What is Primary Succession?

Primary succession refers to a type or ecological succession that occurs in an environment that has just been formed, but does not have any habitable soil. However, living organisms are then colonized for their first time.

Primary succession refers to a series or events that occur in order to create a stable ecosystem. Natural events such as volcanoes or glacier eruptions that cause soil loss or absence of living organisms are often responsible for the formation of new environments. These organisms are called ‘pioneer species’. They are often made up of lichens, alga, and fungi. Primary succession is the weathering of rocks that forms soil to support the pioneer species. Primary succession can be initiated by either a biological or external factor.

After a certain amount of soil has been formed, organisms such as lichen, which have very low soil requirements, can grow in these areas. These organisms arrive in the new environment from another environment. These species also help to break down mineral-based rocks made of lava and glaciers. These pioneer species continue to reproduce, grow, die, and then decompose, creating soil pockets where other species can flourish. Decomposition of these organisms increases the soil’s organic content, which contributes to soil formation. This is repeated several times in each stage. Each stage is repeated several times. New species are introduced to the environment created by previous species. Some may even replace the former species.

These areas become home to fast-growing vegetation that covers most of the land. The seeds of large trees eventually reach the new environment via birds or wind, which attracts more animals. The stability of the ecosystem is achieved through primary succession. The ‘climax community’ is the community that reaches equilibrium in an ecosystem’s stable state. This point is much more stable than previous ecosystems in terms of composition and ecosystem. Primary succession can take years and is very slow. Primary succession can be described as the creation of a new ecosystem following a volcanic eruption, glacier outbursts or nuclear explosion.

Examples of primary succession

Primary succession after a nuclear explosion

It was assumed that there would be no human life in areas where nuclear bombs were tested. It was found that primary succession can begin even in these areas within 30 year. These areas are considered dead as there is no possibility of life for many years. All the radiation from a nuclear blast in the area has been eliminated after years.

Primary succession following nuclear explosion begins, just like in other situations, with weathering existing rocks. Pioneer species such as lichens or algae emerge from the rocks, which causes them to begin to fall apart. This results in the first groups of living organisms appearing. The process of succession continues and a new group replaces the old ones, leading to an increase in organic matter. The area is now home to a stable climax or ecosystem after 100 years.

Primary succession in sand dunes

The harsh environment of seashores is caused by high winds, moving sand and low nutrients. This environment lacks stable ecosystems, and pioneer organisms such as bacteria can live in a symbiotic relationship to pioneer plants. These plants have root systems that allow them to anchor to shifting sand. They also have numerous modifications to prevent water loss and lack of organic matter.

The lichens, which are organic matter that is deposited on large stones along the shore, then follow these grasses. The environment grows and new species replace the living organisms until it reaches a stable climax. In the end, organisms that can survive in high salt concentrations eventually live in dunes or on seashores.

What is Secondary succession?

Secondary succession refers to a type or ecological succession that occurs when an ecosystem is damaged by an event such as fire or hurricane, and then is re-colonized again by other organisms.

Secondary succession is not like primary succession. It begins in an environment that has pre-existing soil. Secondary succession occurs in an environment that has experienced disruptions to the original succession, although some plants or animals may still be present. This type of succession is usually triggered by natural disasters such as a hurricane or forest fire. Secondary succession is always initiated by external factors. The tall trees are destroyed by a forest fire. In such areas, the first plants to grow are often annual plants.

These annual plants include grasses, low-lying plants, and other pioneer species. Like primary succession, the pioneer species are also known as early colonizers. These pioneer species are not like those in primary succession. They mostly emerge from pre-existing communities of organisms. Changes in the environment due to the growth and development of grasses can lead to new species such as shrubs or herbs. These organisms are known as intermediate species, which can further alter the environment and facilitate the growth of taller plants.

Over a long time, the environment’s composition changes back to its pre-fire state. Many factors affect the succession process, including seed dispersal as well as seed production. Other factors such as climate, pH, bulk density and soil texture also influence the composition of the community and their interactions. The nature of the community formed after secondary succession depends on the trophic interaction, the initial composition of the environment, and the competition-colonization processes.

Secondary succession takes less time than primary succession. For example, secondary succession after a forest fire can take around 150 years. Secondary succession can be described as succession after fire, harvesting or logging or abandonment of land, or the revival after a disease outbreak.

Examples of secondary succession

Harvesting, logging, and abandonment of land

Human-induced secondary succession is evident in the abandonment of cropland. As nutrients are constantly removed from cultivated land, it is more common for the soil to become deficient in nutrients. Lack of organic matter can make it difficult for plants and other organisms to grow. Secondary succession starts with the establishment pioneer vegetation after the land has been abandoned. These areas are rich in organic matter and nutrients that allow for the growth of newer organisms.

The vegetation is then replaced with shrubs and herbs, which act as natural disaster barriers against soil erosion. As new communities form, the cropland becomes fertile again. The soil type and artificial fertilizers used to these land may make secondary succession different in human-affected landscapes. This results in specialist plants being introduced to the area, which decreases biodiversity.

Renewal after diseases

Secondary succession can also occur in areas where an existing ecosystem has been destroyed by disease. A disease can be fatal for one species but it can also affect other species in the ecosystem. The roots and seeds of certain plants may still be present in the soil, which could lead to secondary succession. The removal of one species could allow for the colonization of another species that might have been competing with the colonizers. This condition allows for secondary succession, which can allow biodiversity in an environment where new and diverse groups of organisms may inhabit it.

Difference between Primary and Secondary Succession – Primary vs Secondary Succession

Basis for Comparison	Primary succession	Secondary succession
Definition	Primary succession refers to a type or ecological succession that occurs in an environment that has just been formed, but does not have any habitable soil. However, living organisms are then colonized for their first time.	Secondary succession refers to a type or ecological succession that occurs when an ecosystem is damaged by an event such as fire or hurricane, and then is re-colonized again by other organisms.
Initial vegetation	Primary succession is the process of removing all vegetation from an area.	Secondary succession can occur in areas with initial vegetation.
Initiation	Primary succession can be initiated by a biological factor, or an external agent.	Secondary succession can be initiated by an external factor.
Soil	The area is devoid of any surface soil before the first step in primary succession.	Secondary succession can occur in areas that are not covered by surface soil.
Organic matter	Primary succession is not possible without organic matter.	Secondary succession is a process in which organic matter is found in the environment.
Environment	Primary succession has a hostile environment, but it becomes more favorable as new species grow.	From the beginning, the environment is favorable.
Pioneer species	The ecosystem is populated by the pioneer species of primary succession.	These are the species that were present in the original ecosystem and are considered the pioneer species of secondary succession.
Primarily, lichens are the pioneer species in primary succession. Then come algae and fungi.	Grasses are the most common pioneer species in secondary succession.
Intermediate community	During primary succession, many intermediate communities are created.	Secondary succession results in fewer intermediate communities.
Previous community	Prior to primary succession, there was no previous community.	The environment is home to the remnants of previous communities that existed before secondary succession.
Time	Primary succession can take longer to complete.	Secondary succession is quicker to complete.
Examples	Primary succession can be described as the creation of a new ecosystem following a volcanic eruption, glacier outbursts or nuclear explosion.	Secondary succession can be described as succession after fire, harvesting or logging or abandonment of land, or the renewal of land after a disease outbreak.