Environmental Biology Prof.(Dr.) Punam Jeswal Head M.Sc semester IV Botany Department

CONCEPTS OF CLIMAX

According to classical ecological theory, succession stops when the sere has arrived at an equilibrium or steady state with the physical and biotic environment. Excluding prime disturbances, it will persist indefinitely. This end point of succession is called climax. The final or terminal and more or less stabilised community in succession that is able to established equilibrium with the environment condition of that area, was termed climax by Clements (1916). It is self-perpetuating and in equilibrium with the physical and biotic environment and represent a steady state of species composition, community structure and energy flow. The final or stable community in a sere is the climax community or climatic vegetation. The final community is not replaced.

According to Clements (1916, 1935), Climax has the following Three Principal Characteristics:-

1) Unity :- Climax is a unit. All the species are not taken as an organized unit. Life or growth forms of plants indicate the climate type. In other words, climax is a unit, which acts as the index of climate of an area.

2) Stability :- The form of climax community is more or less stable with the climate. This climax community can not replaced through competition. In other words, according to the Clements in a particular climate area there may be develop climax community only with a few characteristic dominant species.

3) Origin and Phylogenetic Relations :- Climax community is treated as an equivalent to an organism, like which it takes birth, grows and develops and become mature. Clements designated it a Super-organism. In any climatic region, the developmental stages of the climax community have their own characteristics, which reflect the type of climate. Climax communities undergo changes with the changes of time and climate.

Theories Interpreting Climax There have been put three popular theories about the climax concept in ecology :-

1) MONOCLIMAX THEORY (or CLIMATIC CLIMAX THEORY) Monoclimax (or climatic climax theory) is developed by Federic Clements and supported by; Cowles, Ranganathan and Puri, but strongly objected by Daubenmire (1968).This theory recognizes only one climax, determined solely by climate, no matter how great the variety of environment conditions is at the start. According to the monoclimax theory of succession, within a given every region has one climax community towards which all communities are developing. Climax is determined by the regional climate. The processes of succession and modification of environment overcome the effects of differences in topography, parent material of the soil, biotic factor and other factor. The whole area would be covered with uniform plant community. The other communities existing besides the climax community in that area, are called as subordinate communities. The subordinate communities may be , pro-climax ,post-climax, pre-climax ,sub-climax and disclimax etc.

2) POLYCLIMAX THEORY :- This theory was proposed by Tansley (1939) and later supported by Daubenmire (1966). The theory consider that the climax vegetation of a region consists of not just one type but a mosaic of vegetation climaxes controlled by soil moisture, soil nutrients, topography, slope exposure, fire and animal activity. The polyclimax theory holds that many different types of vegetation as climax communities may be recognized in a given area controlled by a number of factors besides the climatic conditions of a geographical area. So the climax stages may be named depending upon the nature of the factor in stabilization for e.g. topographic climax, biotic climax, edaphic climax, fire climax etc.

3) CLIMAX - PATTERN HYPOTHESIS :- R.H. Whittaker (1953), proposed a variation of the polyclimax idea, the climax pattern hypothesis. Whittaker (1953) significance 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

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.

Types of Climax :-

Climatic Climax :- In this climax, the climax community of the succession is determine by the climate of the region. * The climatic climax have only one climax community.

Edaphic Climax :- The climax community is determined by the soil (edaphic factor ) of the region. * The edaphic factors may includes soil moisture, topography, soil texture and soil nutrients.

Catastrophic Climax :- Here climax community is vulnerable to many catastrophic events such as wildfire, snowfall and floods. * The catastrophic factors replaces the climax community completely and this area will be immediately invade by the new species.

Disclimax :- When a stable community, which is not the climatic or an edaphic climax for the given site, is maintained by man or his domestic animals, it is designated as disclimax (disturbance climax) or anthropogenic subclimax (man-generated).

Subclimax :- The stage in succession just preceding the climatic climax community was called a sub-climax.

Pre-climax or Post-climax :- In certain areas different climax communities develop under similar climatic conditions. If the community has life forms lower than those in the expected climatic climax, it is called pre-climax; a community that has life forms higher than those in the expected climatic climax is post-climax.

CHARACTERISTICS Of A CLIMAX COMMUNITY :-

* The vegetation is tolerant of environmental conditions. * The vegetation of the climax community will have high ecological amplitude. * They show rich diversity in species composition and a well drained spatial structure. * The community possesses a complex food chain system. * Individuals in the climax stage are replaced by others of the same kind. Thus the species composition maintains equilibrium. * The ecosystem will be balanced and self-sustainable. * There is equilibrium between gross primary production and total respiration. * The energy used from the sunlight and energy released after decomposition will be balanced. * The uptake of nutrients from the soil and the release of nutrients back to the soil by decomposition will be balanced. * It is an index of the climate of the area. The life or growth forms indicate the climatic type.