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Xerarch Succession
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Keywords: Xerarch, Xerarch Succession, Plant Succession, Types of Xerarch Succession, Xerosere, Ecological Succession, Lichens.
What is Xerarch Succession?
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Xerarch Succession is a type of plant succession that starts on bare land in dry environment. Over some time, these barren lands are colonized by plants and then into forests. Dunes and rock deserts are examples of such types of communities.
Types of Xerarch Succession
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During the early stages of xerosere succession, environmental communities appear in extremely dry areas like unweathered rock surfaces, sand deserts, rock deserts, and dune deserts.
- Lichens and mosses are xerarch species that colonize these arid lands and then gradually promote complex plant communities.
- Xerarch Succession is of two types: Lithosere Succession and Psammosere Succession.
Lithosere Succession
Lithosere succession is a type of succession that begins on a bare rock surface.
- Bare rock surfaces are colonized by the pioneer species, i.e., the lichens and the mosses.
- They are responsible for breaking the rocks and making soil with time.
- After the soil builds up over time, plants, including herbs, shrubs, and trees, grow and expand the plant community, forming a mature ecosystem.
Psammosere Succession
This type of succession begins on sand deserts and sandy areas are colonized by the pioneer species, i.e. grasses and mosses.
- These species are responsible for soil development, which becomes stable with time.
- After the accumulation of soil, plants, and trees expand the dune ecosystem, providing an ecosystem for both plants and animals.
Stages of Xerarch Succession
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There are six stages of Xerarch Succession:
Crustose Lichen Stage
The first stage of xerarch succession is the crustose lichen stage, in which crustose lichens like Rhizocorpon and Lecanora colonize the bare rocks.
- These lichens produce carbonic acid that disintegrates the rocks, setting up for the next phase.
- Wind and water help travel these lichens via soredia and spores.
Foliose Lichen Stage:
The second stage of succession is the foliose lichen stage, in which foliose lichens store water and collect dust particles that help in producing substrate.
- Parmelia and Dermatocarpen are examples of foliose lichens responsible for producing a layer of soil.
- These lichens also raise the acidity of the soil and humus deposition, casting shade on crustose lichens and limiting their growth.
Moss Stage:
In this stage, humus and soil acidity give rise to xerophytic mosses like Tortula, Grimmia, and Polytrichum.
- As mosses are rich in organic and inorganic compounds, they fertilize the soil as soon as they die.
- They then produce a thick layer that helps improve soil water retention, thereby giving rise to herbaceous plants.
Herbaceous Stage
The Herbaceous Stage is the fourth stage, also known as the Plant Stage.
- Humus and minerals are deposited due to an increase in moss growth, leading to increased water retention capacity.
- The growth of xerophytic herbs like Aristida and Poa takes place. Initially, perennials and biennials follow annual herbaceous plants.
- Mosses are displaced and the growth of shrubs takes place in the next stage.
Shrub Stage
In this stage, shrubs like Phytocarpus overshadow the herbaceous plants because of their thick structures. The roots of the shrubs penetrate the soil and cause large cracks in the rocks that help in the development of soil.
- Climax Stage
The Climax Stage is the final stage of xerarch succession, also called the forest stage, and is dominated by the vegetation of woody plants.
- Humus from the bushes creates favorable conditions for the growth of trees.
- The climax stage is a stable stage that gives rise to plants like Woodfordia, Eugenia, Sterculia, and Terminalia.
Sample Questions
Ques. What is an ecological succession? Give examples. (2 marks)
Ans. A series of changes in the species with the change in environment is called an ecological succession. Coral leaf ecological succession and Acadia National Park are examples of the same.
Ques. Define Hydrosere. (2 marks)
Ans. Hydrosere is also known as hydrarch succession. It is a type of succession that starts from water and then eventually forms a forest. Hydrosere generally begins in water bodies like shallow ponds and lakes.
Ques. Mention the stages of xerarch succession and which stage has an ecosystem dominated by woody plants. (2 marks)
Ans. There are six stages of xerarch succession:
- Crustose Lichen Stage.
- Foliage Lichen Stage.
- Moss Stage.
- Herb Stage.
- Shrub Stage.
- Climax Stage.
The last stage which is the climax stage has an ecosystem dominated by woody plants.
Ques. What is primary and secondary succession? (2 marks)
Ans. Primary and Secondary Succession are types of ecological succession.
- Primary succession begins in areas where there is no soil.
- Secondary succession begins after the destruction of primary succession. For example, when the climax community is destroyed by fire it gives rise to primary succession.
Ques. What are the characteristics of pioneer species? (2 marks)
Ans. Following are some of the traits of pioneer species:
- Pioneer species are resistant to drought.
- These species have a shorter life span.
- They require light for seed germination.
Ques. How is the soil produced in xerarch succession? (1 mark)
Ans. Soil is produced by the pioneer species, lichens. After colonizing the barren land, these species break the rocks by releasing an acid that helps in weathering and soil formation.
Ques. Is halosere also a type of ecological succession? (2 marks)
Ans. Yes, halosere is also an example of ecological succession.
- This type of succession takes place in saline environments for example salt marsh.
- The pioneer species of halosere have thick and fleshy leaves. For example, Chenopodium.
Ques. What happens after the degeneration of rocks by lichens? (2 marks)
Ans. After the degeneration of rocks by lichens, a layer of soil gets deposited on the surface, and the lichens die. This indicates the end of the lichen stage and the beginning of the moss stage.
Ques. What is the role of mosses in xerarch succession? (2 marks)
Ans. Mosses compete with lichens for nutrients and water by moving in the soil. The mosses disintegrate and form a thick layer over the soil surface to improve soil and water retention.
Ques. Is cyclic succession a type of plant succession? (2 marks)
Ans. Yes, cyclic succession is a type of plant succession.
- In cyclic succession, the change in the ecosystem occurs cyclically.
- Some plants remain inactive most of the time but emerge at once leading to variation in the structure of the ecosystem.
Ques. Mention any two advantages of ecological succession. (2 marks)
Ans. Ecological succession has several advantages but two of them include:
- The diversity of species is increased because of variations in species structure.
- Variations in nutrients result in the colonization of new plant communities.
Ques. What is a sere? Mention its types. (2 marks)
Ans. A change in the series of communities in a given area is called a sere. Sere can be of different types: Hydrosere, Xerosere, Lithosere, Psammosere, Senile, and Halosere.
Ques. What factors can lead to an ecological succession? (2 marks)
Ans. Climatic, biotic, and topographical factors can cause an ecological succession.
These factors include
- Wind,
- Fire,
- Soil erosion, and
- Natural disasters like earthquakes, landslides, etc.
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