Ecological Succession, Definition, Diagram, Types, Stages, Causes

Ecological succession is the gradual, directional change in the species composition of ecosystems over time. It begins in a bare area with pioneer species and progresses through seral communities until reaching a stable climax community. Succession can be primary, starting in lifeless areas, or secondary, following disturbances like wildfires or deforestation. Other types include autogenic, allogenic, progressive, and retrogressive succession.

This natural process is crucial for restoring ecological balance, supporting biodiversity, and creating self-sustaining ecosystems. Examples like coral reefs, tropical forests, and Acadia National Park show nature’s resilience and its ability to recover and thrive after disturbances.

Ecological Succession Definition 

Ecological succession is the gradual, directional change in the species composition of a community over time, driven by processes where communities modify the physical environment. This leads to the development of more stable, mature, and self-maintaining ecosystems.

Key Features

Ecological succession involves changes in a community’s structure and function over time. It follows a predictable, directional process, transitioning from unstable to stable, self-maintaining ecosystems. This process typically spans 1 to 500 years.

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Ecological Succession Terminologies

Succession starts in a bare area with a pioneer community and progresses through seral communities, eventually forming a stable climax community. Each stage involves directional changes until the ecosystem reaches maturity. These are explained below in detail: 

• Bare area: Habitat without any vegetation from where succession starts. Wholly independent of the structural, nutritional aspects of their soil, bare areas may be classified into the following three categories according to their characteristic water relations:
  • Wet or hydric (e.g. pond bottom); Dry or xeric (e.g. rock surface exposed to the sun); Intermediate or mesic.
• Pioneer Community: Succession starts with a community by establishing first in any bare area.
• Sere: A whole sequence of communities that replace one another in a given area i.e. the entire progression of seral stages from the first one to occupy a bare area to the climax community. 
• Successional or Seral community: The relatively transitory communities or developmental stages that develop during succession and exhibit some directional, cumulative, nonrandom change in 1 – 500 years, until a climax community is achieved.
• Climax Community: Succession ends with a community in which the species perpetuate themselves through reproduction till the climate remains the same. 

Ecological Succession Diagram

Ecological succession is the natural, gradual process through which ecosystems develop, starting from exposed rock with pioneer species like lichen and mosses, progressing through stages with annual wildflowers, and shrubs, and eventually reaching a stable climax community. The sequence is  illustrated in the diagram below:

Ecological Succession Types

Ecological succession is the gradual change in species composition, including primary, secondary, autogenic, allogenic, progressive, retrogressive, directional, and cyclic succession, driven by various factors. These are given below in detail:

• Primary Succession: Involves the establishment of vegetation on land not previously vegetated. If it begins on a wetland (pond, lake), it’s called hydrarch succession; if on dry land (sand dunes, rocks), it’s xerarch succession.
• Secondary Succession: Occurs in areas that were previously vegetated but disturbed by natural disasters or human activities. Soil remains, often allowing quicker vegetation recovery.
• Autogenic Succession: Changes in species composition are driven by the organisms themselves, altering their environment through factors like shade or litter accumulation.
• Allogenic Succession: Environmental changes are caused by external forces beyond the control of the local organisms, such as storms or fires.
• Progressive Succession: This leads to more complex communities with greater biomass and a more mesic (moist) habitat.
• Retrogressive Succession: Results in species loss and reduced complexity, leading to either more hydric (wet) or xeric (dry) habitats, driven by factors like cattle grazing or invasive species.
• Directional Succession: Refers to cumulative changes in a community over time, leading to widespread ecological shifts.
• Cyclic Succession: Involves non-directional, repeating cycles of local changes in the community.

Ecological Succession Primary

Primary succession is the process by which an ecosystem develops in a previously barren area, such as a newly formed volcanic island. After the rock cools, wind-blown seeds lodge in crevices, allowing fast-growing pioneer species like grasses to take root. These early plants decompose, forming the first pockets of soil.

• As more plants grow and the soil deepens, new species arrive, often brought by birds. Taller plants begin to dominate, shading out the early colonizers. 
• Over time, animals also arrive, and the ecosystem gradually becomes more complex and stable, completing the succession process.

