Ecological Succession is defined as “a series of changes in an ecological system across time.” It can be defined simply as the sequence of species colonisation of an ecosystem from a barren or infertile piece of land. There are two types of Ecological Succession, i.e., Primary Succession and Secondary Succession.

In Primary Succession, living creatures inhabit newly exposed or newly created rock for the first time. Secondary Succession occurs when a previously inhabited area is disturbed and then recolonised after the disruption. Continue to read the article to learn the definition, types, process, and examples.

Ecological Succession Definition

An ecosystem develops and stabilises through the process of ecological succession. It is a process of change in the species structure of an ecological community over time from a pioneer community that sets first in a barren land to the climax community.

What is Ecological Succession?

The biotic community is a dynamic community. By interaction with the biotic and abiotic community, there is a change constantly occurring in an ecosystem. These changes finally lead to a community near equilibrium with the environment and are called a climax community.

The gradual and predictable changes in the species composition of a given area are collectively called ecological succession. Some species colonise an area during succession, and their populations become more numerous, whereas populations of other species decline and even disappear.

Fig: Ecological Succession

Characteristics of Ecological Succession

The ecological succession has the following characteristics:
1. It is a systematic process.
2. It involves changes in species structure and also increases the diversity of species.
3. The succession takes place due to changes in the physical environment and population of the species.
4. The changes that occur are directional and take place as a function of time.
5. Succession works in a stabilised ecosystem.
6. The population of decomposer components becomes significant.
7. The changes are calculable.
8. The simple food chains will be replaced by complex food chains.

Ecological Succession Causes

The causes of ecological succession are mainly three types. These are as follows:

1. Initial or initiating causes– These causes include both biotic and climatic. It has factors like erosion, wind, fire, natural disasters, etc. These causes heavily affect the population of that locality.
2. Ecesis causes- These causes are also known as continuing causes. These can modify the population to adapt to several conditions of the environment. It includes several factors like aggregation, competition, migration, etc.
3. Stabilising causes- These causes bring stability to the communities. It has several factors like the nature of the climatic condition of the area, fertility of land and abundance of availability of minerals, etc.

Types of Ecological Succession

Some of the major types of ecological succession are as follows:
(a) Primary succession: It starts in a barren area, never having vegetation of any type where no living organism ever existed. Some bare primary areas are the newly exposed seafloor, igneous rocks, sand dunes, new cooled lava sediments, newly submerged areas, etc. As there is no soil, and the conditions are too hostile to sustain life thus, the succession is slower. It usually takes several hundred to a thousand years for establishing a biotic community depending upon the substratum and the climate.
(b) Secondary succession: It starts in areas that somehow lost all the living organisms that existed there. Since some soil or sediment is present, succession is faster. Destruction of the previous community can occur due to forest fire, flooded lands, landslides, earthquakes, drought, overgrazed areas, storms, etc. Following such destruction, the process of succession will occur again from the new environmental conditions. It takes \(50-100\) years to complete a grassland and \(100-200\) years to develop a forest.

Fig: Primary and Secondary Succession

(c) Cyclic Succession: It is a pattern that takes place in an established community by changing the structure of the ecosystem on a cyclic basis.
(d) Autogenic Succession: After biotic succession has begun, the existing vegetation is held responsible for its own replacement by the new communities by changing the existing environmental condition. This succession is known as autogenic succession.
(e) Allogenic Succession: In allogenic succession, the existing community is replaced by other external conditions and not by existing vegetation itself.

Types of Successional Communities

There are three main types of successional communities: 
(a) Pioneer community is the one that sets first in a barren area. Examples include lichens on rock, phytoplankton and zooplanktons in ponds. They survive in the most hostile environment.
(b) Climax community is the last community in biotic succession, which is relatively stable and is in near equilibrium with the environment of that area called a climax community. Example: forests.
(c) Transitional or seral communities are the ones that follow the pioneer community. Examples include bryophytes, herbs, shrubs in xerosere, submerged, floating etc., in ponds. They contribute maximum to the formation of a stable community.
The entire series of communities occurring in biotic succession is called sere.
Seral stages or seral communities are individual transitional communities.

