ECOLOGICAL SUCCESSION

Succession is a series of complex processes taking place in the environment due to various driving forces governed by nature. The main causes leading to succession are climatic factors such as erosion, wind, fire, and volcanic activities. The biotic or living forces which drive the process of ecological succession are processes such as migration, aggregation, competition, reaction, etc. that cause changes in the population for short durations.

Ecological succession may be classified into various types depending on different parameters. However, the two main types of succession may be grouped as primary succession and secondary succession.

There are two main types of succession, primary and secondary.

Primary Succession

·         Primary succession is the series of community changes which occur on an entirely new habitat which has never been colonized before. For example, a newly quarried rock face or sand dunes.

Primary succession begins in barren areas, such as on bare rock exposed by a retreating glacier. The first inhabitants are lichens or plants—those that can survive in such an environment. Over hundreds of years these “pioneer species” convert the rock into soil that can support simple plants such as grasses. These grasses further modify the soil, which is then colonized by other types of plants. Each successive stage modifies the habitat by altering the amount of shade and the composition of the soil. The final stage of succession is a climax community, which is a very stable stage that can endure for hundreds of years.

Secondary Succession

·         Secondary succession is the series of community changes which take place on a previously colonized, but disturbed or damaged habitat. For example, after felling trees in a woodland, land clearance or a fire.

Secondary succession follows a major disturbance, such as a fire or a flood. The stages of secondary succession are similar to those of primary succession; however, primary succession always begins on a barren surface, whereas secondary succession begins in environments that already possess soil. In addition, through a process called old-field succession, farmland that has been abandoned may undergo secondary succession.

 

Primary Succession:

1. It occurs in an area which has been bare from the beginning.

Primary Succession

2. Soil is absent at the time of beginning of primary succession.

3. There is no humus in the beginning.

4. Reproductive structures of any previous community are absent.

5. Pioneer community cotnes from outside.

6. In the beginning the environment is very hostile.

7. Serai communities are many.

8. Primary succession takes a long time for completion, 1000 years or more.

Secondary Succession:

1. Secondary succession occurs in an area which has been denuded recently.

2. Soil is present in the area where secondary succession begins.

3. Humus is present from the very beginning.

4. Reproductive structures of the previous occupants are present in the area.

5. Pioneer community develops partly from previous occupants and partly from migrants.