Environmental biology is one of the critical Biology Topics that involves understanding how humans impact the environment and how to address environmental issues.
What is Ecological Succession – Types of Succession with Suitable Diagrams
Ecological succession is the natural development of a series of biotic communities at the same site, one after the other till a climax community develops which does not evolve further because it is in perfect harmony with the environment of the area. A biotic community is influenced by biotic factors, physico-chemical factors, and geographical factors.
1. Pioneer Community:
The first biotic community which develops in a bare area, is called the pioneer community. It has very little diversity. The stage takes the longest time to change the environment for invasion of the next community.
2. Climax Community:
A climax community is a stable, self-perpetuating, and final biotic community that develops at the end of biotic succession and is in perfect harmony with the physical environment. It is also called the climatic climax community. The climax community has maximum diversity and niche specialization.
3. Seral Community:
The various biotic communities that develop during biotic succession or the intermediate communities between the pioneer and climax communities, are termed as seral or transitional communities. The entire sequence of development stages of biotic succession from pioneer to a climax community is known as sere.
General Processes of Succession
A number of steps are involved in biotic succession
The formation of bare areas without any form of life is called nudation. The cause of nudation may be climatic (e.g., wind, erosion, flood, drought, storm, frost), topographic (e.g., landslide, volcanic eruptions), or biotic (e.g., epidemic, human activities, fire).
Successful establishment of a species in this bare area is called invasion, it is completed in three steps: Migration, Ecesis or establishment, and Aggregation.
- Migration: The transfer of seeds, spores, or other propagules of the first settler species to the bare area is called migration.
- Ecesis: The species that invaded to the bare area must grow, establish, and reproduce for successful succession. Those species that are adjusted to this situation ultimately get established. The entire process beginning with the germination to the formation of reproductive units, is called ecesis.
- Aggregation: After ecesis, the individuals of the species increase in number by reproduction and they get close to each other. This process is called aggregation.
3. Competition and Coaction:
Competition develops for the limited supply of the resources available in the habitat. The competition is mainly for space and nutrition. Competition may be intra-specific or inter-specific. Those organisms that survive such competition will have an increase in their number, the other populations will have a reduced proportion. They might even be eliminated. The development of interactions among members or a biotic community is called Coaction. This might affect the individuals of species in various ways.
The living organisms reciprocally influence and get influenced by the environment. This is known as a reaction. As a result of the reaction, changes take place in the soil, water, light conditions, temperature, etc., of the area. Thus, the environment of the area gets modified, becoming unsuitable for the existing community which in the course of time becomes unsuitable for the existing community which in the course of time is replaced by another community (serai community).
Finally, the terminal community becomes stabilized in the prevailing conditions.
After that, the development of vegetation in an area over time, reached a steady state, which is known as the climax. A climax community can be determined by the general climate of the region, topography, and local microclimate.
Theories Interpreting Climax
Two major theories to define, identify, and interpret the climax communities are monoclimax and polyclimax theory. Monoclimax theory was developed largely by Frederic elements. This theory recognizes only one climax, determined solely by climate, no matter how great the variety of environmental conditions is at the start. This is also known as the climatic climax theory.
The polyclimax theory was developed by Tarsley. The theory considers that the climax vegetation of a region consists of not just one type, but a mosaic of vegetational climaxes controlled by soil moisture, soil nutrients, topography animal activity, etc. R. H. Whittaker proposed a variation of the polyclimax idea, the climax pattern theory. This emphasizes that a natural community is adapted to the whole pattern of environmental factors in which it exists.
Types of Ecological Succession
Ecological succession has the following types.
1. Primary Succession
Primary succession is a biotic succession that occurs on previously bare land, e.g., newly exposed rock areas, sand dunes, igneous rocks, deltas, newly created ponds, or reservoirs. The establishment of a new biotic community is generally slow. The first group of organisms established there are known as the pioneers or primary colonizers. It takes a longer period, e.g., the development of forest climax on a sand dune or barren land may take about 1000 years.
