax of a given region and
found under exceptionally favorable site conditions within
that region’
 Biotic climax or subclimax- Biotic climax is 'a climax which
differs from the climatic climax of the area owing to the action
of biotic factors'. Sub-climax is a vegetation whose
development towards climatic climax has been arrested at
some stage short of the normal climax by the action of factors,
natural or artificial, other than the climate and which is more or
less stable under the prevailing conditions.

25. Importance of the study of plant
succession
 The study of plant succession is very important from the point of
view of silviculture because it helps in :
 Classification of forests into forest types--It is one of the bases for
classification of forests into forest types.
 Choice of species for artificial regeneration-The species to be raised
in a plantation have to be selected keeping in view the stage of
development which the soil has reached. If an attempt is made to raise
a climax species on soils which are still very immature, it would result
in failure.
 Determination of successional stage of economically most valuable
crop and the method of obtaining it- Knowledge of succession
shows how the composition of the crop is changing and will change in
future. It also indicates the factors by which the succession can be
altered to the best advantage of the people

26. Uses of succession
 Classification of forests
 Species choice for afforestation
 Evaluating the sites
 Delineating economic species

27. Thank You