The gradual and fairly predictable change in the composition of different species in a given area is known as ecological succession. During ecological succession, the population of certain species increases, while that of many others may decline or may even disappear. All communities undergo constant changes in their composition and structure in response to changes in environmental conditions. These changes take place in a sequential and orderly manner, leading to a climax community, which is in near equilibrium with the environment. In the process of ecological succession, the sequence of communities that replace one another in a given area is known as a sere or seres. Each transitional community is called a seral community or a seral stage.
Primarily, there are two causes for ecological succession, they are biotic factors and physiographic factors. Biotic factors include interactions between different organisms in a community, leading to changes in composition, structure and functions in that community. Physiographic factors, on the other hand, include physical factors.
Furthermore, ecological succession is of two types: primary and secondary. Primary succession is a type of biotic succession that takes place in areas where no life previously existed. Conversely, secondary succession is a type of biotic succession that takes place in areas that once had an existing biotic community.
Based on the nature of the habitat, ecological succession of plants is categorised as hydrarch, mesarch and xerarch. When succession takes place in regions with plenty of water is known as hydrarch. On the other hand, when succession takes place in regions with moist, well-aerated soil, it is known as mesarch. Finally, succession in regions with minimum moisture, such as rocks and deserts, is known as xerarch.
The species that invades a bare area during primary succession is known as the pioneer species and it varies depending on the area where succession is taking place. Primary succession in water, the pioneer species is usually phytoplankton. Here, once again, the stable climax community is the forest. Thus, with the passage of time, a water body gets converted into land. The species that invade in a secondary succession is dependent on factors such as soil conditions, availability of water and type of seeds, to name a few.
So we can say that the climax community attained due to ecological succession in a given area is the result of the interactions of existing species with each other and also with the environment.