Ecological Succession Secondary

Secondary succession occurs after a major disturbance, such as a wildfire, flood, or human activity, wipes out part of a landscape. The process is similar to primary succession, with insects and weedy plants first recolonizing the area, followed by hardier species over time. If undisturbed, the ecosystem can eventually regain stability.

• Although disturbances can devastate landscapes, the soil often retains seeds that sprout after the event, allowing recovery through secondary succession. 
• However, severe disturbances like volcanic eruptions or glaciers can destroy biological activity entirely, requiring primary succession for the ecosystem to redevelop.

Ecological Succession Stages

Ecological succession is the gradual process of community development in a previously barren or disturbed area. It involves key stages such as nudation, invasion, competition, reaction, and the establishment of a stable climax community. These are explained below in detail:

• Nudation: The process starts with the development of a bare area without life, exposed by factors like landslides, erosion, volcanic activity, or human intervention. The causes of nudation can be topographic, climatic, or biotic. This leads to the formation of soil. 
• Invasion: After the bare area is exposed, species begin to colonize the new site. This involves three steps:
  • Migration: Seeds or spores disperse to the area through air, water, etc.
  • Ecesis: The species adjust to the environment, establishing a foothold and starting full colonization.
  • Aggregation: Reproduction increases the population, and pioneer species (the first colonizers) begin to thrive.
• Competition and Coaction: As the population grows, competition for space and resources intensifies. Species influence each other’s survival, and weaker competitors are eventually displaced.
• Reaction: Organisms alter the environment (soil, water, temperature) through their activities. These changes make the area less suitable for the existing community, leading to its replacement by a new community, known as a seral community.
• Stabilization (Climax): Eventually, a stable community develops, reaching a balance with the climate and environment. This climax community remains largely unchanged for a long period, marking the final stage of succession.

Ecological Succession Causes

Ecological succession is driven by a variety of factors that can be classified into three major types: initiating causes, continuing causes, and stabilizing causes. Each plays a crucial role in the development and stabilization of ecological communities over time.

• Initial/Initiating causes: These are climatic as well as biotic. The factors include erosion and deposition, wind, fire, activities of organisms, etc. These causes produce the bare areas or destroy the existing population in the area. 
• Ecesis/Continuing causes: These are the processes such as migration, ecesis, aggregation, competition, reaction, etc., which cause successive waves of populations as a result of changes, chiefly in the edaphic features of the area.
• Stabilizing causes: These cause the stabilization of the community. According to Clements, the climate of the area is the chief cause of stabilization, other factors are of secondary value.

Ecological Succession Example 

Ecological succession occurs in various natural environments, showcasing how ecosystems recover and evolve. From coral reefs to tropical forests and even after disturbances like wildfires, different types of succession demonstrate nature’s resilience. These are explained below in detail:

• Coral Reefs: Small coral formations settle on rocks, growing into larger colonies. This attracts small fish, eventually creating a thriving coral reef ecosystem.
• Tropical Forests: After deforestation, secondary succession occurs as forests regrow, taking years to restore a fully functioning community.
• Acadia National Park: After a wildfire, small plants grew on burned soil. Over time, the forest transitioned from mostly evergreen trees to a mix of deciduous species.

Ecological Succession in Ecosystem

Ecological succession is a continuous process through which ecosystems recover and evolve after disturbances, whether through primary succession in barren landscapes or secondary succession following disruptions. Each stage contributes to the restoration of ecological balance, supporting biodiversity and the gradual development of stable ecosystems.

Ecological Succession  UPSC PYQ 

Q1. In the grasslands, trees do not replace the grasses as a part of an ecological succession because of (UPSC Prelims 2013)

(a) insects and fungi

(b) limited sunlight and paucity of nutrients

(c) water limits and fire

(d) None of the above

Ans. (c)

Q2. Which one of the following is the correct sequence of ecosystems in the order of decreasing productivity? (UPSC Prelims 2013)

(a) Oceans, lakes, grasslands, mangroves

(b) Mangroves, oceans, grasslands, lakes

(c) Mangroves, grasslands, lakes, oceans

(d) Oceans, mangroves, lakes, grasslands

Ans. (c)

Q3. Which one of the following terms describes not only the physical space occupied by an organism but also its functional role in the community of organisms? (UPSC Prelims 2013)

(a) Ecotone

(b) Ecological niche

(c) Habitat

(d) Home range

Ans. (b)