Succession refers to change in a community following either physical or biological disturbance, when a farmland is abandoned, a forest develops after a series of temporary communities.
In a sense we may think of such temporary communities as developmental stages analogous to the life history stages through which many organisms pass before reaching adulthood.
The concept of succession was largely developed by the botanists Warming (1909) and Cowles (1899), who studied the stages of sand dune development.
It has been further elaborated by Clements (1916, 1936) who proposed a theory of plant succession and community development called the mono-climax hypothesis. Later on Tansely (1939) and Daubenmire (1966) proposed the poly-climax hypothesis.
Succession is a unidirectional change in the community structure. In simple words, succession may be defined as natural change in the structure and species composition of a community.
Ecological cession may be defined in terms of the following three parameters:
(a) It is the orderly process of community changes, which are directional and therefore, predictable,
(b) It results from the modification of the physical environment by the community, and
(c) It culminates in the establishment of as stable an ecosystem as is biologically possible on the given site.
According to Kerbs (1994), succession is the universal process of directional change in vegetation and can be recognized by the progressive change in the species composition of the community. In his words, the development of the community by the action of vegetation on the environment leading to the development of new species is called succession.
It is important to emphasize that the phenomenon of succession is “community controlled”. Each group of organisms changes its physical substrate and the microclimate (e.g., local conditions of light, temperature), thereby making conditions favourable for another group of organisms. In other words, we say that each species alters the environment in such a way that it can no longer grow so successfully as others.
When the site has been fully modified by biological processes, an ecological steady state is developed. The species involved, time taken and the degree of stability achieved depend on the topography or climate of the area, and other physical factors. But the process of succession itself is biological, not physical. Thus, the physical environment determines the pattern of succession but does not cause it.
Processes Causing Succession:
Since succession is a series of complex processes, it follows that there can be no single cause for it. The processes causing succession may be distinguished as initiating or initial causes, continuing or ecesic causes, and stabilizing or climatic causes.
The initial causes produce the bare area or destroy the original population in areas already vegetated. The deposition of sediment as alluvial fans at the mouth of a river illustrates the former and the wandering sand dune covering a forest, the latter. The ecesic causes produce the essential character of vegetational development, i.e. The successive plant populations.
They have to do with the interaction of vegetation and habitat and are directive to the highest degree. The climatic causes determine the nature of the climatic climax, i.e., the end point of succession. They have a profound effect in determining the population from the beginning to end, the number and kinds of stages as well as the reactions of the successive stages. While the process of succession in the tropics is similar to that in temperate regions, the plant populations are often quite different. This is due to the climate.