Ecological Succession is central to the study of ecology. In this article, we will answer the question ‘What is ecological succession? its definition and types”.
A careful study of a portion of land left to fallow reveals the amazing reality of ecological succession. In a few years, the once bare land becomes occupied by a variety of plant species. And if given more time, grows from grassland into a bush and then the growth of shrubs and forest trees.
This process not only involves the development of plant species in an environment but, the development of microbial and other animal species as well.
Definition and Explanation of Ecological Succession
Ecological succession is the gradual but steady process of the formation of an ecological community. It is the process by which the structure of a biological community evolves. A process of change in the species structure of a community over time.
According to Dennis Baldocch of the University of California, Berkeley, succession is the orderly process of community development that is directional and predictable. It results from the modification of the physical environment by the community Succession is community-controlled even though the physical environment determines the pattern, rate of change, and limits.
Ecological succession is caused by disturbances of different intensities, sizes, and frequencies that alter the landscape. A disturbance is any relatively discrete event, in time and space, that modifies the structure of populations, communities, and ecosystems and causes changes in resource availability and the physical environment.
A disturbance can be naturally induced or humanly induced. Examples of natural disturbances are mortality, (age, density, self-thinning), treefall, wildfires, volcanoes, flooding, hurricane/tornadoes, insects/disease, windthrow, tsunami, logging, landslides glaciers sea-level rise or retreat. Human-Induced disturbances are: logging, plowing, mining, dam removal
Ecological succession was first observed in the 19th century as scientists such as French naturalist Buffon observed that poplars precede oaks and beeches in the natural evolution of a forest. While studying forest development in Blekinge, Ragnar Hult in 1885 discovered that grassland becomes heath before the heath develops into the forest. He was the first to use the term ‘succession’.
From his study, birch dominated the early stages of forest development, then pine (on dry soil) and spruce (on wet soil). If the birch is replaced by oak it eventually develops to beechwood. Swamps proceed from moss to sedges to moor vegetation followed by birch and finally spruce. https://en.m.wikipedia.org/wiki/Ecological_succession.
During his study at the University of Chicago, Henry Chandler Cowles found out that vegetation on dunes of different ages might be interpreted as different stages of a general trend of vegetation development on dunes
Types of Ecological Succession
- Primary succession
- Secondary succession
- Autogenic succession
- Cyclic succession
- Allogenic succession
- Autotrophic succession
- Heterotrophic succession
- Induced succession
- Retrogressive succession
- Directional succession
The two major types of ecological succession are primary succession and secondary succession. Others include Autogenic succession, Cyclic succession, Allogenic succession, Autotrophic succession, Heterotrophic succession, Induced succession, Retrogressive succession, and Directional succession.
1. Primary Ecological Succession
Primary ecological succession takes place in lifeless places. These are regions where the soil cannot sustain life. They are usually new and unoccupied. Events such as landslides, rock flow, larva flow, formation of dunes, fire, severe windthrow, or logging lead to the formation of these new habitats.
Primary succession, therefore, follows the formation of new land surfaces consisting of rock, lava, volcanic ash, sand, clay, or some other exclusively mineral substrate. Since soil is a mixture of mineral material, decaying organic material, and living organisms, we can simply agree that there is no soil present before primary succession takes place.
2. Secondary Succession
On the other hand, secondary succession occurs in areas where a once existing community has been lost. It is characterized by small-scale disturbances that do not eliminate all life forms and nutrients. These disturbances may remove or damage the vegetation, but do not remove, destroy, or cover the soil.
The process of secondary succession is faster than that of primary succession. Pioneer plants of secondary succession start from roots or seeds remaining in the soil or from seeds carried in by wind or animals from surrounding communities.
Primary and secondary succession follow similar trends. Aside from plants, microorganisms and animals also undergo ecological succession. Microbial succession can occur in new habitats such as leaf surfaces, rock surfaces recently exposed by glaciers, and animal infant guts.
Secondary succession occurs in microbial communities when microorganisms grow on recently dead trees or animal droppings.
3. Autogenic succession
Autogenic succession is a type of succession whereby replacement by new communities is caused by its vegetation or the vegetation of the existing community. Simply put, it is the replacement of the existing community by a new one by the factors of the same environment.
4. Cyclic Succession
Cyclic Succession is a type of ecological succession that there is a repeated occurrence of certain stages of succession.
5. Allogenic succession
Allogenic succession is one whereby unlike in autogenic, succession s caused by any other external condition and not by existing vegetation itself.
6. Autotropoic succession
Autotrophic succession is one in which there is an early and continued dominance of a community by an autotrophic organism called green plants.
