The final stage of succession is called the climax or climax community (Clements, 1936; Shimwell 1971).
It is the final or stable community in a successional series. It is self-perpetuating and in equilibrium with the physical and biotic environment.
Climax communities undergo changes in structure as a result of birth, death and growth processes in the community.
There are following theories of the climax:
1. Mono-climax Theory:
According to the mono-climax theory of succession (Clements, 1936), every region has one climax community toward which all communities are developing. He believed that climate was the determining factor for vegetation and the climax of any area was solely a function of its climate. Various terms such as sub-climax, dis-climax, post-climax, and pre-climax are used to describe the deviations from the climatically stabilized climax. These communities, controlled by topographic, edaphic (soil), or biotic factors are regarded as exceptions by the supporters of the mono-climax view.
2. Poly climax Theory:
This theory was proposed by Tansley (1939) and later supported by Daubenmire (1966). The poly-climax theory of succession holds that many different types of vegetation as climax communities may be recognized in a given area. These will be climaxes, controlled by soil moisture, soil nutrients, activity of animals and other factors. According to this theory, climate is only one of the several factors, any of which may have a controlling influence on the structure and stability of the climax. This allows many climaxes in a climate region and is, therefore, called the poly-climax theory.
The difference between this theory and the mono-climax theory is largely a matter of emphasis on which factor is responsible for the stability of a climax. According to Krebs (1994), the real difference between two theories lies in the time factor of measuring relative stability. The climate varies on an ecological time scale as well as on a geological time scale. Succession in a sense, then, is continuous because we have variable vegetation approaching a variable climate.
3. Climax-pattern Theory:
Whittaker (1953) emphasized that a natural community is adapted to the whole pattern of environmental factors in which it exists; the major factors are: genetic structure of each species, climate, site, soil, biotic factors (activity of animals), fire, and wind, availability of plant and animal species, and chances of dispersal. According to this theory, climax communities are patterns of populations varying according to the total environment. There is thus no discrete number of climax communities and no one factor determines the structure and stability of a climax community.
Whereas the mono-climax theory allows for only one climatic climax in a region and the poly-climax theory allows several climaxes, the climax-pattern hypothesis allows a continuity of climax types varying gradually along environmental gradients and not clearly separable into discrete climax types.
4. Climax as Vegetation:
According to Egler (1954) one can say that “climaxes” in a broad sense are nothing more than totality of vegetation, itself He, thus, favours the study, of vegetation; as it is, with careful observations to explain and interpret past, present, and future conditions of particular communities.
We may conclude from these theories that the end point of succession is climax which is in itself not completely stable. The climate of an area has overall control on the vegetation; but within each of the broad climatic zones there are many modifications caused by soil, topography, and animals which lead to many climax situations. Climax communities do not necessarily represent a halt to successional change.