Fundamentals of Ecology 3. Explain the stages in hydrosere.
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4. Describe the sequential stages in lithosere.
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8.6 CLIMAX COMMUNITY
The end product of succession after seral communities is the climax community,
and it is a relatively stable community. It is generally believed that once the climax
is attained the community does not change at all, but this is not exactly so, climax
communities may also be changed by aging, storm, disease and by other biotic
and abiotic factors.
Hanson and Churchill (1961) characterized a climax community as:
i. The climax community is in steady state regarding its productivity, structure
and population.
ii. There is a diversity, stability, and homogeneity of the species populations
within and between the stand of the same climax community.
iii. Each stand is self-maintaining and long persisting.
iv. Replacement and fluctuation changes are operative on a continuous basis
within the climax, while all environmental factors determine its composition
and population so that there is a mosaic of climax types corresponding to the
mosaic of habitats.
8.6.1 Monoclimax Concept
This concept was advanced by an American plant ecologist E.E. Clements in
1916. According to him, in a climatic region, only one true climax community is
possible which is mainly controlled by the climatic factors. Such a climax is,
therefore, climatic climax. It is not affected by soil or topography. Edaphically
controlled stable communities are exceptions, and are not true climax.
In order to account for a variety of more or less stable communities but different
from regional climatic climax, Clements proposed four other terms:
• Subclimax- succession gets arrested at a stage which persists for a long time in
response to physiological or edaphic factors, before being replaced by the climatic
climax;
• Disclimax- the vegetation replacing the true climax as a result of some persistent
biotic disturbance in the environment, e.g., the grasslands in the Gangetic Plains
which occur due to grazing in a deciduous forest climax;
• Preclimax- slightly drier localities in a given climatic climax area may have a self-
perpetuating community different from the climatic climax, e.g., some of the pine
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forests in the Himalaya; Ecological Succession and
Climax
• Post-climax- slightly “better moisture” areas in the climatic climax region
may support a different yet self-perpetuating community, e.g., Terminalia
arjuna community growing near river banks in a dry deciduous forest climax.
The monoclimax concept has been severely criticized on the ground that in the
concept regionally prevailing undisturbed vegetation occupying the largest part
of the land surface was regarded as real climax and other stabilized plant
communities in the same area were recognized as subclimaxes which only
theoretically could be replaced by the climax.
8.6.2 Polyclimax Concept
This concept was advocated by Whittaker (1953) and supported by Tansley.
According to this concept a climax reflects not only the climatic factors but also
other factors of the environmental complex, viz., edaphic, biotic, etc. The climax
can be of several other kinds which are different from the climatic climax of the
area. Climate is not the only factor that determines the climax in a large area.
Other factors like edaphic, topographic, and biotic factors are equally important
so that edaphic, topographic and biotic climaxes may occur in localized regions
within the same climatic zone.
Tansley (1920) recognized the existence of a number of climax communities,
forming a mosaic corresponding to the mosaic of habitats and suggested a
polyclimax theory. However, this view too identified a climatic climax community
that is the stable and most extensive in different habitats for an area. Tansley
recognized following climax types:
i. Climatic climax: Climax under normal conditions of climate, soil and
topography and no disturbance.
ii. Edaphic climax: Substrate peculiarities are well pronounced to produce
self-perpetuating vegetation, which is different from the climatic climax of
the area.
iii. Topographic climax: Changes in the topography enough to cause variant
microclimates, each giving rise to self-perpetuating vegetation.
iv. Fire climax: Recurrent burning of vegetation eliminates fire-sensitive
species and self-perpetuating vegetation develops.
v. Zootic climax: Self-perpetuating community in response to zoological
factors e.g., grazing gives rise to zootic climax of grassland.
Climatic, edaphic and topographic climaxes are primary climaxes, while fire
and zootic climaxes are secondary disclimax.
8.7 ECOLOGICAL ADAPTATIONS
Adaptations are structural and functional characteristics which organisms have
developed during the course of evolution enabling them to survive and reproduce
in a particular environment. The term adaptation has therefore an evolutionary
significance.
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