Ecological succession, the process by which the structure of a biological community evolves over time. Two different types of succession—primary and secondary—have been distinguished. Primary succession occurs in essentially lifeless areas—regions in which the soil is incapable of sustaining life as a result of such factors as lava flows, newly formed sand dunes, or rocks left from a retreating glacier. Secondary succession occurs in areas where a community that previously existed has been removed; it is typified by smaller-scale disturbances that do not eliminate all life and nutrients from the environment. Primary and secondary succession both create a continually changing mix of species within communities as disturbances of different intensities, sizes, and frequencies alter the landscape. The sequential progression of species during succession, however, is not random.

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4 sequential processes of succession in an ecosystem:

1. Nudation:

The process of succession begins with the formation of a bare area or nudation by several reasons, such as oleanic eruption, landslide, flooding, erosion, deposition, fire, disease, or other catastrophic agency.

New lifeless bare areas are also created by man, for example, walls, stone quarrying, burning, digging, flooding large land areas under reservoirs, etc.

2. Invasion:

The invasion is the arrival of the reproductive bodies or propagules of various