ECOLOGICAL SUCCESSION

• Biotic communities are dynamic in nature and change over a period of time.

• The process by which communities of plant and animal species in an area are replaced or changed into another over a period of time is known as ecological succession.

• Both the biotic and abiotic components are involved in this change.

• This change is brought about both by the activities of the communities as well as by the physical environment in that particular area.

• During succession both the plant and animal communities undergo change.

There are two types of successions

(i) Primary succession and

(ii) Secondary succession.

(i).Primary succession :

• Primary succession takes place an over a bare or unoccupied areas such as rocks outcrop, newly formed deltas and sand dunes, emerging volcano islands and lava flows as well as glacial moraines (muddy area exposed by a retreating glacier). where no community has existed previously.

• The plants that invade first bare land, where soil is initially absent are called pioneer species.

• The assemblage of pioneer plants is collectively called pioneer community.

• A pioneer species generally show high growth rate but short life span.

• Furthermore, primary succession takes a very long time as compared to secondary succession as the soil is to be formed during primary succession while secondary succession starts in an area where soil is already present.

• The community that initially inhabits a bare area is called pioneer community.

• The pioneer community after some time gets replaced by another community with different species combination.

• This second community gets replaced by a third community.

• This process continues sequence wise in which a community replaced previous by another community.

• Each transitional (temporary) community that is formed and replaced during succession is called a stage in succession or a seral community .

• The terminal (final) stage of succession forms the community which is called as climax community.

• A climax community is stable, mature, more complex and long lasting.

• The entire sequence of communities in a given area, succeeding each other, during the course of succession is termed sere.

• Succession that occurs on land where moisture content is low for e.g. on bare rock is known as xerarch.

• Succession that takes place in a water body, like ponds or lake is called hydrarch.

(ii).Secondary succession :

• Secondary succession is the development of a community which forms after the existing natural vegetation that constitutes a community is removed, disturbed or destroyed by a natural event like hurricane or forest fire or by human related events like tilling or harvesting land.

• A secondary succession is relatively fast as, the soil has the necessary nutrients as well as a large pool of seeds and other dormant stages of organisms.

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