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Depending upon the nature of bare area on which it develops, the succession may be of two kinds primary and secondary:
1. Primary succession:
When the succession starts on the extreme bare area on which there was no previous existence of vegetation it is called primary succession or preserve.
This succession starts in the areas of extreme conditions and the process terminates after a long series of intermediate stages.
2. Secondary succession:
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This type of succession starts on the secondary bare area which was once occupied by original vegetation but later became completely cleared of vegetation by the process called denudation. This denudation process is brought about by the destructive agencies, such as fire, cultivation, strong winds, and rains.
When the existing vegetation of an area becomes completely destroyed by destructive agents, it becomes naked or bare. Such a bare area is termed denuded area or secondary bare area. The succession progressing on such an area is also termed sub-sere. Secondary succession has fewer stages than the primary succession and the climax is reached very quickly in the secondary succession.
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The primary and secondary successions may be of the following types:
(a) Hydrosere:
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The plant succession which starts in the aquatic environment is called “hydrarch.” A series of changes taking place in the vegetation of hydrarch is called hydrosere.
(b) Halosere:
It is special type of sere which begins on a salty soil or in saline water.
(c) Xerosere:
When the vegetational succession develops in xeric or dry habitat, it is called xerarch or xerosere.
Xerosere may be of two types:
(i) Psammosere:
It refers to the vegetational succession that begins on the sandy habitat.
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(ii) Lithosere:
It refers to the succession that occurs on the rock surface.
(d) Serule:
It refers to the miniature succession of micro-organisms, such as bacteria and different types of fungi on the fallen logs of decaying wood, tree bark, etc. Irrespective of the types of succession, all the seres generally lead the plant communities towards the climax stage of mesic community (mesophytic or mixed mesophytic forests).
