Every community undergoes a series of changes until a group in the area. This is called biotic succession. Succession is a sequence of changes in time of the species which inhabit an area from an initial pioneer community to a final climax community. In other word, the development of community by the action of vegetation on the environment leading to the development of new species is called succession.
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Succession involves a series of complex processes. It is because of this reason that the occurrence of succession is associated with many causes. These exist three primary causes of succession.
(i) The first cause is concerned with climatic and biotic in nature. The climatic causes are erosion, deposits, wind and fire etc. All of these are responsible for destroying the existing population in the concerned area.
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(ii) The second cause is concerned with migration, aggregation, competition reaction etc. These are responsible for changing the soil features of this area.
(iii) The third cause is concerned with factors such as climate of the area responsible for stabilisation of the community.
Types of Succession
The succession is of different types, which are as under:
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(1) The succession which starts from a primitive substrate without any previous living matter is called primary succession. It starts on an area which is not occupied previously by a community.
(2) The succession starting from an area where living matter already exists is known as secondary succession. Secondary succession is faster than primary succession.
(3) In case the existing community causes its own community as a result of its reaction with the environment, it is known as autogenic succession.
(4) In case the replacement of one community takes place by another due to forces other than the effects of communities on the environment, the succession is called allogenic succession. Such a kind of succession may occur in highly disturbed area or in ponds where the nutrients and pollutants enter from outside which in turn modify the environment and thus communities.
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(5) The early and continued dominance of autotrophic organisms such as green plants is called autotrophic succession. This type of succession takes place in an inorganic environment.
(6) The early dominance of heterotrophic organisms such as bacteria, fungi, animals and actinomycetes is called heterotrophic succession.