2. Secondary Succession
Secondary succession is a biotic succession that occurs in an area from which a community has been removed and where nutrients and conditions for existence are present, eg., cut-over forest, abundant cropland, plowed fields, and land that have been flooded. Secondary succession is much faster than primary succession because the soil and certain organisms are already present. Surviving seeds, underground stems, persisting and new invading species rapidly grow on the return of favourable conditions. This re-establishes the biotic community through necessary serai changes in due course of time. A destroyed grassland may take 50-100 years and a damaged forest over 200 years to recover fully.
Differences between Primary Succession and Secondary Succession:
|Primary Succession||Secondary Succession|
|1. Succession occurs on a previously bare land.||1. Succession occurs in an area from which the community has been removed.|
|2. Lichens are the first ones to appear.||2. Grasses, shrubs, and weeds are the first organisms to appear.|
|3. It takes about 1000 years to reach the climax community.||3. It takes a shorter time i.e., 200 years to reach the climax community, because some soil is already present, and succession is faster. Fig Abamoloned farmland burned out on cut forests.|
3. Autogenic Succession
It is a succession driven by the biotic components of an ecosystem. It is caused by changes in soil structure and composition. Plant structure can also change the community structure.
4. Allogenic Succession
It is a succession driven by the abiotic components of an ecosystem. It is caused by changes in environmental conditions influencing the population.
5. Autotrophic Succession
It is marked by the presence of floral species and their dominance through the early serai stages of succession. The food web depended on photosynthetic organisms. Autotrophic organisms such as green plants are dominant. It begins in a predominantly inorganic environment and energy flow is maintained.
6. Heterotropic Succession
It depends on preformed organic matter for the food web-based. In it, heterotrophs dominate such as bacteria, fungi, and other consumers. Likewise, this succession starts in an organic environment followed by a progressive decline of the energy contents of the ecosystem.
7. Induced Succession
Human activities can have a powerful effect on ecosystems and the way they change. This is known as human-induced succession, which can lead to changes that are often unexpected and sometimes seriously detrimental to the benefits that people derive from ecosystems.
8. Retrogessive Succession
It is a succession where the community becomes simplistic and contains fewer species and less biomass over time. Some retrogressive lines are allogenic in nature.
9. Cyclic Succession
It is a pattern of vegetation change in which a small number of species tend to replace each other over time in the absence of large-scale disturbance. Observations of cyclic replacement have provided evidence against traditional Clementsian views of an end-state climax community with stable species compositions. Cyclic succession is one of several kinds of ecological succession, a concept in community ecology.
Based on the nature of habitat biotic succession is mainly of two types hydrarch and xerarch.
Hydrosere or Hydrarch: A Series of biotic communities that develop in a newly formed pond or lake, is called hydrosere. The various stages together with their chief components of plant and animal species during primary succession in water are
1. Phytoplankton Stage:
This stage constitutes the pioneer community. Some blue-green algae, green algae, diatoms, and bacteria, etc., are the first organisms to colonize the primitive medium of the pond. Soon a balance is created by the appearance of zooplankton which feed on phytoplankton. Death and decomposition of plankton produce organic matter. The latter mixes up with clay and silt at the bottom to form soft mud favourable for the growth of the next serai stage.
2. Submerged Stage:
The bottom lined by soft mud having organic matter is favourable for the growth of submerged plants like Hydrilla, Potamogeton, and Najas. They are rooted in the mud and form dense growth. The older plants and buried parts of other plants form humus on their death and decay. This enriches the newly built-up bottom and makes it favourable for the growth of the next stage.
3. Floating Stage:
The roots of the plants of this stage are anchored in the floor and their leaves float on the surface of water, e.g., Nymphaea, Nelumbo, and Trapa. Some free-floating plants also arrive, e.g., Lemna, Azolla, Salvinia, Eichhornia, etc. All such plants reproduce rapidly through rhizomes and spread in the entire pond. Animal life rapidly spreads during this stage. Hydra, frogs, water snails, numerous kinds of insects, and tortoises live. The amount of water decreases very quickly. Soil is quickly built up. In a short time, water becomes very shallow.