7. Heterotropic succession
In Heterotropic succession, heterotrophs such as bacteria, actinomycetes, fungi, and animals occupy a community during the early stage of dominance.
8. Induced succession
Induced succession is a type of ecological succession that is caused by disturbances such as overgrazing, pollution, and scarping.
9. Retrogressive succession
Retrogressive succession is a type of ecological succession in which there is a return to a simpler and less dense community. Retrogression happens instead of progression as a result of the destructive effects of organisms.
10. Seasonal Succession
Seasonal Succession is the formation of a new community in different seasons of the year.
Stages of Ecological Succession
- Stabilization or climax
The earliest creations in succession are often small, have simple structures, and may reproduce in large numbers. But as succession continues, the small organisms are replaced by larger ones. These larger creatures feed on the smaller ones.
Every community begins with a few plants and animals known as pioneers. They grow from pioneers to stable and self-reproducing climax communities. In between the early stage of colonization and the formation of climax, the community is the seral community. A seral community is found in an ecosystem advancing towards stability. Communities usually experience more than one seral community before climax conditions are attained.
A seral community consists of simple food webs and food chains and exhibits a very low degree of diversity. The entire sequence or series of communities is called a Sere. A sere can also be defined as a sequence of vegetation types occurring during succession.
Seral succession in aquatic habitat is known as a Hydrosere. When it occurs on bare rock surfaces and sandy areas, it is called a Lithosere or Psammosere. A sere starting in saline soil or water is called a Halosere. Xeroxes is a sere that starts in a dry, waterless environment.
Ecological succession undergoes five stages in general: nudation, invasion, competition, reaction, and stabilization or climax stages.
This is the first stage of ecological succession. Development begins in a barren area, where no form of life has ever existed. This development can be caused by climatic factors (glacier, volcanic eruption, flooding, hails), biotic factors (epidemic, human activities), or topographic factors (soil erosion, landslide).
At this stage, a species through migration, enosis, or aggregation becomes established in a formally bare area. In migration, seeds, spores, or other propagules of the species are introduced into the bare area by agents of dispersion (air, water, or living organisms).
Enosis is the successful establishment of migrated plant species into the new area. It involves the germination of seeds or propagules, growth of seedlings, and starting of reproduction by adult plants. Aggregation is the successful increase in the population of an immigrant species through reproduction. The aggregation phase is the final stage of invasion.
This stage is characterized by the development of intraspecific as well as interspecific members of the community. This happens under certain conditions such as limited food supply and space.
At this stage, living organisms influence the modification of the environment. These modifications eventually make the area uncomfortable for the existing community. Therefore, they will be replaced by another community that adapts to these changes.
5. Stabilization or climax
This is the stage at which the community becomes occupied with the climax community. The climax community may also be changed by aging, storm, diseases, and by other biotic and abiotic factors. Climate is usually the chief cause of stabilization in ecological succession.
When a climax community has become established, the species that make up that community tend to remain in possession of the area because they do not leave that environment. Those species also favor the growth of different dominant species. It is generally believed that a community does not ever change after it has attained climax. This is not fully true because factors such as aging, storm, diseases, and other biotic and abiotic factors can cause changes in a climax community.
Stages of Succession in Lakes and Ponds
Ecological succession in lakes and ponds undergoes 7 Stages. These include the Plankton, Submerged, Floating, Reef swamp, Sedge Meadow, Woodland, and forest stages. It begins with the germination of spores that reach in water through wind or animals.
When these phytoplankton dies off and decay, a large amount of organic matter and nutrients are added and some rooted submerged hydrophytes (Elodia, Hydrilla, Elodea, ) begin to appear on the new substratum.
When the depth of water reaches about 4 to 8 feet, the submerged vegetation starts disappearing and then the floating plants make their appearance gradually in that area. Constant interactions between the plant and aquatic environment cause physical and chemical changes in the habitat.
The substratum rises vertically and t floating plants such as Nelumbmm, Trapa, Pistia, Nymphaea, Wolffia, Lemna, Aponogeton, and Limnanthemum replace the submerged vegetation.
After this stage comes the reef swamp stage where the floating plants start disappearing gradually and their places are occupied by amphibious plants ( such as Bothrioclova, Typha, Phragmites, Scripus, ) which can live successfully in aquatic as well as the aerial environment.
With time, vegetation grows from shrubs to medium-sized trees and then to the development of climax vegetation. In these forests, all types of plants are present. Bacteria, fungi, and other microorganisms are found here.
