Ecological Succession is the gradual process by which ecosystems change and develop over time, often following a disturbance. This dynamic process can be observed in various real-life scenarios around the world. For example, after a forest fire, hardy species adapted to survive fires are the first to regrow, gradually replaced by larger shrub and tree species until the forest is restored. In urban settings, even abandoned buildings can become habitats, initially colonized by lichens and certain hardy plants, ultimately leading to a unique urban ecosystem. After a volcanic eruption, the barren landscape undergoes primary succession, starting with lichens and mosses and eventually leading to a full-fledged ecosystem. From recapturing farmland to the restoration of wetlands, ecological succession demonstrates nature’s resilience and the intricate balance within ecosystems.

Ecological Succession

Ecological succession is the process through which ecosystems undergo natural changes over time due to environmental disturbances. This progression is marked by distinct stages, each characterized by a unique community of plants and animals. Succession can be primary, occurring on previously uninhabited areas like lava flows or bare rocks, beginning with colonization by organisms like lichens or mosses. Alternatively, it can be secondary, occurring in areas where an existing ecosystem has been disturbed or destroyed, such as after forest fires or hurricanes. Over time, these ecosystems evolve from a simple level of species diversity to a more complex community. The final stage, known as a climax community, is a stable and mature ecosystem that is in balance with the surrounding environment. Through succession, nature showcases its ability to recover and regenerate, illustrating its resilience and dynamism.

Types of Ecological Succession

Ecological succession is categorized into two main types: primary succession and secondary succession.

• Primary Succession

This is the series of community changes which occur on an entirely new habitat that has never been colonized before. The new habitat could be a bare rock, newly formed sand dunes, or a new pond. It starts with colonization by pioneer species, which are hardy organisms (often lichens and mosses) that are first to colonize the previously disrupted or damaged ecosystem. These pioneer species start the process of soil formation, allowing other, more complex plants and animal species to establish over time. The end result of primary succession is a stable, mature community known as a climax community.

• Secondary Succession

This type of succession occurs on sites where a biological community has already existed but some disturbance (like a fire, flood, or human activity) disrupts and sets back the successional process. Unlike primary succession, secondary succession happens much faster because it occurs in areas where the soil or sediment is already present, allowing life to return more quickly.

In some ecosystems, a stable climax community is never reached. These ecosystems experience cyclical changes driven by disturbances. This type of succession is often referred to as Cyclic or Seasonal Succession.

Some researchers also talk about Retrogressive Succession, which is a pattern of change characterized by the gradual transition from high biomass and nutrient-rich conditions towards lower biomass and less fertile conditions. This type of succession is common in areas where soil nutrients are low or where disturbances are frequent.

Understanding these different types of succession provides important insight into how ecosystems recover from disturbances and how species coexist over time.

Seral Community

A seral community (or sere) is an intermediate stage found in ecological succession in an ecosystem advancing towards its climax community. A seral community is not stable or final, but rather, it is transitory. It progresses from smaller, simpler species of plants and animals to larger, more complex ones, until the ecosystem reaches its final stage of succession, known as the climax community.

In primary succession, the first seral stage is typically dominated by pioneer species, which are often hardy species capable of surviving in harsh conditions. These pioneer species help to create more hospitable conditions and modify the environment in ways that enable other species to colonize the area.

Subsequent seral stages are usually characterized by more complex and diverse groups of plants and animals. Over time, these seral communities transition towards the climax community, which is the final and stable stage of succession, characterized by a mature, diverse, and complex community of organisms.

Each seral community makes the conditions more favorable for the next stage of succession but less favorable for its own maintenance, leading to its replacement by the next seral stage. The specific sequence and composition of seral communities can vary depending on the region, climate, and specific environmental factors.

Here’s a simplified example that shows the progression from bare substrate to climax community:

Seral Stage	Dominant Life Forms	Description
Bare Substrate	None	This is the initial stage following a disturbance, such as a volcanic eruption or glacier retreat. The environment is reduced to bare rock or sand with no life.
Pioneer Community	Lichens, mosses	The first colonizers are hardy pioneer species, often lichens or mosses, that can survive harsh conditions and begin to break down the substrate.
Annual Herb Stage	Fast-growing annual plants	As the soil begins to form, annual plants take root. These plants grow quickly, produce many seeds, and die within a year.
Perennial Herb and Grass Stage	Perennial plants, grasses	Over time, slower-growing but longer-lived perennial plants and grasses start to dominate. They add more organic material to the soil.
Shrub Stage	Shrubs	As the soil becomes even richer, shrubs start to grow. They provide shade and change the local environment in ways that make it less suitable for the earlier species.
Young Forest Stage	Young trees	As conditions become even more hospitable, tree seedlings start to grow. These trees eventually grow taller than the shrubs and start to form a young forest.
Mature Forest/Climax Community	Mature, long-lived tree species	Finally, the forest matures into a stable, self-sustaining ecosystem. This is known as the climax community, which remains relatively unchanged until disrupted by another disturbance.