4. Reed-swamp Stage:
Typha, Cyperus, and other such plants constitute reed swamp vegetation. Their growth is dense. These are amphibious in habit. A part of their body remains under water and a part remains exposed to the outside. Their roots are spread like mats over the soil. After sometimes sedge-meadow stage appears.
5. Sedge-meadow Stage:
Because of the successive decrease in water level and further changes in the substratum, species of Cyperus, Juncus, Carex, Eleocharis, etc., colonize this area. Except in monsoon, the soil remains dry at all times and a grassland made up of various grasses develops.
6. Woodland Stage:
Due to the disappearance of the marshy sedge-meadow stage, the soil becomes drier for most time of the year. This area is now invaded by terrestrial plants, which are some shrubs and trees. By this time there is much accumulation of humus with rich flora of microorganisms. Thus, the mineralization of soil favors the outcome of new trees in the area.
7. Climax Forest Stage:
The forest stage is the climax community. The woodland community is gradually invaded by several trees. In tropical climates with heavy rainfall, there are forests of Acer, Quercus, etc. But in regions of moderate rainfall, there develops deciduous forests. Thus in hydrosere, the phytoplankton stage is the pioneer community, the forest is the climax stage or community, whereas the intermediate stages are the serai communities.
Xerosere or Xerarch
This type of succession occurs on a bare rock or some other dry habitat. The main factors in such a habitat are lack of water and dry soil, intense light, fluctuations of temperatures from very high to very low and winds turn out to be significant factors. Xerosere is further of different types
- Lithosere – Starting on a barren rock
- Psamnosere – Starting on sand
- Halosere – Starting on salt marshes
1. Crustose Lichen Stage:
A bare rock cannot hold water, there is no soil. The substratum is very hard. In such an area the pioneers are crustose lichen. During rain or heavy dew, the lichen propagules settle over the rock surface. They get attached to the rock at several points by means of their rhizoids. They can tolerate temperature and wa¬ter extremes. Some such crustose lichens are Graphis, Rhizocarpon, and Lecanora. Lichen secrete lichen acids and carbonic acid. Both acids cause etching of the rock surface creating small pores. The pores become gathering points for organic matter, dust particles, and water.
2. Foliose Lichen Stage:
Fertile crevices built up by crustose lichens invite foliose lichens (e.g., Parmelia, Dermato carpon, etc.). This lichens are fixed to the substratum at a single point. They secrete more lichen acids. The process of breaking up rock becomes more rapid. At an interval of time, bryophytes make their appearance.
3. Moss Stage:
The bryophytes particularly the mosses develop and spread very rapidly. They spread like mattresses over the rock. They grow and spread very rapidly during monsoon and remain dormant in a dried condition. The first group of mosses (e.g., Tortula, Grimmia, Polytrichum, etc.) are hardy mosses and can withstand desiccation for long periods. Moisture-loving mosses then invade the area, e.g., Biyum, Hypnum, Fissidens, etc.
4. Herbs Stage:
This stage is constituted by shallow-rooted grassed as Poa, Festuca, Solidago, etc. Due to the more extensive growth of leafy mosses, there are more soil and minerals due to leaching out from the overlying vegetation. This changed habitat favours the arrival of biennials and perennials.
5. Shrub Stage:
Seeds and rhizomes of xerophytic shrubs, invade the area occupied by perennial grasses, e.g., Ziziphus, Capparis, Rhus, Rubus. Shrubs are larger and their roots reach greater depth causing further cracks in the rocky substratum and hence helping in more soil formation. The shrubs shade the area, make it more moist, and invite hardy trees and several types of animals.