Stages of Succession in Bare Rocky Areas
The first stage of ecological succession in bare rocky areas is the crustose kitchen stage where crustose and lichen are the pioneer species. The lichens secrete carbonic acid in excess. They migrate through their spores and soredia and their migration is facilitated by wind and water.
This is followed by the Foliose Lichen Stage where their leaf-like thalli cover the rock. When the supply of light is cut off the crustose lichens begin to die. Foliose lichens absorb and accumulate water and minerals and check the evaporation of surface water. They also secrete carbonic acid which further pulverizes or loosens the rocks into small particles.
The next stage is the moss stage where the existing foliose lichens start disappearing and are replaced by xerophytic mosses. These mosses develop rhizoids that penetrate deep into the rocky soil. When they die off, their decaying older parts form a thick mat over the rock surface, which increases the water-holding capacity of the soil. This favors the growth of herbs.
The roots of these plants penetrate down almost to the level of unpulverized rock. Decaying leaves stems, roots, and other parts of the plants the form of humus and increase the water holding capacity of the soil. With this, Xerophytic shrubs (such as Rhus, Phytocarpus, Zizyphus, Capparis) gradually occupy the area. From dwarf and widely spaced. Then mesophytic trees grow densely and become dominant.
There are initial, continuing, and stabilizing causes of ecological succession. Initial causes include climatic and biological causes such as fire, the wind blows, etc. Continuing causes are are migration, aggregation, competition, etc. While climate is the main stabilizing cause of ecological succession.
Examples of Ecological Succession
- The succession “garden” plot
- Acadia National Park,
- The volcanic island of Surtsey
- Formation of Coral Reefs
1. The succession “garden” plot
In April 2000, The Succession “Garden” Plot. was established. Pioneer plant species were species that could tolerate periodic mowing that controlled the grass ecosystem. When the mowing stopped, other plant species began to develop.
Over time, the soil was able to retain more moisture and its undisturbed soil-litter interface allowed greater diversity of plants to grow and thrive. Later on, taller, woody plants became established which over-shadowed the sun-loving weed community
2. Acadia National Park,
In 1947, Acadia National Park, in Maine, suffered a large wildfire that destroyed over 10,000 acres. Thus, about 20% of the park was destroyed. Reclamation seemed impossible, therefore, the area was left to natural reclamation.
Over the years, secondary succession has successfully taken place in the park. Species diversity has grown to an extent that deciduous forests have grown on the park to replace the evergreen trees that used to exist in the park.
3. The volcanic island of Surtsey
Another example of ecological succession is that of The volcanic island of Surtsey, located off the coast of Iceland. The island was formed in 1963 as a result of a volcanic eruption that took place. It naturally underwent succession. The succession started with the arrival of seeds through ocean currents, to the appearance of fungi and mold.
Two to five new species arrive on the island yearly. Currently, there are 30 plant species, 89 bird species, and 335 invertebrate species living on the island.
4. Formation of Coral Reefs
Coral reefs form over time through ecological succession. The primary ecological succession in a coral reef is the colonizing of rocks by small coral polyps. These polyps will grow and divide many times to create coral colonies. The shapes and shelter of the coral colonies eventually attract small fish and crustaceans that live around the coral.
Smaller fish are food for larger fish, and eventually, a fully functioning coral reef exists. The principles of ecological succession, while developed in the context of plants, exist in all established ecosystems.
Importance of ecological succession
- Ecological succession is of many benefits to nature. It enables the production and harvesting of food crops consumed by humans.
- It is important for the growth and development of the ecosystem
- It is responsible for the growth of new species in bare areas.
- It initiates the colonization of new species in an ecosystem.
- Ecological succession leads to the maturity of a community.
- It leads to a greater diversity of a community.
- It helps balance the energy flow of a community.
- The study of succession helps us understand other ecological phenomena.
- It helps in predicting changes in biodiversity and ecosystem services.
FAQs on Ecological Succession
What is the ultimate role of ecological succession in an environment?
The ultimate role of ecological succession is the attainment of equilibrium in the ecosystem.
How can you tell what type of succession is occurring?
Observable changes in plant or animal species present in a place are a piece of evidence that ecological succession is occurring.
What is a climax community and is it the end of succession?
Ecological succession was formerly seen as having a stable end-stage called the climax, sometimes referred to as the ‘potential vegetation’ of a site, and shaped primarily by the local climate. This idea has been largely abandoned by modern ecologists in favor of nonequilibrium ideas of ecosystems dynamics.
Most natural ecosystems experience disturbance at a rate that makes a “climax” community unattainable. Climate change often occurs at a rate and frequency sufficient to prevent arrival at a climax state.
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