What is succession? What are the process of succession?

Succession is a gradual and visible directional change in community structure throughout the time.
It can also be defined as the gradual replacement of one community with another community till forming a stable climax community.


CAUSES OF SUCCESSION


1. Initial Causes -- Causes responsible for the destruction of existing habitat such as Climatic factor and biotic factor.

2. Continuing factors -- These are the process such as migration due to industrialization or urbanization, competition etc.

3. Stabilizing factors -- Causes which brings stability to the communities such as fertility of land, increase in temperature.

 TYPES OF succession 

Various types of succession have been grouped on the basis of different aspects. Two major types of succession are as follows....
 
  1. Primary succession -- It starts from the primitive sub-stratum, where was no previously any source of living matter.
  2. Secondary succession -- It starts from previously built-up sub-stratum with already existing living matter.

PROCESS OF SUCCESSION -- The whole process of succession is completed through a number of sequential steps as follows:

1. NUDATION -- Development of bare area without any form of life. The causes of nudation may be:
  a// Topographic -- Soil corrosion by water or wind, land slide, volcanic activity etc.
  b// Climatic -- Glaciers, Drought, storm etc. may destroy the community.
  c// Biotic -- Man may the cause and other factors are disease due to fungi and bacteria.

 2. INVASION -- It is the successful establishment of a species in a bare area. The whole process is completed in three stages...

  a// Migration -- The seeds, spurs of the species reach the bare area by wind, water, insects, birds etc.
 b// Ecesis -- After reaching the new area, the process of successful establishment of a species as result of adjustment with the existing environmental condition there.
 c// Aggregation -- After ecesis, as a result of reproduction, the individuals of the species increase in number.

 3. COMPLETION AND CO-ACTION -- After aggregation of a large number of individual species at that limited place, there developes competition mainly for the space and nutrients.
 individual of a species affects each other’s life in various ways, which is called as co-action.

 4.Reaction -- It is known as the modification of environment through the influence of the living organism on it. As a result of reactions, changes take place in soil, water, light intensity etc. of environment. Due to this change, becoming unsuitable for the existing community, which sooner or later replaced by another community.

 5. CLIMAX -- At last, when the final terminal community becomes more stabilized for a long time and it can maintain itself with the surrounding environmental condition. Hence this final community is not replaced by any other and is known as climax community and stage is known as climax stage.

Note: In an ecological succession the first and last community are known as pioneer and climax community. And all the middle community are known as seral community.


EXAMPLES OF SUCCESSION 

HYDROSERE -- It is the succession of plants which occur in an area of fresh water such as pond, lakes etc. Considering the simplest aquatic system i.e. pond, steps of hydrosere are as follows; 

1. Plankton Stage -- These are the pioneer community. Phytoplanktons and Zooplanktons like Blue-green algae, green algae, diatoms etc. grow and then multiply themselves in huge quantity.

2. Rooted Submerged Stage -- After the death and decomposition of Phytoplanktons, a soft mud developes at the bottom of the pond. So, water depth decreases and bottom level rises up where sunlight may penetrate making suitable for the growth of rooted Hydrophytes like Hydrilla, Elodia etc. forming a dense growth.

3. Rooted Floating Stage -- By now, due to formation of mud the pond becomes more shallower and leaves of the rooted Hydrophytes plants will be floating on water. Some floating plants like Azolla, Leman etc. also form association with rooted plants.
These plants enrich the water with minerals and organic matter.

4. Reed-Swamp Stage -- As water is enriched, which is suitable for the growth of amphibious plants like Typha, Sagittaria etc., which can survive in the land as well as water.

5. Sedge Meadow Stage -- As a result of high rate transpiration, there is loss of water and the mud is exposed to air, where nutrients like ammonia, sulphides etc. become oxidized to nitrates, sulphates etc. forming a suitable condition for the growth of grass and some herbs.

6.Woodland stage -- After some time the soil became more drier and now this area is covered by the shrubs like Bogwood, Salix, Cottonwood etc. who can tolerate bright sunlight and water lagging.

7. Forest Stage -- This is the climax community, where woodland community is invaded by several trees like Oak, Spruce, Fir etc. In moist areas, there develop rain forests and mixed forest in temperate areas.

 XEROSERE -- It is the succession of plants which occur in a dry area. Considering the simplest i.e. succession of plants on rock, which is also called as lithosere are as follows... 

 1. Crustose Lichens Stage -- Here the pioneer community start growing with less water presence and organic matter with heavy sunlight. These are the lichens like Rinodiha, Lecanora etc.

2. Foliose Lichens Stage - After some time crustose lichens are replaced by foliose lichens like Parmelia, Dermatocaprone etc. These community can absorb and retain more water and dust particles leading to formation of thin soil layer.

3. Moss Stage -- The developed thin soil layer favors the growth of some xerophytic mosses such as Turtula, Grimmia etc.  Now some lichens became dead due to competition, which increases the organic matter and thickness of soil.

 4. Herbs Stage -- The added minerals and soil promotes the growth of some herbs like Astrida, Poa etc.

 5. Shrubs Stage -- Due to presence of more soil, the habitat became suitable for the growth for shrubs such as Rhys, Phytocarpus etc. which starts migrating to that area.
 The soil is further enriched by this dense growth.

 6. Forest Stage -- After that some xerophytic trees invade that area. Further increase in humus content of the soil, favors the growth of more trees and finally becomes mesophytic. And there developes the climax community.