Difference Between Primary & Secondary Succession

Now, there are multiple ecological systems that exist, including environmental ecology, landscape ecology, and many more. Our focus here should be on ecological succession and its types and mechanisms and nothing else. So, succession means a follow-up or a series of things that follow after one another and so on. Therefore, ecological succession would mean an elaborate process of extended relationship of ecological systems with other things in the environment.

According to E.P. Odum (1971), “the ecological succession is an orderly process of community change in a unity area”. It is the process of changes in species composition in an ecosystem over time. 

Before understanding the primary and secondary succession, it is important to understand the causes of succession. 

Causes of Succession 

Since succession is a process, more appropriately, a series of complex processes, it is natural that there may not be a single cause for this. There are three types of cause: 

i) Initial or initiating cause can be  climatic as well as biotic. The initial cause includes factors such as erosion and deposits, wind, fire, etc., caused by lightning or volcanic activity, and the latter includes the various activities of organisms. Succession is responsible for bare areas or destroying the existing populations.

ii) Continuing causes involve processes such as migration, esesis, aggregation, competition, reaction, etc., which result in changes, chiefly in edaphic features of the area.

iii) Stabilising causes result in the stabilisation of the community. Clements describes it as “the climate of the area is the chief of stabilisation, other factors are of secondary value”. It can be said that the final terminal community becomes more or less stabilised for a longer period of time, which can also be called the climax community.

What is Ecological Succession?

Ecological succession can also be called plant succession or biotic succession. The term “succession” was first given by Hult in 1885, and the authentic studies on succession were started in America by Cowles in (1899) and Clements in (1907). Ecological succession is considered important because it allows new areas to be colonised and damaged ecosystems to be recolonised, and in this order, the organisms can adapt to the changes in the environment and continue to survive and live in that environment. It is an adaptive behaviour technique in the ecosystem by which the damaged parts are replenished so that they can further be alive and grow in the environment.

The process of evolution of the structure of the biological species is known as ecological succession. It is the process of change in the species structure of a community in an ecosystem over a while. The time scale is usually long, which may range from decades, or natural destruction, for example, after a wildfire, or even millions of years after a mass extinction. The cause of ecosystem change or what fuels ecological succession is the impact that the established species make upon their environments.

Characteristics of Ecological Succession

Thus, succession is the order of colonisation of species in an ecosystem from a barren or destroyed area of land and the one from already inhabited lands.

Ecological succession is the steady and gradual change in a species of a given area of land. This change occurs concerning the changing environment of that particular ecosystem. It is a predictable and inevitable process of nature as all the biotic components have to keep up with the changes in the environment.

It takes place until an equilibrium is reached in the ecosystem and the community that achieves it is called the climax community.

The sequence of changing communities over a period is called sere and each community that arrives in the process is called a seral community.

It is a part of nature right from the Earth’s existence. Therefore, it is the process that takes place simultaneously along with evolution.

Primary succession is a slower process than secondary succession. Because, life has to start from a zero, whereas secondary starts at a place that had already supported life before.

Types of Ecological Succession

An ecological succession is initiated either by the formation of new, unoccupied habitat, such as from a lava flow or a severe landslide, or by some form of disturbance of a community, such as from a wildfire, severe windthrow, or logging, which may wipe out the entire species. Thus, succession is of two types:

• Primary Succession - Succession that begins in new habitats or lifeless areas that are uninfluenced by pre-existing communities is called primary succession. Primary succession starts from a barren land, such as open water, where the newly formed rock is colonised for the first time, such as formation of a new ecosystem after a volcanic eruption or glacier breakage. It can be a lengthy process because of the time taken by the natural calamities to occur, which in itself is a rare occasion. So the process is slightly longer and unpredictable for the entire course of time.

• Secondary Succession - Succession that follows the disruption of a pre-existing community that existed in the same ecosystem is called secondary succession.

Secondary succession is  a more deliberate and elaborate process because it involves the destruction of the primary ecosystem. Now it might sound tricky, but the explanation settles it. For example, there is a pre-existing ecosystem, and then somebody comes and destroys it, like if you own a land and you have planted trees, and now if someone comes and destroys it or if you give it to someone and that person decides to destroy it to make a multiplex, then that can be described as a secondary succession. The occurrence of secondary succession can be seen in its action when the primary ecosystem gets destroyed by another agent. It gets recolonised after the destruction.  This can be identified as secondary succession.

Primary Succession

Primary succession is the type of ecological succession that starts in lifeless areas. It is the one in which plants and animals first colonise a barren, lifeless habitat, such as the regions devoid of soil or the areas where the soil is unable to sustain life. The pioneer species or the first species build an initial biological community that is simpler in form. This community gradually becomes more complex with the arrival of new species.

When the planet was first formed, it was just a mere sphere of gases with the absence of soil. It evolved to contain only rocks in place of soil. These rocks were eroded by physical conditions and broken down by microorganisms to form soil. The soil then became the primary foundation of plant life. Various animal species adapted to survive on plants. Thus, it progressed gradually from primary succession to the climax community. 

Secondary Succession

The secondary is the second type of ecological succession that occurs when the primary ecosystem gets destroyed. Thus, it is the type of succession in which plants and animals recolonise a habitat after a major disturbance like a landslide, lava flow, wildfire, etc. It occurs when a climax community gets destroyed. Secondary succession takes place in an ecosystem where the disturbance did not eliminate all life forms and nutrients from the environment. Small plants emerge, followed by larger plants at the beginning of the succession. They develop into tall trees that block the sunlight and change the structure of the organisms below the canopy. By the end of all this, the climax community arrives.

Mostly insects and weedy plants are the first organisms to recolonise in secondary succession. Gradually, more complex and stable species of plants and animals arrive. Stability in the ecological structure of a biological community is established when the area remains undisturbed for a long period.

What are the differences between Primary & Secondary Succession