Causes of Ecological Succession

Succession is typically triggered by a disturbance or a significant change in an environment that makes it habitable for different types of organisms.

The causes of succession can be grouped into two main categories:

• Natural Causes

• Climatic Changes

Changes in climate, including shifts in temperature, precipitation, or seasonal patterns, can lead to changes in the types of organisms that can survive in a particular ecosystem.

• Natural Disasters

Events like fires, floods, hurricanes, landslides, or volcanic eruptions can cause significant disturbances to an ecosystem, clearing the way for new organisms to colonize the area.

• Biological Processes

Activities of organisms themselves can lead to changes in the ecosystem. For example, the overgrazing by animals can expose bare soil allowing different plant species to take root. Predators can control prey population, influencing the balance of species in an ecosystem.

• Anthropogenic (Human-induced) Causes

• Agricultural Practices

Human activities like farming can lead to changes in the ecosystem. For example, when a field is left fallow, secondary succession occurs as native plant species re-colonize the area.

• Urbanization and Industrialization

Construction, pollution, and other forms of habitat alteration due to urban development or industrial activities can lead to changes in the species that can survive in an area.

• Deforestation

The clearing of forests can disturb the existing ecosystem, allowing different species to colonize the area.

• Reclamation Projects

Efforts to restore disturbed lands, such as reforestation projects or wetland restoration efforts, can initiate succession as new species colonize the area.

In each of these cases, the initial disturbance creates an opportunity for new species to establish themselves, beginning the process of succession. Over time, as conditions change due to the influence of the organisms living there, different species become dominant, leading to a succession of different communities.

Examples of Ecological Succession in Real Life

• After a Wildfire

In forests that have been destroyed by wildfires, grasses are usually the first species to appear. Their roots help stabilize the soil and they grow quickly in the newly available sunlight. These grasses are then followed by shrubs and tree seedlings, and eventually, a mature forest develops.

• After a Volcanic Eruption

After a volcanic eruption, the landscape can be covered with a layer of ash. Pioneer species like mosses and lichens are the first to colonize this barren landscape. These organisms break down the ash and begin to form soil. Once enough soil is present, grasses can take root, followed by shrubs, and then trees. This process can be observed at places like Mount St. Helens in Washington, USA.

• Abandoned Agricultural Fields

When farmland is abandoned, the field is first colonized by weedy annual plants, which are replaced by perennial herbs and grasses after a few years. Shrubs will start to appear a decade or so after abandonment, and eventually, trees will begin to grow, leading to a young forest. This is known as old-field succession.

• Sand Dunes Succession

This can be observed in coastal regions. The pioneer species in this case are often grasses adapted to survive in the harsh conditions of the beach, like marram grass. These grasses stabilize the sand and create conditions that allow other plants, like shrubs and trees, to grow. Over time, the sand dune can transform into a fully developed forest.

• After Glacier Retreat

When a glacier retreats, it leaves behind bare rock. Pioneer species, like mosses and lichens, colonize the rock and start to break it down, forming soil. Once enough soil is formed, grasses and then shrubs can grow. Eventually, a forest may form. This process is currently being observed in areas like Glacier Bay, Alaska.

• Recovery after Human Disturbance

This could involve areas that have been heavily logged or mined. After the human disturbance ends, pioneer species start to colonize. Over time, if left undisturbed, the area can eventually return to a state similar to its original condition. The exact process can vary widely depending on the specific conditions of the site.

• Pond Succession

Over time, a pond can slowly fill with sediments and organic matter, turning into a bog or marsh, and eventually a terrestrial habitat. This process begins with algae and other small aquatic plants. Over time, the pond becomes shallower due to the accumulation of plant material and sediments, allowing for the colonization by larger aquatic plants, like lily pads. As the pond continues to fill, it turns into a marsh or bog, dominated by reeds and grasses. Finally, the marsh can fill in completely, allowing for the growth of trees and the creation of a forest.