6. Climax Community:
Several hardy and light-demanding trees grow in the area occupied by shrubs, Slowly environment becomes more moist and shadier so that plants of the climax community spread in the area. The type of climax community depends upon the climate. It is a rainforest in a moist tropical area, a coniferous forest, or a deciduous forest in a temperate area. Grassland appears in areas with less rainfall. The shrubs and tree stages are then omitted. Development of climax forests on bare rocks or sand dunes, i.e., primary succession, takes at least 1000 years.
Difference between Succession on land and Succession in Water:
|Succession on Land||Succession in Water|
|1. The succession starts with lichen and blue-green algae.||1. The succession starts with phytoplankton.|
|2. The process is seen throughout the area.||2. The process is seen where the water level is low.|
|3. The first process occurs slowly.||3. The first process occurs very fast.|
Differences between Pioneer Community and Climax Community:
|Pioneer Community||Climax Community|
|1. The first biotic community develops in a bare area.||1. Final biotic community that develops at the end of biotic succession.|
|2. The area is initially bare.||2. A transitional community covers the area.|
|3. Individuals are small-sized.||3. Individuals are small as well as large sized.|
|4. Pioneer community builds up the soil.||4. The soil is already built up.|
|5. Individuals have a high growth rate.||5. Individuals have a slow growth rate.|
Comparison between Hydrarch and Xerarch Succession:
|Hydrarch Succession||Xerarch Succession|
|1. Phytoplanktous are the pioneer species.||1. Lichens are the pioneer species.|
|2. Climax community is found to develop on the edge only.||2. Climax community develops in the entire area.|
|3. Succession in the initial stage is fast.||3. Succession in the initial stage is rather slow.|
|4. The aquatic environment is converted into a mesic (well-hydrated) environment.||4. A xeric (Poorly hydrated) environment is converted into a mesic environment.|
|5. Gradual filling up of water bodies leads to forested land.||5. Gradual conversion of bare land into a forested area.|
Both these succession leads to a mesic environment. Comparison of pioneer and climax community species with respect to Hydrarch and Xerarch Succession:
|Hydrarch Succession||Xerarch Succession|
|Climax Communities||Develops on Edge||Formed in Whole Area|
The products of ecosystem processes that have environmental, aesthetic, and indirect economic value are termed Ecological services.
Soil formation and soil protection are the major ecosystem services accounting to nearly 50% of their total worth. Plant cover protects the soil from drastic changes in temperature. There is little wind or water erosion as soil particles are not exposed to them. The soil remains spongy and fertile. There are no landslides and no floods.
2. Release of Oxygen:
The plant cover of natural ecosystems absorbs polluting gases, causes the setting of suspended particulate matter, removes CO2, and releases O2. A purified air becomes available.
There is an increase in atmospheric humidity, good rainfall, and a moderating effect on climate.
4. Nutrient Cycling:
There is no depletion of nutrients but the same are repeatedly circulated and recirculated. It keeps the soil fertility intact.
Bees, other insects, and birds visit nearby farmlands and areas around the forests for pollination of crop plants, bushes, and trees.
Natural ecosystems are a source of bio-diversity with a variety of genes, gene pools, species, and habitats. Biodiversity also has aesthetic value which at¬tract holiday tourism.
A large number of cattle are allowed to graze in the wild so that pressure on crop plants is reduced.
Ecosystems provide habitats to wildlife.
9. Wet Land:
It protects the terrestrial land from the effects of flood. This wetland also released the precipitation of pollutants for the elimination of pollution from the water.
10. Other Values:
Natural ecosystems are a source of spiritual, cultural, and aesthetic values.
Robert Constanza and his colleagues have put the value of ecosystem services to 33 trillion dollars. It is nearly twice the global gross national product (GNP) of 18 trillion dollars. 50% of it is for soil protection, prevention of floods, and mitigating droughts. The value is 10% each for nutrient cycling and recreation. It is 6% each for climate regulation and habitat for wildlife.