a universal process of directional change in vegetation, on an ecological time scale. occurs when a series of communities replace one another due to large scale destruction either natural or manmade.
continously -one community replacing another community, until a stable, mature community develops.
The first plant to colonise an area is called the pioneer community. The final stage of succession iscalled the climax community.
The stage leading to the climax community are called successional stages
or seres. characterised by the following: increased productivity, the shift of nutrients from’ the reservoirs, increased diversity of organisms with increased niche development, and a gradual increase in the complexity of food webs.
Primary Succession
In primary succession on a terrestrial site the new site is first colonized by a few hardy pioneer species that are often microbes, lichens and mosses.
The pioneers through their death any decay leave patches of organic matter in which small animals can live.
The organic matter produced by these pioneer species produce organic adds during decomposition that dissolve and etch the substratum releasing nutrients to the substratum. Organic debris accumulates in pockets and crevices, providing soil in which seeds can become lodged and grow.
As the community of organisms continues to develop, it becomes more diverse and competition increases, but at the same time new niche opportunities develops.
The pioneer species disappear as the habitat conditions change and invasion of new species progresses, leading to the replacement of the preceding community.
Secondary Succession
Secondary Succession occurs when plants recognize an area in which the climax community has been disturbed.
Secondary Succession is the sequential development of biotic communities after the complete or partial destruction of the existing community.
This abandoned farmland is first invaded by hardy species of grasses that can survive in bare, sun-baked soil. These grasses may be soon joined by tall grasses and herbaceous plants.
These dominate the ecosystem for some years along with mice, rabbits, insects and seed- eating birds.
Eventually, some trees come up in this area, seeds of which may be brought by wind or animals. And over the years, a forest community develops. Thus an abandoned farmland over a period becomes dominated by trees and is transformed into a forest.
The differences between primary and secondary succession, the secondary succession starts on a well-developed soil already formed at the site. Thus secondary succession is relatively faster as compared to primary succession which may often require hundreds of years.
Autogenic and Allogenic Succession
When succession is brought about by living inhabitants of that community itself, the process is called autogenic succession, while change brought about by outside forces is known as allogenic succession.
Autotrophic and Heterotrophic succession
Succession in which, initially the green plants are much greater in quantity is known as autotrophic succession; 
and the ones in which the heterotrophs are greater in quantity is known as heterotrophic succession.
Succession would occur faster in area existing in the middle of the large continent. This is because, here all prop gules or seeds of plants belonging to the different seres would reach much faster, establish and ultimately result in climax community.
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