Seral community: It is an intermediate stage of ecological succession that advances towards the climax community. It consists of simple food chains and food webs.
The different types of seres are mentioned below:
(a) Xerosere or Xerarch succession –  When succession takes place in dry areas like a rock (lithosere), sand (psammosere) and saline conditions (halosere).

Fig: Xerosere or Xerarch Succession

(b) Hydrosere or Hydrarchsuccession – When succession starts on the aquatic habitat where water is plenty and progresses from hydric to mesic conditions.

Fig: Hydrosere or Hydrarch Succession

(c) Lithosere: This ecological succession develops on bare rock surfaces.
(d) Psammosere: This ecological succession originates on the sand.
(e) Halosere: The plant succession that begins on salty soil and saline water.
(f) Senile: This succession takes place on a dead matter of microorganisms.
(g) Eosere: It shows the development of vegetation in an era.

Stages of Ecological Succession

Clements \((1916)\) has discussed the process of ecological succession. This process involves the following stages, which are as follows:

1. Nudation: Development of bare area or nudation without any form of life. It may be caused due to several factors like volcanic eruptions, landslides, floods, erosion, earthquake, forest fire, the spread of disease, etc.
2. Invasion: It is the successful establishment of a species in a barren area. The arrival of reproductive bodies or propagules of various species and their settlement in the new or bare area occurs by air, water, etc., known as migration. Adjustment of establishing species with the prevailing conditions is known as ecesis. Then the individual species are multiplied by reproduction and increase their numbers; this is called aggregation.
3. Competition and coaction: After aggregation, the individuals of a species compete with other organisms for food, space and other resources. The intraspecific and interspecific competition takes place along with interaction with the environment. New invasion by plants and animals takes place.
4. Reaction: The modification of the environment through the influence of living organisms on it is called reaction.
5. Stabilisation (Climax): The stage at which the final or climax community becomes more or less stabilised for a longer time in that particular environment is known as stabilisation.

Examples of Ecological Succession

The examples of ecological succession are as follows:

a) The volcanic island of Surtsey is located off the coast of Iceland. In \(1963\), this island formed due to the eruptions of the volcano. After the eruption, the ground was primarily rocking. Fungi and mould started growing on the rock. These began to break down the rock to form soil. Then the small grasses begin to take root and start to grow. Following smaller shrubs begin to grow. The small burrowing animals moved in to disturb the soil as larger plants began to grow. After several years, trees begin to take root and grow where there was only rock.

b) Tropical forests are examples of secondary succession in which forests were cleared for timber and agricultural needs. In these areas, the reestablishment took place at varying speeds, and it took several years for a community to be fully restored.

Importance of Ecological Succession

The importance of ecological succession is as follows:

1. It shows the way of the sequence of biotic succession. Ecologists can immediately recognise the seral stage of a biotic community in an area.
2. It helps in knowing information about techniques to be used during reforestation and afforestation.
3. The knowledge of biotic succession is used to prevent the growth of superiors in an area and control the growth of one or more species.
4. Protection of dams by preventing siltation and occurrence of biotic succession.

Summary

Ecological succession is the gradual and predictable change in the species composition in an area over a while. It is a systematic process. It involves changes in species structure and also increases the diversity of species. The succession takes place due to changes in the physical environment and population of the species. The succession is mainly of two types: primary and secondary succession.

The ecological succession occurs in the five stages viz nudation, invasion, competition and coaction, reaction and stabilisation. It helps to recognise the seral stage of a biotic community in an area.

FAQs on Ecological Succession

Students might be having many questions regarding Ecological succession. Here are a few commonly asked questions and answers.

Q.1: What is ecological succession?
Ans: The gradual and predictable changes in the species composition of a given area are collectively called ecological succession.

Q.2: What are the five stages of ecological succession?
Ans: The five stages of ecological succession are nudation, invasion, competition and coaction, reaction and stabilisation (climax).

Q.3: What is primary succession?
Ans: Primary succession starts in a barren area, never having vegetation of any type where no living organism ever existed.

Q.4: What do you mean by halosere?
Ans: The plant succession that begins in salty or saline water is called halosere.

Q.5: What is the importance of ecological succession?
Ans: Ecological succession shows the way of the sequence of biotic succession. Ecologists can immediately recognise the seral stage of a biotic community in an area. Additionally, it helps in knowing information about techniques to be used during reforestation and afforestation.