“The orderly changes in community structure and function in an ecosystem with time mediated through the modifications in the physical environment ultimately leading to a stable community over that area.”
The process of Ecological Succession is a systematic progression of changes in the species structure and function within a community over time. This process is both continuous and directional, making it predictable.
This natural phenomenon arises from modifications in the physical environment by the community's species. These changes result from ongoing competition among species for essential physical factors such as light and space, as well as resources like energy and nutrients. Despite the community's influence, the modifications in the physical environment play a crucial role in determining the patterns, rates of change, and overall development during the succession process.
The ultimate outcome of ecological succession is the establishment of a stable ecosystem featuring a dominant species, known as the climax species. This climax species achieves a state of equilibrium with the surrounding environment.
The entire sequence of communities that successively replace one another in a specific area is termed a "sere," and the intermediary communities are referred to as "seral stages." These stages include the grass stage, herb stage, shrub stage, etc. The initial phase is labeled the pioneer stage, characterized by an early successive pioneer plant community. The last or terminal stage is recognized as the climax. The pioneer community is more easily replaced by the next seral stage, while the climax community is considered a more mature and stabilized stage within the ecosystem.
On the basis of nutrient availability, succession are of two types : primary and secondary succession.
Primary succession initiates in newly formed areas characterized by elementary environmental conditions, such as a bare expanse resulting from phenomena like lava flow, landslides forming new ponds, sand dune formation, or the exposure of rock surfaces due to retreating glaciers. In these pristine areas, there is an absence of any biological legacy, including vegetation, seed banks, or organic matter. Initially unoccupied by any community, the introduction of the first organisms depends on immigration, as there are no existing seeds or propagules.
Example of primary succession :
Barren land devoid of soil and succession begins with pioneer species like lichens and mosses colonizing the volcanic rock. These resilient organisms thrive in harsh conditions, breaking down the rock and contributing to soil development. Over time, as soil accumulates, more advanced plants such as ferns and grasses take root. The ecosystem evolves further, with shrubs and trees eventually establishing themselves, resulting in a diverse and mature community.
Secondary succession commences in an area that was previously inhabited by a community but has been stripped of vegetation due to various natural or human-induced activities such as fire, storms, tree cutting, disease outbreaks, cultivation, or other biotic interventions. Over the course of several years, a new community begins to reclaim and occupy the area, marking the onset of secondary succession. Although the region may lack visible living matter above ground, its substratum is enriched with nutrients, organic matter, or propagules left behind by the prior community. Unlike primary succession, secondary succession is characterized by a more rapid process of ecosystem recovery.
Example of secondary succession :
After a forest fire, secondary succession occurs as the scorched landscape undergoes renewal. Pioneer species, including grasses and herbaceous plants, swiftly colonize the barren soil, stabilizing it and initiating the recovery process. As these early plants establish, they create conditions conducive to the growth of more complex vegetation, such as shrubs and young trees.
Sere : the entire sequence of communities that successively change in a given area is called sere. The name of sere depends on where the succession occurs or takes place. Different types of seres are as follows :
(Session 2026 - 27)