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 reproduction and aggregate in a large population in the area and in consequence individuals of the species come close to each other.
3. Competition and reaction:
As the numbers of individuals of a species increase due to multiplication and all aggregate at the limited place, the competition for space and nutrition is started among them (intraspecific competition). They also compete with individuals of other species that may enter the area (interspecific competition).
All individuals also interact with the environment. Consequently due to increased intra-and interspecific competitions and other type of biotic and a biotic interactions, the environment is modified and progressively becoming unsuitable for the existing community which sooner or later is replaced by new invaders or another community (seral community).
Finding the modified environment more suitable more species enter the area and compete with the previous occupants. This results in a balance among the species in which the former species is brought down to a subdominant status or is completely eliminated. The addition of organic matter, nutrients and more moisture in the substratum by small plants make it suitable for larger ones.
Increase availability of food allows various kinds of animals to join the community and the resulting interactions further modify the environment and pave the way for fresh invasion by other species of plants and animals to move on the process of succession.
4. Stabilization or climax:
Eventually a stage is reached when the final terminal community becomes more or less stabilized for a longer period of time and it can maintain itself in the equilibrium or steady state with the climate of that area. Theoretically at least, this last serai stage is mature, self-maintaining, self reproducing through development stages and relatively permanent. The vegetation is tolerant of the environmental conditions it imposed upon itself.
This terminal community is characterized be equilibrium between gross primary production and total respiration, between the energy captured from sunlight and energy released by decomposition, between the uptake of nutrients and the return of nutrients by litter fall.
It has a wide diversity of species, a well-developed spatial structure, and complex food chains; and its living biomass is in a steady state. This final stable community of the sere is the climax community, and the vegetation supporting it is the climax vegetation.
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