• Coral Reef Succession

In case of destruction (due to events like storms, disease, or human activity), coral reefs can recover through a process of ecological succession. Initially, algae and soft corals begin to colonize the vacant reef substrate. Over time, hard corals start to grow, eventually forming a complex and diverse coral reef system. The exact process can vary significantly, depending on the severity of the damage, the specific species present, and other local conditions.

• After Landslides

Landslides, by stripping off vegetation and surface soil layers, can initiate a process of ecological succession. This process starts with the colonization by hardy pioneer plant species, typically certain types of grasses and herbs, followed by the establishment of shrubs, and eventually the return of trees and a fully functioning forest ecosystem. This process can take many decades or even centuries, depending on the severity of the landslide and local conditions.

• Urban Succession

This can happen in abandoned human structures or urban environments. The first species to colonize are typically hardy plants like grasses, weeds, or even trees that take root in cracks in the pavement or bricks. Over time, these plants can break down human structures, creating pockets of soil where other plants can grow. Animals, such as insects, birds, and small mammals, also start to inhabit these areas. Over time, if left undisturbed, an entire ecosystem can develop.

• After Tsunamis

Tsunamis can cause massive destruction to coastal ecosystems. After a tsunami, the land can be left in a state similar to primary succession, where the land is virtually bare. Pioneer species like grasses, and then shrubs, colonize the land first. Over time, if the area is left undisturbed, it can eventually recover into a mature ecosystem.

• Mine Spoil Heaps

Mining often leads to large piles of waste rock or spoil. Over time, hardy pioneer species, often grasses and other plants adapted to harsh conditions, can colonize these piles. These plants help stabilize the spoil heap and start to create soil. Over time, a diverse community of plants and animals can establish, transforming the spoil heap into a new habitat.

• Landfill Sites

Once a landfill site is closed, it can be capped and then revegetated. The first plants to grow are usually grasses and other fast-growing species, which help stabilize the soil. Over time, a diverse community of plants and animals can establish, transforming the landfill site into a new habitat.

• Roof Tops and Walls

Even in urban areas, plants can colonize cracks in buildings or flat roofs. These plants are typically well adapted to harsh conditions, such as drought and heat. Over time, these plants can create pockets of soil and more diverse communities can establish.

• Secondary Succession in Tropical Rainforests

After a disturbance like logging or a smaller-scale natural disaster, the first species to recolonize are usually fast-growing “pioneer” trees that are adapted to survive in the high levels of sunlight that reach the forest floor. As these trees grow and create shade, slower-growing species start to establish underneath them. Over time, the pioneer species are replaced by a diverse community of shade-tolerant trees and the forest returns to a similar state as before the disturbance.

• Lakes and Rivers After Pollution Events

When a water body is heavily polluted, many species may die off. After the pollution is cleared, the water body can recover through a process of succession. The first species to colonize are usually fast-growing algae and bacteria. These species start to oxygenate the water and create conditions that allow other species to colonize. Over time, if left undisturbed, the water body can return to a state similar to its original condition.

• After an Avalanche

Avalanches can destroy vegetation, particularly in mountain ecosystems, leaving bare ground in their wake. The recovery process often begins with the establishment of pioneer species like mosses, lichens, and grasses. Gradually, shrubs and then trees follow, until a mature forest ecosystem reestablishes over many years.

• After Floods

Floods can change the landscape drastically by eroding soil and washing away vegetation. After the water subsides, the process of succession begins. Pioneer species like grasses emerge first, followed by larger plants, and eventually trees, given the area is conducive for their growth.

• After Droughts

In areas where prolonged droughts have led to the death of vegetation, hardy pioneer species that are resistant to drought are the first to recolonize once rainfall returns. Over time, more diverse plant communities establish as the soil improves, leading to the return of animals and a fully functioning ecosystem.

• Coastal Succession after a Hurricane or Typhoon

These events can cause significant damage to coastal ecosystems. After such a disturbance, the bare sand will initially be colonized by hardy, salt-tolerant grasses and plants. Over time, these pioneers will stabilize the dunes and enable other plants and then trees to grow, leading to a complex coastal ecosystem.

• Fallen Tree in a Forest

When a large tree falls in a forest, it creates a gap in the canopy, letting in sunlight. This gap is quickly colonized by fast-growing “pioneer” species that take advantage of the sunlight. Over time, slower-growing, shade-tolerant trees begin to grow and eventually overtake the pioneers, closing the gap in the canopy.

