The complete process of a primary autotrophic ecological succession involves the following sequential steps, which follow one another:

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 organisms and their settlement in the new or bare area. Hants are the first invaders (pioneers) in any area because the animals depend on them for food. The invasion includes the following three steps:

(1) Dispersal or migration:

The seeds, spores or other propagules of the species reach the bare area through the agency of air, water or animals. The process starting from the time a propagule leaves the parent plant to the time it arrives the bare area is called migration.

(2) Ecesis:

This is the successful establishment of migrated plant species into the new area. It includes germination of seeds or propagules, growth of seedlings and starting of reproduction by adult plants only a few immigrant propagules are capable of doing this under primitive hard conditions, and thus most of them disappear.

(3) Aggregation:

This final stage of invasion, the successful immigrant individuals of a species increase their number by