• Thermal Springs and Geysers

In these extreme conditions, thermophilic bacteria and archaea, which can tolerate high temperatures, colonize first. These microbes form mats or biofilms and begin the process of succession. Over time, other microorganisms can colonize the area, creating a diverse microbial ecosystem.

• After a Nuclear Disaster

In areas impacted by a nuclear disaster, like Chernobyl, the immediate aftermath saw a reduction in biodiversity. However, over time, nature has started to reclaim the area, with wildlife and vegetation returning, even in the face of radiation.

• Invasive Species Impact

When an invasive species is introduced to a new area, it can significantly disrupt the existing ecosystem, leading to a form of succession as the ecosystem adjusts. When the invasive species is controlled or eradicated, the recovery of the original ecosystem can be viewed as a process of ecological succession.

• After an Oil Spill

In the aftermath of an oil spill, the impacted area can be dramatically affected, leading to the death of many organisms. Once the oil is removed or degraded, pioneer species begin to return. Over time, the ecosystem may gradually recover through a succession process, although the speed and extent of this recovery can depend on many factors, including the scale of the spill and the cleanup efforts.

• Restoration Ecology Projects

In many cases, humans actively attempt to restore damaged ecosystems, such as wetlands, forests, and prairies. These restoration efforts often involve planting a variety of native species and controlling invasive ones. Over time, the area can recover through a process of planned ecological succession.

• Man-Made Structures

Over time, abandoned buildings, bridges, or other man-made structures can become colonized by plants and animals. The process begins with pioneer species such as lichens and certain hardy plants, which can grow in the harsh conditions of a concrete or brick surface. Over time, these pioneers can create conditions that allow for a more diverse community of plants and animals to establish, ultimately leading to a unique urban ecosystem.

• Succession in the Intertidal Zone

Changes in the intertidal community composition can occur after disturbances like storms or human impacts. The first species to recolonize are often hardy, fast-growing species like certain types of seaweed or mollusks. Over time, a diverse intertidal community can reestablish.

• Succession in Space

On the International Space Station, where humans have introduced microorganisms, the composition of microbial communities can change over time, reflecting a form of succession. The microbes that are best suited to the space environment become more prevalent as the less adapted species die off.

• After an Earthquake

Major earthquakes can drastically alter landscapes and ecosystems. Land may be uplifted or sunk, rivers can change their course, and forests can be leveled. In the aftermath, succession processes begin, starting with pioneer species that colonize the disturbed areas. Over time, a new stable ecosystem can develop, although it may be different from the original one due to the significant landscape changes.

• Lichens on Bare Rock

One of the classic examples of primary succession begins with lichens colonizing bare rock. Lichens, which are a symbiotic association between fungi and algae or cyanobacteria, can endure the harsh conditions of bare rock and start the process of soil formation by breaking down the rock. This eventually leads to the development of more complex ecosystems.

• Mangrove Succession

In coastal areas, the first stage of succession often involves the establishment of pioneer mangrove species that are tolerant of high salinity and waterlogged conditions. These mangroves trap sediment and gradually build up the soil level, which in turn facilitates the establishment of other mangrove species and eventually a diverse mangrove forest.

• After an Ice Age

The end of an ice age leaves behind the bare rock as the ice retreats. Mosses and lichens are the first to colonize, followed by grasses and small shrubs. Eventually, trees may grow, leading to a fully developed forest. This is an example of primary succession that has occurred on a very long time scale.

• Moss and Liverworts on Bare Soil

In areas where the soil is exposed, such as after a landslide or in a new garden, moss and liverworts can be the first colonizers. These plants can endure the harsh conditions of bare soil and help to prevent erosion. Their growth and decomposition contribute to the development of richer soil, which allows more plant species to colonize the area over time.

• Hydrothermal Vent Communities

In the deep sea, hydrothermal vents can suddenly become inactive, leading to the death of the unique communities that live there. When a new vent forms, it is colonized by bacteria that can survive in the extreme conditions. These bacteria form the basis of a food web that includes a diverse array of organisms, including tube worms, shrimp, and crabs.

• After a Volcanic Eruption

In the aftermath of a volcanic eruption, the surrounding landscape can be covered with ash and lava, leaving a barren, moon-like surface. Over time, this area undergoes primary succession, with the first organisms to colonize often being lichens and mosses that can grow on bare rock. Gradually, small plants, shrubs, and eventually trees begin to grow, leading to the establishment of a new ecosystem.

• In a Desert Oasis

An oasis is formed when water from an underground river or aquifer comes to the surface of a desert. The water allows plants to grow, and the plants, in turn, provide fo